Telluric Transference of Electric Power – MF Band 2-8 Miles

This experimental post is a follow-on from the Telluric experiment presented in Transference of Electric Power – Single Wire vs Telluric. In that previous experiment a Tesla Magnifying Transformer (TMT) apparatus, consisting of TX and RX cylindrical Tesla coils, were connected together via a 18m point-to-point telluric transmission medium, and with ground connection cables 26m in total between TX and RX secondary coils. In the medium-frequency band (MF) at 1.86Mc, in the mid-field region, 500W input power to the TX coil generated ~ 80mW of output power at the RX coil, from a combination of the telluric-wave and radio-wave. In this new experiment the same TMT apparatus and generator is used, and the telluric transmission medium is extended into the close far-field region at 2 and 8 mile field locations from the TX coil. In both locations natural water features were used as the telluric ground connection for the RX coil, and the transmitted signal could be clearly received, and was shown to result from the combination of a telluric-wave component through the ground, and a radio-wave component above ground. It is conjectured that at the 2 mile location the longitudinal magneto-dielectric (LMD) transmission mode was dominant in the telluric cavity between TX and RX, and the transverse electromagnetic (TEM) mode was dominant at the 8 mile location.

The video experiment demonstrates and includes aspects of the following:

1. Portable Tesla receiver (RX) setup and tuning, using a cylindrical coil tuned in the 160m amateur radio band, for radio-wave and telluric-wave field experiments in the close far-field region.

2. Telluric ground connection using a submerged aluminium metal plate, firstly in a natural lake connected to a river 2 miles from the lab transmitter (TX), and secondly in a man-made reservoir 8 miles from the TX.

3. Small signal ac impedance measurements using a vector network analyser to tune the RX Tesla coil to the series and parallel resonant modes.

4. Fine tuning to different modes, and optimal received signal strength at 1.86Mc, using a telescopic aerial at the top-end of the RX secondary coil.

5. Comparison of radio-wave and telluric-wave measurement by re-tuning the RX coil from the Telluric ground plate connection, to an ungrounded single wire bottom-end extension.

6. At both 2 and 8 miles the CW audio tone could be received and heard at only 10W TX input power.

7. At 2 miles, 6 bars of signal strength were measured at 10W TX power at 1.86Mc for the telluric-wave and radio-wave combined, and 1 bar for the radio-wave only.

8. At 8 miles, 4 bars of signal strength were measured at 400W TX power at 1.86Mc for the telluric-wave and radio-wave combined, and 2 bars for the radio-wave only.

9. The lower parallel resonant mode of the RX Tesla coil was found to receive the maximum signal strength at both 2 and 8 miles.

10. The lower parallel resonant mode was found to be much more sensitive to body and object proximity than the series resonant mode.

11. It is conjectured that at the 2 mile location the longitudinal magneto-dielectric (LMD) transmission mode was dominant in the telluric cavity between TX and RX, and the transverse electromagnetic (TEM) mode was dominant at the 8 mile location.

Video Viewing Note: In the video the telluric-wave (in the ground) is referred to as the ground-wave, and the radio-wave (over the ground) is referred to as the sky-wave, and not to be confused with the amateur radio definitions of ground and sky wave.

The experimental apparatus, generator and operation, and the TX ground system, is exactly the same as that used in Transference of Electric Power – Single Wire vs Telluric, and is discussed and presented in detail, along with the full experiment schematic, in that post. Operation of the generator in this field experiments is via a research colleague at the lab, and setup, tuning, and operation of the generator can be viewed in detail in the single-wire experiment video presented in the aforementioned post.

A key measurement in the telluric experiments which needs some consideration is the process of measuring the radio-wave of a radio transmission. For all radio transmission, and as transmitters are almost always grounded down to earth, the major component of the transmission is the propagating TEM wave from the radio transmitter antenna to the receiver antenna. In relation to a telluric experiment, we cannot assume that all the power transferred from the TX to the RX coil is via the telluric channel through the ground, as there will also be a radio-wave component at the receiver. We also cannot simply remove the bottom-end ground connection of the RX coil to measure this radio-wave component, as this will change the wire-length of the secondary cavity, and hence change its fundamental series resonant frequency, and any connected receiver which is tuned to the transmitter frequency will erroneously show no received signal, simply because the RX coil is not correctly tuned to the transmit frequency.

To accomplish the radio-wave part of the experiment, and as demonstrated in the video experiment, the telluric ground connection is removed from the RX coil, and is replaced with a single wire 10m in length which is NOT connected into the ground or to any other grounded end-point. The telescopic aerial at the top-end of the RX coil is now fine adjusted so that the series mode resonant frequency of the RX coil matches the transmit frequency. This is accomplished by maximising the received signal at the receiver at the correct TX frequency, and then cross checked by VNWA measurement to confirm correct tuning of the RX coil. In this way the RX coil is now tuned to the correct frequency for receiving the transmitted signal, but is also not connected into the ground.

