ESTC 2019 – Tesla’s Colorado Springs Experiment

ESTC 2019, the Energy, Science, and Technology Conference[1], included a presentation and working demonstration by Eric Dollard on Tesla’s Colorado Springs experiment[2] (TCS), which is available through A & P Electronic Media[3]. Due to unforseen circumstances relating to the demonstration co-worker, the generator for this experiment was unavailable after the demonstration for additional experimentation, investigation, and follow-up demonstrations.

In agreement with Eric I suggested that the spark gap generator from the Vril Science Multiwave Oscillator Product[4], (MWO), could be adapted, tuned, and applied to the Colorado Springs experiment, and in order to facilitate ongoing investigation and experimentation throughout the conference period. What follows in this post is the story of how this successful endeavour unfolded in the form of videos, pictures, measurements, and of course the final results.

The first video below shows highlights from the endeavour, video footage was recorded and supplied by Paul Fraser, and reproduced here with permission from A & P Electronic Media.

The second video below shows highlights from the impedance measurements part of the endeavour, video footage again by Paul Fraser, and by Raui Searle.

Figures 1 below show a range of pictures of the original transmitter and receiver setup from Eric Dollard’s TCS demonstration, including the generator used to power the experiment, and key results from the original demonstration. The red “transmitter” coil (RTC) was subsequently modified after the demonstration, (secondary coil re-wound, and with a single copper strap primary), in order to work well with the MWO spark gap generator. The green “receiver” coil (GRC) was left un-modified for the purpose of the endeavour, although it could be fine tuned using the extra coil telescopic extension. Ultimately for on-going experiments using the MWO generator, the GRC would be re-wound and adapted to more closely match the RTC.

The original TCS demonstration was powered by a 1000W linear amplifier generator being driven at ~ 800W output to light a 500W incandescent bulb at the receiver primary, and where the electric power is transferred between the RTC and GRC by a single wire. The TCS demonstration with both coils fully configured and connected to the generator was tuned to a drive frequency of 848.4 kc/s, as can be seen in fig. 1.9 as the selected frequency of the transceiver.

The transceiver is an ICOM-7300 which must have been modified to allow transmit on all frequencies, a modification that allows a radio amateur transceiver to generate a transmit signal outside of the designated amateur bands. This kind of modification turns a transceiver into a powerful bench top signal generator, with full modulation capabilities, and matched output powers from the transceiver alone of up to 100W in the MF and HF bands (300kc/s – 30Mc/s). 848 kc/s is in the MW (MF) radio broadcast band, and amplitude modulation is well suited here for the transmission of voice and music signals, as was also demonstrated in the original experiment.

The ICOM transceiver is connected via a matching unit to the Denton linear amplifier. This specific brand and model of linear amplifier has no matching unit at its input, which is why external matching is required from the ICOM 50Ω output to the lower impedance Denton input. The passive matching unit is shown in fig. 1.10, and also in the schematic of fig. 2.1.

The Denton Clipperton-L is a linear amplifier using 4 x 572B vacuum tubes with a band selected matching unit at its output, and a total output peak voltage of ~ 500V. The lowest band provided internally for matching at the output of the amplifier is the HF 160m band at ~ 1.8Mc/s. The much lower MW signal at 848kc/s would need additional matching and balancing between the amplifier output and the input to the primary of the RTC, (the output of the amplifier is an unbalanced feed e.g. coaxial, whereas the connecting transmission line and the primary are better fed with a balanced feed). The amplifier passive matching unit is shown in figures 1.6 – 1.8, and is also shown in the schematic of fig. 2.1.

The various different experiments conducted in the original demonstration included the following:

Fig 1.13. Shows Eric Dollard finding the null electric field region between the RTC and GRC, and using a 6′ domestic fluorescent tube light.

Fig 1.14. Shows Eric Dollard testing the field surrounding the RTC extra coil extension top load, using a helium-neon gas filled tube.

Fig 1.15. Shows single wire transmission of electric power, and fully lighting a 500W incandescent light bulb at the primary of the GRC.

Figures 2 below show the schematics for both the linear amplifier generator and coil arrangement for Eric Dollard’s original TCS demonstration, and a second schematic for the TCS experiment retune using the MWO spark gap generator. The high-resolution versions can be viewed by clicking on the following links TCS Demonstration, and TCS Retune.

Figures 3 below show the small signal impedance measurements for Z11 for the TCS coils, and also the tuning measurements for the coils and spark gap generator together, which were taken throughout the endeavour and used to ensure a well tuned match between the generator and the TCS experiment.

To view the large images in a new window whilst reading the explanations click on the figure numbers below, and for a more detailed explanation of the mathematical symbols used in the analysis of the results click here. For further detail in the analysis and consideration of Z11 typical for a Tesla coil based system click here.

Fig 3.1. Shows the impedance measurements for the RTC with the secondary grounded, the extra coil disconnected, and where the primary tank capacitance has been arranged to be series CP = 40pf, which puts the primary resonant frequency FP at a much higher frequency and far away from the secondary. This would be the proper drive condition for the original linear amplifier generator (LAG) where FP is not arranged to be equal to FS. For the spark gap generator (SGG) it is necessary to match FP as closely as possible to the combined resonant frequency of the secondary and the extra coil together.  The fundamental parallel resonant frequency of the secondary Fs at M1 = 1326kc/s, and as is to be expected with this form of air-cored coil, the FØ180 or series resonant point at which a 180° phase change occurs, is at a higher frequency at 1571kc/s at M2. At M3 = 2398kc/s a tiny resonance is being coupled from the disconnected extra coil which, being mounted in the centre on axis with the secondary, is close enough to have a non-zero coupling coefficient, and hence show some slight resonation reflected into the measurement.

Fig 3.2. Here the extra coil has been reconnected and two resonant features can be noted, the lower from the secondary, and the upper from the extra coil. The effect of the coupled resonance between the two coils with a non-zero coupling coefficient is to push the secondary resonance down in frequency to where the FS at M1 is now at 826kc/s which is very close to the original drive frequency of the linear amplifier generator at 848kc/s. The fundamental resonant frequency of the extra coil, (now in λ/4 mode with one end at a lower impedance connected to the secondary, and the other connected to the high impedance of the extendable aerial), at M3 is now 1725kc/s

Fig 3.3. Here both the RTC and GRC have been connected together to complete the overall system, and where the bottom end of both secondaries are connected together by a single wire transmission line. Both the RTC and GRC have their extra coil adjustable extensions fully extended. It can be seen that both the secondary and extra coil resonant frequencies have been split in two, to reveal four resonant frequencies from the four main coils, 2 in the RTC, and 2 in the GRC. The markers at M1 at 833kc/s and M3 are due to the secondary resonance in the RTC and GRC respectively, and the markers at M5 at 1752kc/s and M7 at 1801kc/s are due to the extra coils. It can be noted that the impedance of the RTC and GRC are not well-balanced the resonance is stronger on the RTC side where |Z| at M1 ~ 741Ω, and M3 ~ 342Ω. During running operation with either the LAG or SGG this would result in more energy stored in the RTC coil, the standing wave null on the single wire transmission line would be pushed away from the RTC and towards the GRC, and less power would be available at the output of the primary in the GRC.

Fig 3.4. Here the lengths of the extra coil extensions have been adjusted to balance |Z| at M1 and M3 at ~500Ω. The RTC extended length was 57cm, and the GRC extended length was 84cm, measured from the copper to aerial join, and to the base of the ball top load. With very fine adjustment, which is very difficult to accomplish, it may be possible to also balance |Z| for the extra coils at M5 and M7. This would result in the ideal balanced and equilibrium state, where the electric and magnetic fields of induction are balanced across the entire system, energy storage is equal, the null point is equidistant between the RTC and the GRC, and maximum power can be transferred between the two coils. In practice, when |Z| for the fundamental secondary resonance is equal, as shown, the overall system can be considered to be well-balanced, and will perform close to its maximum performance. Very slight adjustments to the drive frequency from the generator can then be used to nudge the system into the best overall balance and match. FS at M1 is now 858kc/s which is now close to the original drive frequency of the LAG at 848kc/s.

Fig 3.5. Shows the impedance characteristics of the RTC from the perspective of the SGG. The vector network analyser (VNA) is connected to the outputs of the spark gaps in the generator, so the characteristics include the tank capacitance of 6.1nF and the primary coil, which in this case is 2 turns of 1/4″ copper pipe. It can be seen that the resonant frequency of the primary FP is somewhat below FS as M1 at 549kc/s, and is moving away from M2 and M3. FS has also reduced to 801kc/s at M2 which also shows that the loading in the primary is too much. The inductance of the primary coil, or the tank capacitance, needs to be reduced in order to establish a better match between the generator and the RTC.

