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LF: Earth mode tests (8.76kHz)

from [Roger Lapthorn] [Permanent Link][Original]
To: [email protected]
Subject: LF: Earth mode tests (8.76kHz)
From: Roger Lapthorn <[email protected]>
Date: Fri, 10 Dec 2010 13:53:58 +0000
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Today I did a test receiving my 8.76kHz QRSS3 VLF signal 5.1km away from the home comparing reception using (a) an 80cm loop antenna and (b) a small earth electrode antenna (14m spacing) using a variety of pre-amps.  Although quite solid reception (17dB S/N in 0.18Hz BW) was achieved using the loop laying flat on the ground, there was absolutely nothing detected using the earth electrodes which were pushed into the soil either side of the road, which was both surprising and disappointing. I used the very same pre-amp in both cases and also tried the lo-Z input 8-9kHz tuned pre-amp with the earth electrodes that successfully copied DK7FC at 648km last weekend on the earth electrodes at home.

Several possibilities for the failure with the earth electrodes at the RX site:
  • The electrode spacing was far too small
  • The barbecue skewers used as RX electrodes were too short and not making decent soil contact
  • The soil was too wet, so the pick-up (effective loop area in the ground) was lower than with dry, low conductivity soil; the test site is in the fens where the soil is a dark peat.
Next step is to repeat the test up on the chalk uplands to the south of the QTH at about 4km distance where soil conductivity will be lower and to try a larger earth electrode spacing on receive.

When compared with the 2873km DX by Stefan this is nothing to get too excited about, but fun experiments nonetheless.

73s
Roger G3XBM

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G3XBM   GQRP 1678    ISWL G11088

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