10 Mar 2014
15m earth-electrode
Well, because of my stroke and bad weather, a few days ago was the first chance I had to go into the garden to inspect the far grounded electrode. To my great surprise I discovered my wire was not connected to the ground rod at all and was as my son had left it last September - the wire was just connected to a rolled up piece of coax laying on the ground, in effect a capacitive ground connection: that was why I needed series inductance then! The feed wire is about 1.5m off the ground along a fence. Since the start of the weekend I have been using the far end grounded (as I thought it was originally) to the ground stake. Impedance is still very high (around 200-300 ohms) but I no longer need the series inductance. As for results, it seems perhaps more directional and (maybe) a few dB down on the previous (unintentional) arrangement. Whether the antenna was working as an NVIS wire is not clear but at the old QTH running the wire back through the grass made little or no difference to performance of the earth-electrode antenna, confirming the " loop in the ground" behaviour at MF/LF. I may next try extending the poorly grounded wire further along the fence top to compare performance. The maximum run possible is about 30-35m.
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3 comments:
Hi Roger,
I am glad you found this! I was feeling quite disappointed that I had not managed to hear anything from you via my own earth loop system, despite your reservations on me being too far away. I shall listen out with renewed vigour once you have connected it up again. I did spot you on 80m a while ago, but I guess this was by radiated wave.
Glad to hear you are getting out and about now.
73 Ken G4APB.
Ken, if you were looking around 8.27kHz I am not at all surprised. VLF needs special techniques: frequency locking using Spectrum Lab software, incredibly narrow bandwidths (47-470uHz typically) and even then a low noise environment to even see a small trace after HOURS of looking, Casual listening will NOT work at VLF! At 472kHz a 15m earth electrode "antenna" should detect WSPR signals with suitable time syncing and software. In the last few days I have spotted 3 German stations with mine using 15m earth electrodes and an unmodified FT817. BTW, the propagation modes at 136 and 472kHz is through the air with the ground loop launching a signal. With VLF earth-mode the main short range mode is utilities assisted (propagation assisted by buried pipes and cables). I have copied most EU VLF amateurs out to about 1000km by true radiation, but my own eartb-mode signal has not been copied beyond 6km.
Hi Roger, thanks for the reply. I was listening on 8.97khz as per your blog but I guess you have now QSY'd to the new freq of 8.27KHz. The problem I see with using your method of plain QRSS is not much information is sent and the identity method is MK 1 eyeball and not electronic. Reading up on WSPR-X-15 mode with its' narrow BW, I did wonder how this compares to QRSS and was keen to give it a try in earth mode at VLF. What settings do you use to set Spectran to give such narrow BWs and on 8.27KHz?
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