The signal strength now received on the radio receiver, or power meter, is a result of the radio-wave contribution only, and is less than the combined radio-wave and telluric-wave, as can be seen in the video experiment. The proportion of radio to telluric wave can also give a good indication as to the dominant transmission mode involved in the transference of electric power between TX and RX coil. Equal radio and telluric components tend towards a dominant TEM mode of propagation between the two, or with a combination of TEM and LMD, with the TEM mode dominant. A much larger telluric wave can indicate a dominant LMD mode, and this is demonstrated at the 2 mile field location.

Small Signal AC Input Impedance Measurements

Figures 2 below show the small signal ac input impedance Z11 measured directly on the RX coil of the TMT system, and using an SDR-Kits VNWA vector network analyser, as used on many experimental pages on this site.

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

Fig 2.1. Shows the small signal ac input impedance Z11 of the RX cylindrical Tesla coil, connected via the aluminium grounding plate submerged in a natural river-fed lake at the 2 mile location. The grounding plate is connected to the bottom-end of the RX secondary coil via an 8m 6AWG micro-stranded, silicone coated cable. The RX coil was tuned by adjusting the length of the secondary top-end telescopic aerial, as shown in the video, and in this measurement shows tuning to the lower parallel mode, (in this case the parallel mode of the secondary coil), at ƒL = 1.86Mc @ M1. The RX coil is setup without using balanced parallel modes, as with very small signal reception experiments the additional capacitive loading appears to reduce the amplitude of the measured signal via the Sony ICF-2001D radio receiver. At ƒL the input impedance, (output impedance presented to the radio receiver), is RL ~ 1719Ω. The higher impedance of the lower parallel mode is more suited than the low impedance of the series mode, to directly feeding the Sony radio AM external antenna input, and hence the input impedance of the super-heterodyne first stage receiver in the Sony. Maximum signal reception results were consistently accomplished in the field using the lower parallel mode tuned to the transmit frequency of 1.86Mc.

The fundamental series resonant mode here occurs at ƒO = 1.99Mc @ M2, and again can also be tuned to 1.86Mc by longer extension of the telescopic-aerial. A comparison of the receiver measurements were made in the video against the lower parallel and series modes, and it was determined that the lower parallel mode produced the best results for measurement with the Sony radio receiver, and the series mode would be better for direct power measurements using the HP435B with HP8481H thermocouple power sensor which has a 50Ω input impedance. For the most accurate direct power measurements the output of the RX coil should ideally be matched to the 50Ω input impedance of the sensor, ensuring maximum power transfer from the RX receiver coil to the HP power measurement system. If and when higher powers can be measured using direct power measurement, then a 2:1 current balun would be suitable to affect quite a good match between the RX coil primary output RS ~ 29.6Ω, and the HP power sensor at 50Ω. The upper parallel mode ƒU = 3.96Mc @ M3 originating from the primary coil, cannot be used in this particular experiment as it cannot be tuned down sufficiently low to 1.86Mc using either additional wire length (lowering the series mode), or loading the RX primary coil directly with parallel capacitance.

Fig 2.2. Here the RX coil at the 2 mile location has been tuned to the lower parallel mode ƒL = 1.86Mc @ M1 with the 10m ungrounded single wire at the bottom-end of the secondary coil, and adjustment of the wire-length of the secondary via the telescopic aerial length from 39cm to 45cm. The Q of the RX coil is noticeably higher from being ungrounded and the lower parallel resonant mode impedance is higher at RL ~ 2666Ω. The series resonant mode ƒS = 1.99Mc @ M2 is slightly stronger, and has a lower impedance RL ~ 17.5Ω. Otherwise the characteristics are very similar to when the aluminium telluric ground is being used. This tuned characteristic using the 10m ungrounded single wire was used to measure the radio-wave component of the received signal, which at the 2 mile location, was much lower than the telluric-wave component.

Fig 2.3. Shows Z11 of the RX coil connected via the aluminium grounding plate submerged in a reservoir at the 8 mile location. The parallel mode is here tuned to 1.85Mc rather than 1.86Mc, and there is a consistent 1Hz tuned error throughout this experiment at the 8 mile location. When checked the 1Hz difference did not make a discernible difference to the received signal strength or reception at the field location when using either the lower parallel or series resonant modes. It is interesting to note that the Q of the RX coil system is higher at the 8 mile location, and is more similar to the 10m single wire result in fig. 2.2, than the telluric-plate result in fig. 2.1. It could be considered that this may indicate that the telluric connection to the earth was not as good at the 8 mile location, something which was certainly reflected in the much reduced received signal strength measurements.