Fig 3.6. Here the number of turns of the primary has been reduced to one, which reduces the inductance in the primary resonant circuit with the generator. M1 is now closer to M2 and M3 and the FS has now increased to 819kc/s. The tuning between the generator and the RTC has now swung slightly the other way and the primary is pushing upwards on the secondary characteristics. This state is however a better state of tune than that shown in figure 3.5. It can also be seen that FE for the extra coil is cleaner and less impacted by the primary resonance. Additional fine tuning of the system would ultimately be accomplished by moving one side of the primary connection a certain distance around the circumference of the primary loop, (to form a fractional number of turns in the primary e.g. 1.4), and gain balanced and equidistant spacing for markers M1 and Mfrom M2.

Fig 3.7. Here the single turn copper pipe primary has been replaced with a single turn copper strap, which was deemed to present a lower impedance to the generator, and improve the magnitude of the oscillating currents in the primary. In order to further improve the tuning two 22nF 3kV capacitors in parallel (44nF) were added to one of the outputs of the SGG as shown in the schematic of figure 2.2. This reduced the tank capacitance slightly from 6.1nF to 5.4nF. The inductance of the strap was measured to be 2.5uH which combined with the tank capacitance of 5.4nF provides a theoretical lumped element resonant frequency of 1370kc/s. referring back to figure 3.1 it can be seen that FS, the resonant frequency of the secondary, without the extra coil at M1 is 1326kc/s. So the primary circuit tuned and driven at this point has a very close match to the secondary coil, which ensures that maximum energy can be coupled from the primary to the secondary, and then combined with the extra coil, maximum power can be transferred from the generator to the RTC, and ultimately to the GRC when further connected. For the purposes of this endeavour this state of retune was considered adequate for further demonstration and exploration of the Colorado Springs experiment.

The experimental phenomena observed during the operation of the TCS experiment, retuned to work with the MWO generator, can be seen in the first video on this page.

Summary of the endeavour:

The overall endeavour facilitated the demonstration and exploration of tuning and operating the MWO spark gap generator to work with the Colorado Springs demonstration. In the process the RTC primary and secondary needed to be modified for optimum running with the SGG. Throughout the endeavour a wide range of measurements were demonstrated including:

1. Z11 impedance measurements for the series fed secondary and extra coil, for the RTC.

2. Z11 impedance measurements for the primary combined with the secondary, and the exta coil, for the RTC.

3. Combined Z11 impedance measurements for both the RTC and GRC, where the bottom ends of both secondaries were connected together to form a single wire transmission line.

4. Fine tuning of the system by adjusting the wire length of the extra coil extensions, in order to balance |Z11| in the fundamental and second harmonics.

5. Z11 impedance measurements using a computer connected vector network analyser.

The endeavour also facilitated the demonstration and exploration of the following interesting Tesla related phenomena:

6. Single wire electric power transmission.

7. Longitudinal transmission of electric power.

8. Emission of radiant energy pulses from an incandescent bulb.

9. Radiant energy pulses attracting metal to the bulb.

10. Amplification of radiant energy by interaction with a human hand.

11. Transference of electric power between a TMT “transmitter” and “receiver”.


1. ESTC 2019, Energy, Science, and Technology Conference, A & P Electronic Media , 2019, ESTC

2. Dollard E., Preview of Theory, Calculation & Operation of Colorado Springs Tesla Transformer, 2019, EricPDollard

3. A & P Electronic Media, 2019, EMediaPress

4. Vril Science, Lahkovsky Multiwave Oscillator, 2019, Vril

 

Spark Gap Generator Measurements – Part2

Part 1 of the spark gap generator covered the major components of the system, along with the design steps taken to build a diathermy replica unit (DR). In this part measurements are carried out both in the frequency and time domains, to further understand the operating characteristics, and how best to match the output of the generator to the experimental load. In this part there is also consideration as to how the generator transforms the incoming mains supply to an output suitable for experiments in the displacement and transference of electric power.

The primary purpose of any generator within such an experimental system, arranged to investigate the inner properties and workings of electricity, is to provide the necessary tension to the experiment, in order to change the balance of the electric and magnetic fields of induction within the local region of the experimental system. It is considered that changing the local balance of these fields in turn couples to deeper properties within the energetic dynamics and wheel-work of nature, which according to the purpose or the load of the system generates a response into the local experimental system. In so doing the form of the electrical input to the generator is transformed to another more  suitable electrical output under tension. In other words the energetic balance of the system is based on an inter-dependence between the local source, (in this case the generator), and the “need” or purpose generated in the system, (in this case the load). The inter-action between source and load defines the local electrical characteristics of the system under experimentation.

In the case of the spark gap generator tension is established by considerably raising the potential (voltage) of the output, whilst simultaneously transforming incoming alternating currents (ac), to oscillating currents (oc) in both the primary and secondary coils in the DR. In addition, and most importantly for displacement, there is a brief moment before the initiation of the discharge of the spark where the impedance of the space in the gap is low, but no transient discharge has yet started. At this point it is conjectured that displacement occurs, and an impulse current is drawn into the system for a very brief moment before the spark discharge is established.

After this moment of displacement, current starts to flow from the tank circuit through the spark gaps, dissipating the stored energy in the circuit through the normal process of transference, and in so doing generating oscillating currents in the resonant circuits of the primary and secondary. It is conjectured that exploration of these transient impulse currents may indicate a mechanism for additional energy to be injected into the system, and is part of the larger displacement principle being investigated as an inner working of electricity, and originating from the undifferentiated coherent action of the electric and magnetic fields of induction to re-balance the dynamics of the local system.

Figures 2 below show the small signal impedance measurements for Z11 up to 10Mc/s at the output of the spark gaps, (with the HV unit disconnected), and then with progressive change of tank capacitance to show the change in tuning, and the optimum match between the primary and secondary of the diathermy replica (DR) unit:

To view the large images in a new window whilst reading the explanations click on the figure numbers below, and for a more detailed explanation of the mathematical symbols used in the analysis of the results click here. For further detail in the analysis and consideration of Z11 typical for a Tesla coil based system click here.

Fig 2.1. Shows the resonant frequencies of the both the primary and the secondary coils in the DR. M1 (marker 1) is the fundamental resonant frequency FP of the primary, showing the 180° phase change that takes place at the resonant frequency, and the minimum impedance point of a series resonance where |Z| has no reactive components and only reflects the electrical resistance of the primary coil. FP at 950kc/s is a result of the series combination of the primary coil inductance and resistance LP and RP, and the combined two series banks of tank capacitors CP, and any stray L and C that result from the inter-connecting wires and boundaries to the surrounding medium. RP ~ 0.22Ω is low and indicates a good primary coil size and material, which will enable larger discharge currents to flow, facilitating stronger oscillations to be coupled to the secondary, and an improved power transfer between the primary and secondary coils.

M2 shows the fundamental resonant frequency of the secondary FS = 3180kc/s, and M3 the frequency at which a 180° phase change takes place FØ180 = 3820kc/s. As is normal for a secondary coil where there is considerable distributed resistance across the coil end points FS and FØ180 do not occur at the same frequency, and the parallel resonance formed between LS and the distributed capacitance CS set the fundamental resonance of the coil at M2. When electrical energy is coupled to the secondary from the primary the coil will resonate at the frequency indicated at M2.

Where required FS can be made to more closely match FØ180 by adding additional loading capacitance to the open end (top-load) of the secondary coil. This is a very common practice for large discharge Tesla coils, (designed for powerful streamers), where metal toroids are added as a top-load and add additional loading capacitance bringing FS much closer to FØ180. This also reduces the Q of the Tesla coil and hence is not desirable for experimental coils designed to explore the inner workings of electricity.

It should be noted that the fundamental resonant frequencies of the primary FP and secondary FS do not correspond at the same frequency, as would normally be expected and tuned for a spark gap driven Tesla coil arrangement. Normally to gain maximum power transfer between the two coils their resonant frequencies will be arranged to be the same through tuning of the primary, (Lp or Cp dependent on the type of coil, how it is constructed, and with what materials). This means that in the DR case less power than optimum is coupled to the secondary, and hence the strength of any discharges from the output of the EHT terminal are reduced. Since the DR is based on the original HGF specifications it is conjectured that this may have been desirable for medical diathermy applications to restrict the strength of the EHT discharges by deliberately mis-matching the resonance of the two coils.

The second harmonic of the secondary FS2 occurs at M4 and M5. If the primary is tuned closer to M4 then the secondary coil will resonate at FS2 = 8390kc/s which represents the second odd harmonic of the secondary wire length, 3λ/4. The parallel resonance at M4 is noted to be quite strong, with a similar Q to the fundamental, indicating that the secondary could have a better response to impulse currents generated in the system. Impulse currents due to there very sharp, high energy, wide frequency band, excite a wide range of resonances within a typical Tesla coil system. The ability for the system to respond to such impulse currents largely depends on the overall Q of the coil’s harmonics. The series resistance at M5 becomes the limiting factor in how much power can be coupled to harmonics of the coil, and has risen considerably from M3 from 2.3Ω to 10.8Ω.

