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| Subject: | LF: 8.76kHz earth mode tests today |
| From: | Roger Lapthorn <[email protected]> |
| Date: | Thu, 13 Jan 2011 20:25:55 +0000 |
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Today being mild and dry (and less muddy) for the first time in almost 6 weeks, I decided
to do a field test with my improved 8-9kHz tuned preamp and loop
antenna. A 5W QRSS3 "earth mode" (through the ground) test signal was
emitted using my 20m spaced earth electrode pair on 8.760kHz from the
Burwell QTH. I ventured out into the countryside armed with the 80cm
loop and preamp to see where the signal could be copied. In addition to
my usual test sites at 1.6 and 5.1km I tried other directions and sites
today. A map showing where signals were/were not received is attached together with a screen shot taken at 4.75km west of the TX. The signal does seem to travel along the METAL water pipes, which must be absent to the east of the QTH beyond the village, where I assume they must be plastic, at least in places. No reception away from roadsides was attempted. Reception is definitely not as good at 8.76kHz as it was at 0.838kHz but this could be because the ground was saturated with rain from the last few days, or perhaps because sections of pipes have been mended with plastic pipes since last summer. Ideally I'd like to repeat the tests in dry weather on 8.76kHz and on frequencies around 6, 4, 2 and 1 kHz (avoiding mains harmonics) to see how signal levels compare. Last summer the earth mode signal at >5km was so strong in places on 0.838kHz that 10wpm CW was copyable by ear. Signal levels must be around 10dB weaker at 8.76kHz than on 0.838kHz. These tests are not in the same class as the radiated DX being achieved by several stations now, but I know some on this list are interested in these rather less earth-shattering experiments. Also, it is the sort of experiment that anyone can undertake without great expense or effort. I question whether an NoV is strictly needed considering the signal radiated must be in the pW region. 73s Roger G3XBM -- g3xbm-qrp.blogspot.com/ www.g3xbm.co.uk www.youtube.com/user/g3xbm G3XBM GQRP 1678 ISWL G11088
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