Fig 2.4. Here the series mode is now tuned at 1.85Mc, and it is interesting to note that the series mode impedance is again not much higher than that for the 10m single wire results in fig. 2.2, again suggesting that the telluric connection is not as good at the 8 mile location. So both the lower parallel mode and the series mode are closer here to the 10m single wire results achieved at the 2 mile location, and that may suggest that the 8 mile location was more suited to reception of the radio-wave, and less to the telluric-wave. This was indeed what was measured, that the telluric-wave and radio-wave contributed almost equally to the received signal strength at this location, and a lot of transmitter power was needed to get a well-defined signal strength measurement.

Fig 2.5. Shows the balanced mode of the RX coil, and with the series resonant mode tuned to the transmitter frequency. Note that for clarity the magnitude of the impedance scale, |Z| (blue) has been increased from the previous 500Ω/div to 2000Ω/div. The parallel modes from the primary and secondary coil were balanced using a primary loading capacitance of CPRX = 282pF, and this balanced condition in a TMT has been shown to be beneficial to achieving a very high transfer efficiency in single wire mid-field region experiments in the High-Efficiency Transference of Electric Power series. In this telluric experiment, in the far-field region, this balanced condition was found to introduce too much loading in the RX coil given the very small signals being received, which led to reduced signal strength measurements.

The capacitive loading in the primary coil was removed, and appears sub-optimal for these types of very low power level telluric reception measurements. If and when higher power can be transferred via the telluric transmission medium, the balanced mode may be necessary to maximise the LMD transmission mode, and hence the received telluric-wave. It should be noted that the TX coil is tuned and driven by the generator at its series fundamental resonant mode at 1.86Mc, and with the lower and upper parallel modes balanced using primary capacitive loading CPTX = 403pF, which was found consistently to be the most efficient setup for the TX coil and linear amplifier generator, used in both in this telluric experiment and the experiments presented in Transference of Electric Power – Single Wire vs Telluric.

Fig 2.6. Here it was tested to see the maximum balance that could be accomplished between the upper and lower parallel modes, and whilst keeping the lower parallel mode tuned to the transmitter frequency. This characteristic was tuned using a primary loading capacitance of CPRX = 60pF, a significant reduction in loading capacitance from the full balanced mode in fig. 2.5. This produced better signal strength results than the full balanced mode, but still not as good as the unloaded results with no additional primary tuning capacitor. At these very low reception powers it was concluded that the balanced mode simply attenuates the signal too much, and especially in the case were the telluric-wave is not very strong, and the LMD mode is not dominant.

Telluric Transmission in the High MF Band Far-Field

In the first field location 2 miles from the transmitter it was possible to clearly receive with 6 bars of signal strength at only 10W TX power at 1.86Mc for the telluric-wave and radio-wave combined, and 1 bar for the radio-wave only. The attenuation of the signal at 1.86Mc under the ground appears enormous, and it was considered in the previous experiment Transference of Electric Power – Single Wire vs Telluric that this loss is dominated by absorption of the transmitter power by the earth directly surrounding the main telluric ground system in the high medium-frequency band. In the previous experiment only 18m from this telluric ground system the measured power had already dropped from 10W TX power to 1.25mW at the RX coil.

So transmitted power in the earth surrounding the telluric ground system has already reduced by almost 4 orders of magnitude even before it is only 10s of meters away from the ground system connection. When we consider the result achieved 2 miles away the power would have dropped into the micro-watt level to produce the kind of signal strength received by the Sony radio receiver, and so we can conjecture that the transmission over the 2 miles was actually more efficient, than the transmission from the TX secondary coil through the ground system and over the distance of a few 10s of metres. This may also imply that there is very considerable power losses in the interface between the copper of the ground system and the earth, and even with significant water irrigation of the ground system, and relatively low measured impedance at the transmitter frequency.

It is very interesting in the 2 mile location that there was also a large difference in the received combined telluric and radio-wave at 6 bars, and the radio-wave at 1 bar, where in both cases the RX coil was tuned at the lower parallel mode to the transmitter frequency through adjustment of the coil wire length. Again in the previous 18m telluric experiment the proportion of telluric-wave to radio-wave at 10W was 0.7 mW : 0.55 mW, where both components are much closer and contributing approximately equally to the transmission of power from TX to RX, with only slight emphasis on the telluric-wave. In the 2 mile field location the ratio of signal strength telluric to radio is 5 : 1 which we can also conjecture may result from a more dominant LMD mode across the telluric cavity formed by the TMT system.