It can be noted from part 1 that the designed Fλ/4 (FØ180) was simulated for the coil dimensions, turns, and construction as 3806kc/s which is only ~ 0.4% error from that measured in the small signal Z11 analysis at 3820kc/s, (Fλ/4 occurs at M3, and is based on the λ/4 length of the coil when one end of the coil is at a low impedance, and the other at a high impedance).

Fig 2.2. Shows the dramatic effect of reducing the total tank capacitance CP down to 250pF. The marker number for the primary M1 has been kept the same despite the order of the coil resonances changing across the 10Mc/s band. M1 the series resonant frequency of the primary FP has now moved right up to 5Mc/s, which has also resulted in a reversal of M2 and M3 so the that FS is now above FØ180 at 3150kc/s. The effect of moving the primary resonance point, through the tuned primary tank CP, is to mis-match the primary and secondary resonances the other way, increase the effective series resistance of the primary coil resonance from 0.22Ω to 2.0Ω, but to leave the actual fundamental resonance frequency of the secondary FS with only a ~1% change from 3180kc/s to 3150kc/s. Increasing M1 to between the fundamental FS and the second harmonic FS2 has also had a more dramatic impact on the  frequency of the second harmonic, reducing it from 8390Kc/s to 8200kc/s, a change of ~ 2.3%.

It should be noted that the dependence of FS and FØ180 to tuning in the primary is dramatically different for the flat coil parallel tuned, and the cylindrical case series tuned. For the flat coil, parallel resonance tuned, FØ180 remains more constant with changes in CPP, and is almost exclusively effected only by the secondary wire length, whereas FS, and its harmonics FSN, vary very widely based on changes in CPP. In the cylindrical coil, series resonance tuned, the dependence reverses and FØ180 varies very widely with changed in CPS , whilst FS, and its harmonics FSN, remain more constant with changes in CPS. This emphasises the need for the correct choice in the type of secondary coil used for any specific experiment (e.g. flat, cylinder, equal ratio etc.), and also the correct choice of primary tuning mechanism, (parallel or series). The characteristics and differences, and hence the choice for specific types of experiments, for each of these different coil configurations will be considered and reported in more detail in subsequent posts on the cylindrical coil.

Fig 2.3. Here CP is now increased to 500pF and M1 starts to move downwards again towards the secondary FS. In this case FP is approaching the point of optimum match where the primary and secondary are equally split between the centre point. With CP = 500pF the match is still a little high where the primary is resonating at a frequency above the secondary.

Fig 2.4. Here CP is now increased to 750pF and M1 and M2 are now equidistant either side of FS at M3. Once again FS has not really changed significantly and is still at 3150kc/s. This point of match is in principle the most optimum match between the primary and secondary coils, where maximum power can be transferred between the two coils.

In practise and for maximum streamers it is usually preferred to operate this form of cylindrical Tesla coil, where FP is slightly below FS, due to FS falling when a discharge (streamer) occurs. The discharge causes a change in the impedance of the secondary coil reducing its resonant frequency FS, bringing FS during discharge to an optimum match with the primary, allowing maximum power transfer from the tank through to the secondary discharge.

In experiments to explore the displacement and transference of electric power, where it is preferable not to produce discharge streamers (dissipating the energy of the system through transference), the optimum match where FS = FP is the preferred condition. This is where the Q of the system is maximum, and the continuity between the electric and magnetic fields of induction between primary and secondary are optimum, which in turn ensures the maximum dynamic stability, and best departure point from a system in equilibrium.

Fig 2.5. Here CP is now increased to 1000pF, Fis slightly below FS, (observed in the larger gap between M1 and M2, than M2 and M3), which is around the best empirical match for a Tesla coil designed for maximum discharge as discussed in the previous section.

Fig 2.6. Increasing CP to 2000pF starts to move Fmore rapidly away from FS, the match between the primary and the secondary is reducing, and hence the coupled energy is also reducing.

Fig 2.7. At CP = 5000pF FP is now approaching the DR design of Fig 2.1, FP = 1000Kc/s, and FS remains mainly constant at 3140kc/s, only having changed ~ 0.3% as CP changes in the range 250pF – 5000pF.

Fig 2.8. At CP = 5500pF FP is now very similar to the DR design of Fig 2.1, however FS has not yet increased slightly to match the 3180kc/s in Fig 2.1. CP is somewhat different to the expected ~ 7200pF of the two Cornell Dubiller tank capacitor banks which in combination is 6 capacitors of 47nF in series.

Fig 2.9. Here CP has been increased to 6100pF, where FP matches to the large signal primary resonant frequency observed during the time domain experiments shown below in Fig 3.3 at 895kc/s. FS which is now 3190kc/s has finally moved slightly away from the previously stable 3150kc/s, but notably is now closer to the DR design of Fig 2.1, and also the large signal secondary resonant frequency of 3214kc/s shown in Fig 3.6 below.

Overall the small signal Z11 analysis of the spark gap generator reveals a wealth of detail in understanding how this generator is characterised in the frequency domain, and how best to match the primary tank capacitance to obtain different operating points according to the purpose of the experimental system.

Figures 3 below show the large signal time domain waveforms of the spark gap generator as measured from the low output tap, and illustrate the different stages of the spark discharge burst both in the primary and secondary coils of the generator. The spark gap generator was being run at an input power of 300W, (monitored using a Yokogawa WT200), which was kept constant throughout the measurement of both Figures 3 and 4. Output waveforms were measured using a Pintek DP-50 high voltage differential probe, (max. 6.5kV up to 50Mc/s), which was connected to a HP 54542C oscilloscope to observe and record the output waveforms.

To view the large images in a new window whilst reading the explanations click on the figure numbers below:

Fig 3.1. Shows the burst waveform measured at the low output tap of the DR. The vertical amplitude scale is 1kV/div, and the horizontal timebase is 5µs/div.  The oscilloscope was adjusted to acquire the burst in single-shot mode, triggering at a low to high transition of 1.75kV, where the output delay was adjusted to coincide the trigger to the start of the second full horizontal division. The burst waveform is formed of three major sections, where the first is right at the point of triggering and always involves a very sharp impulse type transition, the second a ring-down of specific frequency based on an exponentially decaying oscillation in the primary coil of the DR, and the third, a ring-down of another specific frequency on an exponentially decaying oscillation in the secondary coil of the DR.

The first section occurs right around the moment of initiation of discharge of the spark gap, and includes a very sharp impulse transition, where the amplitude of this impulse can be many times more than the nominal tension of the high voltage supply. This section  requires more detailed capture and measurement with a more sophisticated experimental setup, and will therefore be considered and reported in a subsequent post. Here it is sufficient to understand that there is an impulse like start to the spark discharge, which only lasts for a very brief moment around the initiation of the discharge, and produces very narrow and sharp amplitude spikes at the very beginning of the output burst.

The second section is established right after the spark discharge has started, and the energy stored in the two tank capacitor banks is being discharged in the primary circuit. Before the spark discharge is initiated the tank capacitors are charged by line frequency alternating current supplied by the output of the high voltage supply, where the charging circuit is formed by the high voltage transformer connected through the tank capacitors to the primary coil. When the tension across the output of the transformer has risen above the combined breakdown voltage of the spark gap unit, the spark discharge begins and the impedance across the spark gap suddenly changes from an open-circuit to almost a short-circuit.

The inputs to the primary tank capacitors are now shorted together by the spark and the tank capacitors discharge their stored energy rapidly through the primary coil. The resonant primary circuit formed by the tank capacitors in parallel with the primary coil cause the discharge to oscillate at a frequency defined by LPCP, and this oscillation lasts until the tank capacitors are completely discharged. How rapidly the capacitors discharge at the resonant frequency and the magnitude of the oscillating currents generated in the primary circuit is dependent on the series resistance presented by the primary circuit, which should ideally be as low as possible, and in the case of the DR was measured in Fig 2.1. to be ~ 0.2Ω.

The oscillating currents in the primary during the spark discharge of the tank capacitors, couple through induction to the secondary of the Tesla coil in the DR, or more clearly, a sudden change to the prior equilibrium state of the electric and magnetic fields of induction energy in the system result in energy being accumulated in the secondary coil. In the third section of the burst discharge this accumulated energy in the secondary transforms to oscillating currents at a frequency defined by the secondary resonant circuit LSCS. The secondary oscillating currents decay exponentially in the secondary coil, (assuming no streamer discharge from the secondary), according to the series resistance presented in the secondary circuit. These secondary oscillating currents again couple through imbalance in the electric and magnetic fields of induction back to the primary circuit, where they can be observed in the output waveform as the third section of the ring-down, which dominates the output when the second section oscillations have become sufficiently small.

The complete burst waveform lasts for about 20µs before decaying to less than 1% of its initial amplitude. Bursts are initiated each new cycle of the line frequency, so for UK standard line input at 50Hz to the high voltage supply, a burst is generated every 10ms, (2 per cycle), or at a frequency of 100Hz.

