LF: 136kHz QRP with earth electrodes: 14.9km DX on QRSS3 today

[Roger Lapthorn <rogerlapthorn@gmail.com>]

Hi everyone,

This morning I did some more tests using my little 136.93kHz 2W QRSS3 beacon feeding into the 20m spaced earth electrodes. The TX end was unchanged, but this time on receive I used my 30t 80cm loop resonated with about 700pF and fed straight into the high impedance input of my E-field probe.

Results were as follows:

• At 2.4km good copy by ear (12wpm CW would have been very solid)
• At 8.6km good copy using Spectran
• At 14.9km clear copy of my callsign and locator in QRSS3 with Spectran on the Gog Megog Hills near Cambridge (see screenshot)

All these locations are more or less in the line of the earth electrodes that run NE-SW from the home QTH (JO02dg).  Another RX test some 11km to the south of the QTH  resulted in no visible trace, suggesting the TX earth electrodes are behaving as a loop antenna with some directionality. This was not the case when the same earth electrodes were used at 0.838kHz some weeks ago and when the mode was mainly conduction through buried utilities.

Remember, this is ultra simple stuff:

• A 2W out crystal controlled QRP 136kHz beacon TX on a 5 x 5cm board (see picture)
• An invisible ground "antenna" that cannot be seen, even when a few metres away from it.
• No attempt whatsoever to match the TX to the earth electrodes.
  
• A simple loop and FET impedance matching circuit and deaf FT817 at the receiver end.

It would be interesting to work out what the ERP must be. Can anyone estimate this please based on the QRSS3 trace on Spectran at just under 15km?  I was using 0.17Hz resolution and 11025Hz FFT sampling rate.

Interesting to speculate what would happen with such a system at 73kHz. Pity there is no allocation there today.

73s
Roger G3XBM

[PS well done to Stefan on the sub-9kHz tests yesterday.]

-- 
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G3XBM   GQRP 1678    ISWL G11088

2w_beacon_020810.jpg
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gogs_ee_2w_loop_summary.jpg
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