We do also need to consider the possibility that the radio-wave encountered significant obstacles in the 2 mile TEM propagation, reducing significantly the radio-wave component at the RX coil, but I would suggest that the combination of the two results regarding the better power transmission efficiency over the 2 miles distance than the 18m distance, the relatively close far-field distance, and the large signal strength ratio 5 : 1, could point towards a dominant LMD mode, and a preferential telluric transmission channel, over and above the TEM mode radio propagation channel.

In contrast at the 8 mile man-made reservoir location, although the signal tone could just be detected at 10W TX power, it was necessary to use up to 400W of TX power to get reasonable signal strength up to 4 bars. It was also noted that the ratio of telluric to radio-wave components was again around 1 : 1, and the far-field transmission distance had not significantly increased by going up to 8 miles at the transmitter frequency at the top-end of the MF band. It is considered here that the telluric channel/connection at the RX coil end was not as good as for 2 mile case, and especially in taking into account that the water-body used for the telluric ground was both man-made and may not be so well connected to the earth’s aquatic system. It is conjectured that the LMD mode was not established as dominant in the TMT transmission cavity, and that power reception at 8 miles was dominated by the TEM mode of far-field radio-wave propagation.

It must also be considered that the two field locations presented so far were not selected for any special water-table, river inter-connection, underground aquatic properties or channels, or for specific earth and rock type and composition. Both locations are in limestone regions and both are connected to water bodies, the 2 mile location being a natural river-fed lake, relatively close to the underground source of the river (a further 2 miles, so approximately 4 miles to the river source from the transmitter). The 8 mile location, being a man-made reservoir with a river tributary feed and outlet, is a further extension in the same direction from the transmitter. So the 8 mile location is essentially 6 miles further on from the 2 mile location, and 4 miles further on from the natural river-source of the 2 mile location.

Summary Conclusions and Next Steps

In this post, telluric transference of electric power has been explored and demonstrated in two different field locations in the near far-field region from the transmitter at 1.86Mc in the high MF-Band.  In both field locations signal strength could be measured at the transmit frequency in both the telluric-wave and the radio-wave at only 10W generator power. There was a vast difference in power required in each location to achieve approximately the same measured signal strength readings, 10W TX power with 6 bars at 2 miles, and 400W with 4 bars at 8 miles, with all other aspects of the TMT apparatus kept constant other than the field location telluric ground connection, and the over-ground terrain profile between the TX and RX. From the experimental results and measurements presented the following observations, considerations and conjectures are made:

1. The LMD mode is conjectured to be dominant in the 2 mile location based on the the large ratio between the measured telluric-wave and the radio-wave, and on considerations on telluric channel/cavity losses both for this experiment, and the previously considered 18m telluric channel.

2. The TEM mode is conjectured to be dominant in the 8 mile location based on the equal ratio of the measured telluric-wave and the radio-wave, and the large input power of 400W needed to get adequate measured signal strength, and on comparison with the very similar telluric experiment results in the 18m telluric channel.

3. The telluric connection quality to the earth through the type of water-body, is conjectured to be the most likely difference between the very different results of the two field locations. The difference in distance of 6 miles is not considered to be the major factor in the large difference in the location results.

4. The underground water inter-connection between the TX and RX is considered to have a significant impact on the quality of the telluric transmission medium between the two ground systems.

5. The impact of the earth soil and rock type and composition is as yet unknown on the telluric channel quality.

6. High losses will occur in the ground system to earth interface, and the telluric transmission channel/cavity with higher transmitter frequencies in the MF band. 1.86Mc appears far too high for any significant power transfer by the LMD mode in a telluric cavity.

7. Telluric transmission via the LMD mode is conjectured to be more efficient than by the TEM mode, and that with a sufficiently low frequency and a properly arranged LMD cavity in the TMT apparatus, it may be possible to transfer larger quantities of power in the far-field with better efficiency than could be accomplished using an overground wireless mode or radio-wave.

Next steps are to further explore Telluric Transference of Electric Power at different field locations both in the close far-field, and then at further distances from the transmitter, both at the same presented high MF-band frequency of 1.86Mc, and then at lower frequencies, and ultimately if possible down into the LF-band where Tesla was working with his own experiments. Lower frequency experiments present considerable challenges, including TMT size and scale, generator type and compatibility, radio regulation and licensing, availability of field locations, and resourcing and funding. If these challenges can be overcome then it may be possible to finally confirm or refute the possibility of high-efficiency telluric transference of power, and understand in much greater detail and accuracy the legacy that Tesla has left us to explore.

Click here to continue to the next part, looking at Telluric Transference of Electric Power – Brookmans Park AM Radio Transmitter.

1. A & P Electronic Media, AMInnovations by Adrian Marsh, 2019,  EMediaPress

2. Dollard, E. and Energetic Forum Members, Energetic Forum, 2008 onwards.