Fig 3.2. Here the horizontal timebase has been reduced to 2µs/div which accordingly magnifies the burst discharge showing more detail in the first, second, and third sections. In the second section and with careful observation it can be seen that the oscillation is not a pure sine wave, it is actually the oscillating currents of the primary circuit with the smaller oscillations of the secondary super-imposed over the top. The super-imposed secondary currents are not easily discernible in the second section because the amplitude of the oscillation in the primary circuit are large.

As these primary oscillations decay away, and after ~ 8µs, a phase change in the output occurs and the secondary oscillations now dominate the output with an envelope that carries the small decaying primary oscillations. In other words the overall burst waveform is a superposition of the oscillating currents in both the primary and the secondary in both sections two and three, where one or the other can be clearly observed based on the energy stored in the respective resonant circuit, and that coupled forward and backward through the inter-action  of the two coils.

Fig 3.3. Here the horizontal timebase has been further reduced to 1µs/div and the waveform buffer delay adjusted so that section two dominated with the primary oscillations fills almost the entire trace. The transition to the third section can be seen in the last two divisions of the trace. With section two the main focus of this trace the monitored average frequency of trace 1 can be seen to be 895kc/s which is FP, the fundamental resonant frequency of the primary circuit. The amplitude of the primary oscillations is almost 4kVpk-pk at the beginning of the section, and has decayed after 8µs to ~ 1kVpk-pk.

Fig 3.4. Shows the discharge burst in magnified amplitude against the original horizontal timebase rate. The amplitude has been magnified by a factor of 10 from 1kV/div to 100V/div which illustrates clearly the transition to the third section where oscillations in the secondary coil, coupled back into the primary coil, are a superposition of the both the primary and secondary oscillations, and hence the envelope of the waveform in the third section appears similar to an amplitude modulated waveform. Note: the indicated frequency on this trace is not accurate as it is calculated by averaging together sections 2 and 3, and cannot be considered to be the fundamental frequency of the secondary coil.

Fig 3.5. Here the discharge burst is magnified both in vertical amplitude and in the horizontal timebase, and illustrates more clearly the decay and envelope of the secondary oscillations.

Fig 3.6. Here the discharge burst is further magnified in the horizontal timebase and delayed into the third section of the discharge burst, which shows the monitored average frequency of trace 1 to be 3214kc/s which is FS, the fundamental resonant frequency of the secondary coil.

The large signal time domain waveforms have also revealed a wealth of detail about the operating characteristics of the spark gap generator, showing the nature and characteristics of the oscillating output waveform, and with well-defined sections that can be corresponded to the frequency domain properties measured in Figures 2.  The results have also shown impulse like characteristics in the first section of the waveform, that certainly require more investigation and more detailed measurement to clarify if they relate to, and contribute to, the conjecture of underlying displacement phenomena within electricity.

Figures 4 below show a comparison on the same vertical and horizontal scale of the low, medium, and high output taps. It can be seen that the amplitude of the output increases with each successive tap, consistent with the geometry of the primary/Oudin arrangement of the coils.

The low tap produces about 4kVpk-pk initial output, the medium tap 8kVpk-pk, and the high Oudin tap ~ 11kVpk-pk but at considerably reduced current. The medium output tap has been determined to be the best tap for driving TMT experiments, and other experimental apparatus suited to the exploration of the displacement and transference of electric power, where there is high output tension combined with stronger oscillating currents.

Summary of the generator results and conclusions so far:

1. The results and measurements for the spark gap generator correspond well between the frequency and time domain, and give a good insight into how this type of generator works, and the type of output that can be generated. The generator presented in parts 1 and 2 were initially used to confirm the experiments and results of Dollard et al.[1,2], before being applied widely to my own research into the inner workings of electricity.

2. This generator has been proven to be reliable and robust and can sustain indefinitely output powers of 1.5kW, and short bursts over 2kW with the appropriate connections and arranged loads.

3. This generator transforms the low frequency alternating currents of the line input, into high frequency oscillating current outputs, combined with considerably increasing the tension of the output.

4. Analysis, of particularly the time domain results, indicates a first section in the discharge burst that may include impulse currents and effects that are conjectured to involve displacement events. This section requires more detailed measurement and analysis, and will be reported in subsequent posts.


1. Dollard, E. & Lindemann, P. & Brown, T., Tesla’s Longitudinal Electricity, Borderland Sciences Video, 1988.

2. Mackay, M. & Dollard, E., Tesla’s Radiant Matter Replication, 2013, Gestalt Reality

 

Spark Gap Generator – Part1

The complete spark gap generator (SGG), including the diathermy replica (DR), and the MMC capacitor bank unit, is shown in Figures 1 below, and mounted on top of, and connected to the high voltage supply:

In the early days of my research, and before we built the spark gap generator, it was unclear to me which parts of the electrical system were most directly responsible for generating unusual electrical phenomena, whether it be the generator or high voltage source, the types and arrangements of the various coils, or a combination of these elements setup and arranged in a specific manner, tuned in a specific way, and operated in a specific method. Far more consideration is normally given to the experimental components (e.g. coils), their construction, dimensions, materials, and the results that they yield, and much less on the generators that produce the high voltages and currents that are used to power the experimental apparatus.

Over time this appears to have led to an “air of mystery” surrounding the generators that are used in these types of experiments, quite besides a good generator is a complex and involved process to design and build, and can take much more time than any other system component to “get right”. Certainly when I started out by watching the experimental work of Dollard et al.[1,2], I was very much left with the impression that many of the unusual results obtained were mostly a product of the special generator and components used, and the experimental coils allowed these effects to be transformed, observed, and experimented with.

I have not been alone in these impressions, as I have received very similar comments from others in the field that have not actually built a working experimental system for themselves, but rather still feel that “air of mystery” that surrounds the generator and specialised components and materials in the systems construction. Only by building or contributing to a working experimental system, (including the generator), is it possible to really dispel this “air of mystery”, as it becomes possible to understand and characterise how the generator is producing the types of voltages and currents specific to its type.

In addition to this, many of the components referred to in important works such as Dollard et al.[1,2,3], may well have been more readily available in the 80s and early 90s, but are now quite scarce, and often command high prices for working items, or “new old stock” components. For example a 1920s H.G.Fischer diathermy machine used as the primary generator in the experiments of [1] are very rare, and when they very occasionally are available, they are expensive. Without understanding what is inside a generator such as this, and how it is working, it is very difficult to know how to build a comparable generator, or whether one will be able to gain the same types of unusual electrical phenomena demonstrated in works such as [1,3].

This was certainly the place I found myself in the early days where I wanted to begin by reproducing and confirming for myself the unusual measurements and results obtained by others, before using this as an established foundation to advance further in exploring my own ideas and insights regarding electricity, and the displacement and transference of electric power. When I started out there were no good examples of a working diathermy machine currently available, (especially in the UK), so I decided to design and build a diathermy replica for myself, and using readily available materials and components. If this generator could be used to explore unusual electrical phenomena then it would certainly for me increase my understanding enormously of how such generators are designed and constructed, whilst also dispelling the “air of mystery”, and providing a generator design that could also easily be used by others in the field. Later I did finally acquire an original 1920s H.G.Fischer diathermy machine  and have been able to make a characterisation and comparison between the replica and the original.

The posts reporting the Spark Gap Generator – Parts 1 and 2 are the result of building a working high power diathermy replica, which is now routinely used in my daily experiments, and has contributed significantly in bringing me to a core understanding, that all parts of the electrical system play a specific role in the generation of unusual electrical phenomena. In the exploration into the displacement and transference of electric power each part of the system apparatus must first be measured and characterised carefully to establish a well tuned and balanced overall system, and where the electric and magnetic fields of induction are balanced and in a state of dynamic equilibrium.

From this point it is possible to experiment directly into the properties of electricity, and come to an understanding that the unusual phenomena observed are a product of the inner workings of electricity itself, where the generator and experimental apparatus are necessary to set up the conditions and boundaries required to explore these inner properties.  The properties of electricity are there to be revealed rather than “generated”, which also assists greatly in dispelling the “air of mystery” that the generator is the source of the unusual phenomena, but rather, the instrument that provides the necessary tension to trigger the imbalance of the electric and magnetic fields of induction, and hence to observe electrical phenomena within the system. The differences here are subtle but hugely important to the overall understanding of electricity and particularly displacement of electric power.

The circuit diagram for the SGG and peripherals is shown in Figure 2 below, or click here to view the high-resolution version.

In the early days in order to replicate the experiments and results of Dollard et al.[1] , it was considered that the diathermy replica (DR) should be as close as possible to the original, which of course posed a challenge when there was no original from which to take measurements, dimensions, construction methods etc. To overcome this a range of references from the internet were studied, along with available circuit diagrams. The most useful references proved to be a combination of material from [3,4,5], and allowed key dimensions and some circuit component values to be extracted from the images and videos.

Click on the following links to view circuit diagrams for various original H.G. Fischer (HGF) diathermy machines, the Model G2, the Model H, the Model CDC, and the Model A[4].

