Re: LF: VLF

[Roger Lapthorn <rogerlapthorn@gmail.com>]

Andy et al,

I tried this when I last experimented with "earth mode" conduction at 1kHz some 20 years ago. I used the central heating ground and a meat skewer at the far end some 10m away from the house. I was able to copy the keyed signal by ear some 300m away with minimal filtering on a second grounded electrode pair of meat skewers! I made no attempt to elevate the loop at either end. I could adjust the resistive match from 20 ohms to 150 ohms at the TX end but cannot remember the settings I used. I made no attempt to tune out any reactive part. The signal was also copied some 200m away in the middle of a field well away from wires,pipes and cables with a 5m base line and meat skewer grounds. Power was around 4W out from a small TDA2002 audio chip. This leads me to think that much further would be possible by "earth mode" with more power, larger base line spacing, elevated wire and QRSS.

All good fun.

73s
Roger G3XBM

On 8 March 2010 18:42, Andy Talbot <andy.g4jnt@googlemail.com> wrote:

...wishing I'd persued the NoV application a few years ago instead of just letting it slide into oblivion...

 

Has anyone yet tried a ground loop at 9kHz?   That was going to be my first (and probably only) antenna type, running a length of wire as far away from the house as I could get-away with and connecting it to a ground stake, then feeding this against the existing local earth.   I never got round to making measurements to see what sort of ground resistance might be expected, but that would have been a lot easier than winding 1.4H air wound chokes.

 

My house backs onto a main road, and there is a drainage ditch running behide trees and foliage running for about 70m in one direction that would have made a useful route to hide a wire in.  Might have been interesting hammering in a ground stake next to the footpath at the corner of the next road though !

Andy
www.g4jnt.com

2010/3/8 Wolfgang Büscher <dl4yhf@freenet.de>

Hi Stefan,

A VLF grabber would be very fine! If you can arrange that, it would perhaps be a motivation for the dreamers ;-)
 

Well there are two now (Markus' and Paul's) .. I will try to add a third but need to get away from the local QRM. The plan is to use an UHF FM link to the remote, battery-powered site but there are some issues to be solved - one of them is the lack of dynamic range of the FM transmitter/receiver, so I may have to add some analog bandpass filtering before the FM modulator (which would render it useless for broadband VLF signals, especially natural radio signals..).

Will keep you informed, when/where another VLF 'live spectrogram' goes online.

Cheers,
 Wolf .

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