To: | "[email protected]" <[email protected]> |
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Subject: | Re: LF: EbNaut from Todmorden |
From: | David Hine <[email protected]> |
Date: | Sun, 20 Mar 2016 08:45:48 +0000 (UTC) |
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Hi Paul. Interesting and I would like to know if you have any success with earth mode once the amplifier shutdowns have bee solved. (Some in field receiving may be interesting). It may be an unfortunate choice of the number of transformer primary turns that happens to be resonating as a series tuned circuit at 8 kHz and appearing as a short circuit to the amplifier? -add some more turns? -just a guess. Roger's ELF work is excellent and should be always used to 'get the feel' of ground communications. To have any real chance of success, megawatts are necessary, but this is not possible for most researchers. With very kind regards, Dave. From: Paul Nicholson <[email protected]> To: [email protected] Sent: Sunday, 20 March 2016, 7:39 Subject: Re: LF: EbNaut from Todmorden I found what I was looking for in Roger Lapthorn's notes on earth mode at https://sites.google.com/site/sub9khz/earthmode where he mentions that licencing is not required. However he is talking about earth mode where comms are via ground currents and there is no intended use of far field radiation. This is in contrast to an earth antenna where the ground current forms the lower leg of a vertical loop, such as is used by the military at ELF. Last night I fired up the amplifier and through the transformer was able to put about 600V RMS onto the wire, so about a kW into 380 ohms. The transformer worked very well but for some reason the amplifier kept wanting to do a thermal shutdown which is odd considering its 5kW average power rating. It's supposed to do 2.5kW average into a 1 ohm load. The test was at 8270.01 Hz but not even the faintest trace showed up on Gary G4WGT's spectrogram at 35km distance. Not surprising really, the ground around here is quite unsuitable as an earth loop: a metre or two of wet soil over the sandstone bedrock, the return current is not going to go deep. The transformer appears quite good at 8270 Hz and looks like it might work well at coupling power into the base of a VLF loading coil. The ground antenna has so far qualified itself as a nice high power dummy load. This evening I'll play a little more with it just to understand what the amplifier is doing but I don't think I'll continue much more with these earth experiments. David Hine wrote: > take care as the mains 'earth' Yes. Several years ago I experienced just that. I found, I think, about 40V between the domestic earth and a VLF antenna earth. Eventually I traced it to an electrical fault in a neighbour's tractor shed. The entire domestic ground of our little cluster of farms was at significant mains potential relative to a more distant earth ground. This might have gone unnoticed had I not been setting up a remote rx with its own ground. During a storm, nearby lightning could easily produce very large transient voltages between domestic ground and the ground of a remote antenna. I always disconnect everything on the approach of a storm. Right now, about 1.5V RMS at 50Hz between the ground 500m away and the house ground. It isn't unknown for farmers to run a single wire carrying live out to a distant shed with the return current via the ground. If anyone was doing that near here I would soon know about it! -- Paul Nicholson -- |
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