In any Tesla or resonant coil design it is first necessary to define the desired properties of the secondary coil. With this defined the primary and other components of the system can be designed around the secondary properties. In the case of the DR, and in the absence of any good measurement data, e.g. the resonant frequency of the HGF secondary, the DR secondary was designed according to the known and available dimensions of the HGF secondary, the wire size and type, and the number of turns, (mostly gained from [5]). The dimensions and wire were then adjusted for readily available materials and then key parameters extracted using the software Tccad 2.0[6]. The DR secondary coil properties were adjusted primarily to match F0 the primary resonant frequency of the secondary coil, while keeping the physical dimensions as close as possible,  whilst using readily available material types and sizes. The original HGF and the designed and adjusted DR properties are shown in the following table:

Original H.G. Fischer Model G Diathermy:

From reference pictures and video[5]:

Turns: 90

Wire: Solid copper 20 AWG cotton-clad, total diameter 1.0mm

Secondary Former (OD): 25/8“, 65.7mm

 

Secondary Coil length: 92mm

Primary Former (OD): 31/2“, 89.6mm

Primary Coil: 6 turns 3/16” copper tube

Oudin extended coil: 11 turns 12 AWG solid (2mm) magnet wire

From Tccad 2.0:

L = 340uH

C = 2.87pF

F0 = 5066 kc/s

Fλ/4 = 3978 kc/s

Additional top load Cλ/4 = 1.78pF

Wire length (WL) = 18.9m

Diathermy Replica:

Adjusted for available materials to match F0:

Turns: 98

Wire: 19/32 20 AWG Kynar (PTFE coated), total diameter 1.2mm

Secondary Former (OD): 63mm (standard UK polypropylene pipe)

Secondary Former OD + PTFETAPE + PTFEWIRE = 63.40mm

Secondary Coil length: 120mm (the PTFE wire  coating adds additional length)

Primary Former (OD): 90mm (standard UK polypropylene pipe)

Primary Coil: 6 turns 3/16″ annealed copper tube

Oudin extended coil: 11 turns 14 AWG solid (1.6mm) magnet wire

From Tccad 2.0:

L = 350uH

C = 2.84pF

F0 = 5065 kc/s

Fλ/4 = 3806 kc/s

Additional top load Cλ/4 = 2.03pF

Wire length (WL) = 19.4m

Figures 3 below show how the Tesla/Oudin unit was constructed, and the types of materials used in a simple open structure that can be easily adjusted and modified according to the experimental requirements. Components are mounted on a mdf wooden base, and conductors insulated from the mdf using PTFE and Nylon 66 mounts, bolts, and nuts.

The formers of the primary and secondary coils were first coated with PTFE tape to improve the thermal barrier between the coil and the polypropylene former material when running at high output powers. In addition a small low voltage fan was located under the primary coil to help keep the primary cool at sustained high power outputs. The Tesla EHT output and the HT output taps are all mounted on PTFE insulators both for electrical isolation, but also for good resistance to melting and burning which can occur when drawing discharges from these terminals. Nylon 66 can also be used here, but has lower thermal resistance to discharges, but has the benefit of being a much cheaper material than PTFE.

It is important to note that the secondary coil is located in the primary at the opposite end to the Oudin extended coil. In an early version of the DR the secondary was incorrectly located at the same end as the Oudin extension, which because of the increased tension in both coils easily causes breakdown between the two coils, and led to burn-out of the first secondary coil. The tank capacitor banks are made from 3 series connected Cornell Dubiler 941C03 series 3kV polypropylene film capacitors each of value 47nF, which combined gives 15.7n 9kV for each bank. These tank capacitors have been proven to be long-lasting, and robust, and have never been changed,  even with input powers in excess of 1.5kW and even up to 2.2kW for short bursts of power.

The tank capacitors are force air-cooled, and mounted on insulated conductors which allow for easy connection and adaption to the circuit under test. The capacitance of the tank was initially higher at around 47n to match more closely the HGF schematic of the Model A, but was reduced to its current value after the real HGF was acquired and measured. At 47n the available output power was quite a bit less than with 15.7n per tank, as the primary resonance is pushed lower and further away from that of the secondary, hence reducing the primary currents, and hence the power coupled from the primary to the secondary.

Figures 4 below show how the static spark gap (SSG) unit was constructed.

The SSG unit was at the time the most difficult unit to build when only a large pillar drill, large vice, and bench sander were available in the workshop for mechanical construction. Each electrode of the spark gap is made from 1/4” diameter 99.9% pure tungsten rod 1″ long, (not to be confused with tungsten carbide rods), which were pressed using the vice, into the centre of a drilled A2 stainless steel fine pitch bolt. The bolt had a 6.2mm hole centre drilled, by mounting the bolt in the drill chuck and clamping the drill stationary on the stage, and opposite to how a drill press is normally used. This arrangement made a very rudimentary “lathe” and made it easier to drill a centralised 1.5″ hole down the centre of the bolt. The tungsten electrode was then pressed into the bolt leaving 5mm externally for the spark electrode. Alternating stainless steel washers (large and small) were then threaded onto the bolt and finally tightened with a thin stainless steel nut to form the cooling fins of the electrode body.

Each pair of electrodes were then mounted in threaded aluminium blocks, locked in place with a nut on one side, and with a threaded bakelite handle on the other, to allow adjustment of the spark gap space by winding the bolt in or out of the aluminium block. The aluminium blocks were arranged and mounted to form a series connection of all four spark gaps, and also allowing for tapping from any of the 4 stages for experiments using a single gap, all the way up to 4 series gaps, or 4 parallel gaps with shorting shunts. The adjustable electrode was tensioned in the alumium thread by a small compressed nylon rod, ( from an M3 nylon bolt), which was inserted in a vertical hole drilled above the thread, and then tensioned using a screw locked in the correct place by a nut.

The aluminium spark gap blocks are mounted onto PTFE insulators and then mounted to a wooden base where each gap is suspended above force cooling provided by a pair of low voltage plastic fans mounted into the base of the unit. Overall the SSG unit is robustly constructed and can withstand very large powers in constant use. Tuning of the gaps for optimal running can be made carefully during operation via the four insulated adjustment handles, and is demonstrated in the operation video in Part 2.

Figures 5 below show the MMC tank capacitor bank (TCB) which was used to remove one of the tuned primary stages, and hence increase the efficiency and optimisation of the generator driving, for example, the tuned primary of a TMT (Tesla magnifying transformer).

The SGG used with the DR as a generator is most commonly connected with one of the L, M, or H outputs to the primary stage of a tuned TMT, of which the primary stage would typically consist of a coil with a parallel tuning capacitor. In this arrangement the DR, which in itself is already a tuned primary stage, is now connected to another tuned primary stage. Whilst this was useful for preliminary experiments in confirming the key experiments and results of Dollard et al.[1,2] and keeping the generator as close as possible to an original HGF, it has been shown to be more efficient to eliminate the double tuned primary stage by removing the DR and placing the TCB in its place.

The TCB is simply a standalone capacitor unit exactly the same design as used in the input to the DR. Here the TCB is shown with two pcb MMC banks, but the Cornell Dubilier 941C03 series banks could equally as well be mounted in the same way. Figures 1.6 and 1.7 show how the TCB is connected directly to the SSG, and then in turn the output of the TCB is connected directly to the input of, for example, the tuned primary of a TMT, or some other experiment or load. This creates a resonant drive circuit with the TMT coil in series resonance with the TCB capacitors, and is exactly the same arrangement as internally for the DR, and the HGF. Use of the TCB in replacement for the DR has allowed for an easier and more accurate resonant match between the SSG unit and the TMT load, and with greater power transfer between the two units. Impedance measurements are also simplified by removing one resonant circuit from the generator chain. A very wide range of capacitors can be mounted on the TCB, and for higher power experiments up to 2.5kW output power, force cooling is available via the low voltage fan in the base of the unit.

Overall the spark gap generator whether used with the DR unit or the TCB unit at the output, has proven to be a robust and reliable generator for a wide range of experiments. It has enabled the replication of the key experiments as presented by Dollard et al.[1,2,3,4], as well as forming a flexible and powerful tuned static spark generator for my own experiments in the displacement and transference of electric power, as well as telluric transmission experiments.

Click here to continue to part 2 of the spark gap generator where the operating characteristics are measured both in frequency and time, as well as a short video to show its general operation and running.


1. Dollard, E. & Lindemann, P. & Brown, T., Tesla’s Longitudinal Electricity, Borderland Sciences Video, 1988.

2. Dollard, E. & Brown, T., Transverse and Longitudinal Electric Waves, Borderland Sciences Video, 1988.

3. Dollard, E. & Mackay, M., Tesla Radiant Energy Experiment, Bedini-Lindemann Conference, June 29-30, 2013.

4. Mackay, M. & Dollard, E., Tesla’s Radiant Matter Replication, 2013, Gestalt Reality

5. Sergey Z., Fischer Diathermy Narrating and Exploring a 1920’s Tesla Coil, May 2014, Youtube

6. Chapman R., Tccad 2.0 for Windows, 2000.

 

1920s H.G. Fischer Diathermy

Later in the research, (and after the replica diathermy unit had been designed and built), I was lucky enough to come across a real 1920s H.G. Fischer diathermy unit (HGF), which although being sold untested, and in unknown condition, looked suprisingly good from the pictures. It survived the shipping from the USA to the UK all in one piece, and on closer inspection proved to be in good physical and working condition, including the thermo-ammeter, and the original fuse. The only part missing was the 6V power indicator bulb.

The unit is an early model GP, which is actually a model G in a compact portable cabinet, with a robust carry handle, and metal cabinet corner protectors. Being from the USA the ac line voltage input is specified at 110V 60Hz with a maximum power input of 500W. In the UK this line voltage requires a step-down transformer, a suitable auto-adjusting 1kW transformer was found to be adequate for long-term operation. This post presents detailed pictures, measurements, and an analysis of the HGF as a spark gap generator, and a comparison to the replica diathermy already built and reported in the Spark Gap Generator Part 1 and Part 2.

Figures 1 below show the front-panel of the unit, and in detail, the construction and configuration of the various inner components of the HGF:

The actual circuit diagram for the HGF, which was obtained by opening and measuring the unit, is shown in figure 2 below, or click here to view the high-resolution version. Click on the following link to view the original circuit diagram which appears the closest match to this unit model, and comes from the original Model G2.

The line input is connected through a switch, (also with outputs for a foot switch), to the input of a multi-tap choke. The choke is designed to restrict the current, based on the output tap setting, through the primary of the high voltage transformer, and hence control the output voltage of the transformer and the strength of the spark discharge. The model G has 5 power settings which control the input power measured in the range 75 – 440W @ 120V, (line output of the auto-adjust step-down transformer). The choke is constructed from multiple layers of windings using AWG 18 solid magnet wire, wound over thin cardboard layer separators, and coated in a Shellac type resin to hold all the windings together. The core of the choke is made from many thin mild steel laminations and mounted each end to the front panel by wooden spacer blocks.

The output of the tap selector from the choke is connected to the primary of the high voltage transformer. The primary is mounted on thicker mild steel laminated core that is rectangular in shape, with the primary at one end, and the two secondary coils at the other. The primary is wound again like the choke with multiple layers of, cardboard separated, AWG 16 solid magnet wire, held in place with the same resin, and then externally coated with paper tape. The two secondary coils are again made from many cardboard separated layers, with ~25 windings per layer of AWG 22 solid magnet wire, and structurally held together by thin wooden layers compressed by insulating fibre threaded rod, and plastic threaded round nuts.

The combination of the primary and secondary coils on the laminated steel core forms an early transformer arrangement. The efficiency of this type of basic transformer is not as high as would be expected for a typical modern design, constructed with modern materials. Increased losses in the laminated core and materials lead to more power dissipation and heating during running, although the size and bulk of the construction results in a robust transformer, that can be run all day long at maximum power without overheating. This is further evidenced that the transformer is still functioning correctly, and is not far short of 100 years old!

The two high voltage transformers are connected in series, and with the outer ends of the two coils connected to the outer ends of the 3 series connected spark gaps, via coiled cotton-clad stranded wire. The spark gaps appear to be a tungsten tipped centre electrode, clad with a machined copper heat sink fin. The other end of the centre electrode is very fine threaded, and with a bakelite adjustment handle at one end to fine adjust the gap spacing of each electrode pair. The outer ends of the 3 series connected spark gaps are connected both to the output of the secondary coils, and the inputs to the series capacitors, in the first stage of a typical Tesla[1] “hairpin” arrangement. Further detail regarding the Tesla “hairpin” circuit and its history is given in a summary presented by Kraakman[2].

The two series tank capacitors, ~15nF each, are constructed from alternating thin copper conducting sheets with thin insulating mica sheets. These are sandwiched together between two cotton webbed sheets, insulating them from the outer wooden blocks that compress the capacitor sheets together. The wooden end blocks are compressed together by insulating fibre threaded rod, and plastic threaded round nuts. In fig. 1.6 it is important to note that on the left hand tank capacitor there is another smaller capacitor formed on the outside of the wooden block. This is the floating ground connection capacitor important for diathermy use when connected to a patient. This capacitor prevents the final outputs of the diathermy unit to accumulate to very high potentials relative to ground, which would present a considerable discharge danger to the patient from their body to ground. It is somewhat disconcerting to imagine that the safety of the patient, when connected to this type of high tension generator, was only really ensured by the two series tank capacitors and the floating ground connection capacitor. Failure of any one of these three capacitors would effectively connect the patient to around 6kV @ 100mA at the input line frequency of 50/60Hz!

The two tank capacitors are connected to each end of the primary coil, which is 6 turns of 3/16” copper tube, and then extended by an 11 turn  AWG 12 solid copper wire Oudin coil extension. The low, medium, and high output taps are then derived from the primary and Oudin extension as shown in the schematic diagram of figure 2. The primary and Oudin extension are wound around a 31/2” primary former which appears to be a resin/mica composite material. The primary turns are separated from each other by a cotton woven thread which matches the diameter of the copper tube and wire. Connection between the spark gaps and the tank capacitors, the primary coil, and the output taps, are via 3/16” x 1/16” solid copper flat bar.

The secondary coil is a 90 turn 20 AWG cotton coated magnet wire on a 25/8” cardboard former, and the turns retained in place by the same Shellac type resin. The secondary coil is retained in the centre of the primary former by two wooden end caps, themselves compressed together by another insulating fibre threaded rod, with plastic threaded round nuts. The inner end of the secondary is connected to the common connection as shown in the schematic, and the other outer “hot” end of the secondary is fed through the centre of a bakelite stand-off/insulator through the front-panel and to the high tension Tesla terminal, (ball connector with 4mm socket hole). It is important to note that the secondary coil is orientated within the primary former at the opposite end to the Oudin coil extension, which prevents the very high tensions at the top-end of both the primary and secondary from breaking through the primary former forming a spark discharge path between primary and secondary coils.

The primary output taps are connected through a manually positioned thermo-ammeter shunt that shows rf output current on two ranges 0-1A, and 0-4A. The manual shunt can be positioned to remove the meter from the circuit, or to connect it in high and low range positions. The low range is protected by a 1A slow-blow fuse that shunts a 22Ω 50W wire-wound power resistor. When the fuse blows the shunt across the resistor is removed and the meter is protected by the series power resistor. The overall low-side output of the manual meter/shunt circuit, is connected to the indifferent (ground) terminal on the front-side of the diathermy main panel. The measured component parameters combined with their important physical attributes are shown on the schematic in figure 2.

Figures 3 below show the small signal impedance measurements for Z11 up to 10Mc/s at the output of the spark gaps for both the original HGF and the diathermy replica (DR) unit:

To view the large images in a new window whilst reading the explanations click on the figure numbers below, and for a more detailed explanation of the mathematical symbols used in the analysis of the results click here.

Fig 3.1. Shows the fundamental resonant frequency Fat M1 of the primary circuit, and the fundamental for the Tesla secondary coil FS at M2, and its second harmonic FS2 at M4. FP at 1120kc/s is the series resonant frequency formed by the combination of the two series tank capacitors CP connected together by the spark discharge, in series with the primary coil inductance LP. LPCP forms a series resonant circuit where the reactance of Land CP cancel each other out at resonance, leaving only the series resistance of the primary RP at M1, which in this case is 0.49Ω.

M2 shows the fundamental resonant frequency of the secondary FS = 2900kc/s, and M3 the frequency at which a 180° phase change takes place FØ180 = 3180kc/s. As is normal for a secondary coil where there is considerable distributed resistance across the coil end, points FS and FØ180 do not occur at the same frequency, and the parallel resonance formed between LS and the distributed capacitance CS set the fundamental resonance of the coil at M2. When electrical energy is coupled to the secondary from the primary the coil will resonate at the frequency indicated at M2. It is also to be noted that the Q of the resonance at M2 is considerably lower than expected, showing that losses in the secondary coil, materials, and mountings are considerable, where rf energy is being both dissipated in RS, and leaking out of the circuit formed by LSCS through parasitics to the surrounding medium. The low Q of the secondary considerably impacts the energy stored in the system, and will reduce considerably the rf oscillating currents in the secondary, which can be seen in figures 3.

The second harmonic of the secondary FS2 occurs at M4 and M5. If the primary is tuned closer to M4 then the secondary coil will resonate at FS2 = 8140kc/s which represents the second odd harmonic of the secondary wire length, 3λ/4. The parallel resonance at M4 is noted also to be very low Q, and similar in this case to the fundamental. The low Q of the secondary can most likely be attributed to, firstly, the cardboard former of the secondary coil, which over considerable time will have absorbed moisture, and presents a considerable leakage or parasitic resistance to the windings of the secondary coil. Secondly, the windings in themselves are only cotton-clad un-insulated (bare) magnet wire, which also presents a significant leakage path to a moisture impregnated cardboard former. Thirdly, the cardboard former is mounted to the primary via wooden end boards which themselves can absorb moisture, and when combined with moisture in cardboard former of the secondary could also form a significant leakage between the windings of the primary (bare copper) and the secondary coils.  It is conjectured that the Q of the secondary when the HGF was new, or much younger, would have been better than now measured, but still due to the nature of the materials used, would still present a much lower Q than that which can be obtained by using plastic formers, and with magnet wire either PTFE coated, or high temperature varnish coated.

Fig 3.2. For comparison the same small signal impedance measurement is shown from the spark gap generator diathermy replica (DR). Due to the slightly different geometric sizes, of the readily available materials used, for the primary and secondary, and the modern equivalent of the tank capacitors, the key resonant frequencies of the primary and secondary are at slightly different points. However the general characteristics of the frequency markers remains very similar on the horizontal scale.  The series resistance of the primary circuit at resonance for the DR is less than half that for the HGF, showing that larger primary currents can be generated in the DR providing stronger output currents in the low, medium, and high primary taps.

The big difference between the HGF and DR is in the Q of the secondary coil, which is very much larger, and well-defined, in the case of the DR. This shows the difference largely between the types of materials used to construct the secondary, which in the case of the DR is a plastic polypropylene former, with PTFE coated Kynar secondary windings, insulated from the plastic polypropylene former of the primary, by nylon 66 connecting bolts. All these plastic insulating mediums do not suffer with moisture absorption over time, do not degrade significantly over normal time spans, and present a very high impedance between the primary and secondary coils, which reduces any leakage currents in the secondary to very low values. Hence the Q of the secondary circuit is very sharp and well-defined.

Figures 4 below show the large signal time domain waveforms of the HGF as measured from the indicated output taps, and illustrate the different stages of the spark discharge burst both in the primary and secondary coils of the generator. The HGF was being run at an input power of ~ 300W, (monitored using a Yokogawa WT200), which was kept constant throughout the measurement. Output waveforms were measured using a Pintek DP-50 high voltage differential probe, (max. 6.5kV up to 50Mc/s), which was connected to a HP 54542C oscilloscope to observe and record the output waveforms.

To view the large images in a new window whilst reading the explanations click on the figure numbers below. For a detailed description of the different sections of the spark discharge refer to the analysis of figures 3 and 4 in Part 2 of the Spark Gap Generator post.

Fig 4.1. Shows the burst waveform measured at the low output tap of the HGF. The vertical amplitude scale is 1kV/div, and the horizontal timebase is 5µs/div. This figure shows clearly the  second section, a ring-down of specific frequency based on an exponentially decaying oscillation in the primary coil of the HGF. The third section, a ring-down of another specific frequency on an exponentially decaying oscillation in the secondary coil of the HGF is too small to be observed on this vertical scale. The maximum amplitude of the burst is ~ 5kVpk-pk, and lasts for about 7.5µs before decaying to less than 1% of its initial amplitude.

Fig 4.2. Here the horizontal timebase has been reduced to 500ns/div and the waveform buffer delay adjusted so that section two dominated with the primary oscillations fills the entire trace. The monitored average frequency of trace 1 can be seen to be 1077kc/s which is FP, the fundamental resonant frequency of the primary circuit, which corresponds well to that measured in the small signal impedance measurements at M1, of 1120kc/s.

Fig 4.3. Here the vertical amplitude and horizontal timebase have been reduced from fig. 4.1, in order to show the very small third section of discharge burst, that occurs from the secondary ring-down reflected into the primary circuit. The secondary ring-down is barely 100Vpk-pk and reflects the very low Q of the secondary fundamental resonant frequency FS, as shown in fig. 3.1. Due to the low Q from the high leakage through the materials used, the third section ring-down has a low amplitude and decays away very quickly, only lasting in this case ~ 4µs after the primary ring-down in section 2.

Fig 4.4. Here the third section has been magnified and the monitored average frequency of trace 1 can be seen to be 2929kc/s, which again corresponds well to that measured in the small signal impedance measurements at M2, of 2900kc/s.

Fig 4.5. The low tap burst, again on the original scales, for amplitude comparison with the following two figures.

Fig 4.6. Shows the burst waveform measured at the medium output tap of the HGF, and on the same scale as before. The inital burst amplitude has increased to ~ 8kVpk-pk.

Fig 4.7. Shows the burst waveform measured at the high Oudin output tap of the HGF, and on the same scale as before. The inital burst amplitude has increased to almost 12kVpk-pk.

A comparison of some of the key characteristics of the HGF and the replica diathermy already built and reported in the Spark Gap Generator Part 1 and Part 2, are shown in the following table:

H.G. Fischer Model GP Diathermy:

Primary Coil: 6 turns 3/16″ copper tube

Primary Former (OD): 31/2“, 89.6mm

Oudin extended coil: 11 turns 12 AWG solid (2mm) magnet wire

Seconday Turns: 90 turns, 20 AWG cotton-clad magnet wire

Secondary Former (OD): 25/8“, 65.7mm

From figures 3. Z11:

FP @ M1: 1120kc/s

RS @ M1: 0.49Ω

FS @ M2: 2900kc/s

FS2 @ M4: 8140kc/s

From figures 4 (large signal time domain, LSTD @ 300W):

FP: 1077kc/s

FS: 2929kc/s

VL (pk-pk): 5kV

VM (pk-pk): 8kV

VH (pk-pk): 12kV

Diathermy Replica (SGG Parts 1 and 2):

Primary Coil: 6 turns 3/16″ annealed copper tube

Primary Former (OD): 90mm (standard UK polypropylene pipe)

Oudin extended coil: 11 turns 14 AWG solid (1.6mm) magnet wire

Secondary Coil: 98 turns, 19/32 20 AWG Kynar wire (PTFE coated)

Secondary Former (OD): 63mm (standard UK polypropylene pipe)

From figures 2. Z11 (Spark Gap Generator – Part 2):

FP @ M1: 950kc/s

RS @ M1: 0.22Ω

FS @ M2: 3180kc/s

FS2 @ M4: 8390kc/s

From figures 3 LSTD @ 300W (Spark Gap Generator – Part 2):

FP: 895kc/s

FS: 3214kc/s

VL (pk-pk): 4kV

VM (pk-pk): 8kV

VH (pk-pk): 11kV

In summary, the original H.G. Fischer medical diathermy unit explored in this post is a robust, self-contained, and easy to use generator suitable for some preliminary experiments and replications in the field of Tesla and electricity research, where high tension oscillating currents are required, e.g. with a TMT experiment. The HGF’s lower overall performance, in comparison to the replica diathermy unit, largely results from age related wear and tear, component degrading, and generally lower quality, or less suitable, materials for high voltage applications. Having said this, the HGF is almost 100 years old, and still working more than adequately as a high voltage generator, which is in itself an impressive accomplishment from another time. Without access to an original HGF, it has been shown in other posts, that a good high performance generator with very similar yet improved characteristics, can be constructed using readily available materials at a very affordable cost.

Click here to continue to part 1 of the spark gap generator where the diathermy replica is designed and constructed.


1. Tesla, N., Experiments with alternate currents of very high frequency and their application to methods of artificial illumination,  American Institute of Electrical Engineers, Columbia College, N.Y., May 20, 1891.

2. Kraakman, N., A Brief History of the Tesla Hairpin Circuit, December 7, 2017, Waveguide

 

Multiwave Oscillator Impedance – Part 2

In part 2 of the multiwave oscillator impedance (MWO) measurements we take a look at the high frequency impedance characteristics Z11 for the MWO resonator rings (top-load). The MWO Tesla style drive coil measured in part 1 needs to be separated from the MWO top-load for this type of measurement, because the impedance and load of the drive coil masks out any resonant features at higher frequencies, making it impossible to measure the MWO when connected to the top of the secondary coil and measured at the input to the primary coil.

Experiments, operation, and measurements in Tesla coil based systems, and indeed in my own research regarding the displacement and transference of electric power, are normally limited to experimental apparatus which operates at maximum in the HF band < 30Mc/s of the electromagnetic spectrum. At 30Mc/s the corresponding wavelength λ is 10m. As a standard rule of thumb in high frequency or RF measurements the feature size of the element under measurement should be < λ/10 to be considered as a discrete lumped element in the system, and therefore not subject to impedance transformations through transmission line characteristics or other distributed network characteristics. At the upper end of the HF band this means that active measurement regions < 1m in size or length can be considered to have only small, if any, transformation and change on the impedance outside of that attributed with its discrete lumped element network.

As we progress to higher frequency measurements in the VHF band (30 – 300Mc/s) and even above in the UHF band (300Mc/s – 3Gc/s) very great care needs to be taken regarding the length and size of cabling and connections, the feature sizes of components within the measurement network, the impedance match or mismatch between transmission line sections and discrete components, and any other stray, parasitic, or proximity effects arising from boundary conditions that are both metallic or dielectric in nature. Accordingly, much greater care and attention needs to be taken to calibrate as accurately as possible directly to the plane of measurement, and then to normalise out measurement effects between the calibration plane and measurement apparatus.

In this part we are concerned with measurement up to ~1Gc/s (λ = 30cm), and where the λ/10 length is only 3cm. At λ/4 quarter-wavelength we would expect to see a complete impedance transformation along a transmission line from a very low impedance (short-circuit) at the output of the source generator to a very high impedance (open-circuit) at the end of a wire or measurement plane. Accordingly we need to keep connections small and efficient which represents in itself a unique challenge when connecting to the MWO rings, which at UHF frequencies represent a large distributed network of inter-connected transmission line elements, with complex boundary conditions. Subsequent parts will look at the MWO rings as an antenna with corresponding radiation resistance and defined radiation pattern and particularly in relation to the transmitter – receiver configuration of the complete MWO system.

For this part, and to measure as accurately as possible Z11 for the MWO rings directly, and up to frequencies in the order of ~1Gc/s, it was necessary to make a connecting jig that allowed for extension of the reference plane from the VNA-SDR directly to the mounting spheres of the outer driven ring of the MWO. Figures 1 below show the measurement setup, signal feed adapter, MWO mounting jig, calibration elements, and overall arrangement of the high frequency impedance measurement apparatus.

To view the large images in a new window whilst reading the explanations click on the figure numbers below.

Fig 1.1. Shows the overall measurement setup with the VNA-SDR connected to the MWO mounting jig by a short SMA terminated RG316 cable, and the other end to the signal feed adapter (SFA), and standard calibration elements.

Fig 1.2. The SFA mounts directly to high voltage terminals, that are themselves connected to the brass mounting bolts used to hold the MWO rings to the jig. The jig is constructed predominantly in nylon 66 with a wooden internal support for strength inside the main jig supprt column. The high frequency path length and connection effects are normalised out by extending the calibration reference plane right to the brass bolt mounting points for the MWO outer ring. The SFA in this case is used with shorted series capacitance feed, and is balanced with equal weights of copper on the positive and negative feed paths, which includes the SMA connectors and the RG316 cable to the VNA-SDR. Equal weights of copper, or more accurately at high frequencies (> 3Mc/s), equal volumes of copper assist in balancing the boundary conditions for the electric and magnetic fields of induction and so reducing impedance mis-matches in the signal feed path. As for part 1 an SFA with 3Gc/s balun was also tried but found to be largely unsuccessful in the small signal measurements due to the masking of high frequency detail, which results from the balun coupling transformer dominating the frequency characteristics in the mid to high-band frequencies.

Fig 1.3. The calibration elements fit directly onto the end of the MWO brass mounting bolts. With no element attached the mounts are calibrated for open-circuit, a single-sided pcb element is used for the short-circuit, and a single-sided pcb with 50Ω surface mount resistor in the centre for the calibrated load.

Fig 1.4. Shows the MWO rings mounted to the measurement jig.

Fig 1.5. An improvement to the calibration procedure removed the SMA connecting cable by mounting the VNA-SDR directly to the SFA by SMA coupler. In this configuration some additional resonant features were removed from the normalised calibration results.

Fig 1.6. The final measurement setup for the high frequency MWO impedance measurements with VNA-SDR directly mounted to the SFA, which is in turn directly mounted to the jig, and where the calibration plane is at the point where the MWO outer ring brass balls meet the brass mounting bolts.

Figures 2 below show the Z11 impedance characteristics of the calibrated reference plane and the lower high frequency measurement band 100kc/s – 500Mc/s. The entire high frequency band was split into two in order to best comply with the calibration bands within the VNA-SDR instrument. At 500Mc/s the instrument internally changes reference method and level, and sensitive measurements cross-band are not recommended. Therefore the measurements are calibrated into a lower band 100kc/s-500Mc/s and an upper band 500Mc/s – 1.3Gc/s.

Fig 2.1. Calibration for the 50Ω reference element over the band. Markers M1, M3, and M5 show the consistent calibration across most parts of the band. At M2 at 138Mc/s and M4 at 377Mc/s there are resonances within the calibrated signal path which are too significant to normalise out. These points will need to be factored into the measurement results to remove features of interest, if any, that correspond at these frequencies. At these 2 points features in the results are considered measurement artifacts that arise due to the measurement system and inter-connection between the instrument and the MWO rings at the calibration plane.

Fig 2.2. Shows the rich range of resonant features that result from the MWO rings and their inter-action across the band. In this first result markers M1 – M12 are used to identify the lower 12 set of features, and in the next set of results the upper 12 set of features. There is no corresponding feature at 138Mc/s as seen in the calibration scan, and hence this point does not need to to be removed from the results. The first 250Mc/s of the results show a number of strong resonant points indicated by the large phase changes occurring at M4, M6, M8, and M9, and most likely attributed to resonances in the outer few rings of the MWO. There are also smaller phase inversions across the first half of the results occurring at M1, M2, M5, M7, M10, and M11 which most likely arise due to resonant inter-actions between the outer few rings of the MWO. At M12 287Mc/s  a large peak change in |Z11| occurs for a very small phase inversion, which would likely indicate where the outer drive ring of the MWO becomes self-resonant, in a similar way to that of the primary in the drive coil which becomes self-resonant at ~38MC/s. The point at M12 may also correspond to the 2nd harmonic of this point with the fundamental occurring at M8, this however being less likely due to the very low impedance swing at M8 to ~6.9Ω indicating that M8 is more likely to be associated with the fundamental resonance of one of the few outer rings, but not the driven ring.

Fig 2.3. Shows the markers on the upper 12 set of features. At M10 375Mc/s there is a large resonance, the only in the upper 250Mc/s of the results, which also very closely corresponds to the calibration feature noted in Fig 2.1. at M4 at 377Mc/s. The close correspondence of these two points means that the feature at M10 needs to be attributed to a strong resonance in the calibration path which could not effectively be normalised out by the calibration procedure. Otherwise in the upper part of the reults there are some small phase inversions at M11 and M12 which could be tentatively linked to the fundamental resonant frequencies of some the rings further into the MWO centre. In the upper part of the results we start to see a general masking, smearing, and suppression of further detail, not necessarily because the detail is not there, but rather the coupling between rings is not sufficiently loose to allow for the natural resonance of each ring to be reflected in the results, and combined with rapidly increasing losses, large reductions in Q, and decreasing amplitude of oscillation as the results move towards the centre of the MWO. This could be further tested and measured by decreasing the coupling factor between each of the rings by changing the structure of the MWO from a flat set of rings to a cone configuration, where each of the rings retain the same diameter but are separated further apart vertically on the cone yielding a three-dimensional MWO structure. The other way to measure and assess this further is to remove every other ring in the flat MWO so reducing the coupling between rings and also reducing the large number of inter-active resonances. The process of starting with one ring inside the driven ring and subsequently adding ring by ring taking an impedance scan with each ring, would also assist in clarifying which fundamentals occur from which rings, and which features occur due to cross-coupling between the rings.

Figures 3 below show the Z11 impedance characteristics of the calibrated reference plane and the upper high frequency measurement band 500Mc/s – 1.3Gc/s.

Fig 3.1. The calibration of the upper high frequency band shows very good consistency and results for the 50Ω reference load up to M3 at 1096Mc/s. Above this point the signal attenuation is such that the returned measurement currents to the VNA-SDR are so small as to be falling outside the lower dynamic range of the instrument, and hence the results become progressively more inaccurate and noisy. It is to be noted that the base 50Ω reference load can still be extrapolated visually to the end point ar 1300Mc/s. However, above ~1Gc/s the results on this measurement apparatus and setup are considered to not be of further use as can be more clearly seen in the next result.

Fig 3.2. At the lower end of this band markers M1 – M5 continue the upper band of the previous results in most likely showing fundamental resonances and maybe even some inter-actions between some of the more inner rings of the MWO e.g. rings 4-7. It is unlikely that any details can easily be discerned for the inner rings 8-11 where the signal reflections are very small, and stronger coupling between rings has largely smeared out the detail and suppressed the Q of the response.


Overall the high frequency impedance measurements have presented a wealth of detail particularly in the lower part of the band and with discernible results being contributed to by as many as the first 6-8 rings inside the outer driven ring. It is also clear that cross-coupling between rings will contribute to very high frequency components to be emitted from the MWO, even though such detail is largely outside of the scope and dynamic range of the measurement technique used here. A useful comparison measurement would be to look at the range of frequency components generated during normal high tension operation of the complete MWO system, using a spectrum analyser instrument with capabilities into the Gc/s range. The high frequency impedance characteristics still need to be measured for the complete MWO system where both transmitter and receiver are connected to the system, which will be reported in a subsequent part.