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LF: 8.97kHz - Near field and radiated signals?

from [Roger Lapthorn] [Permanent Link][Original]
To: [email protected]
Subject: LF: 8.97kHz - Near field and radiated signals?
From: Roger Lapthorn <[email protected]>
Date: Mon, 24 May 2010 11:13:28 +0100
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Please can "experts" offer me some advice? This is all stuff I should know, but have either forgotten or never properly understood in the first place. Excuse my ignorance but I'm getting a bit thick in my old age.

As you know, I'm testing out some near field kit using grounded electrodes and loops.  Presently, I'm transmitting with a grounded electrode pair and 4W and experimenting with reception at a distance (up to a few kms) using grounded electrode pairs, voltage probe antennas and loops. At the distances I'm covering so far (not very far) I am well within the reactive near field. I hope to try replacing the grounded electrode pair at the TX end with a large single turn loop to see how signals compare.

My questions are these:
  1. From an electrode pair transmit "antenna" connected by a slightly elevated wire a few metres average above ground what sort of signal is emitted? Am right in thinking that conducted, inducted and radiated signals are all present? Is this true for a single turn loop too?
  2. Is there a simple formula that will calculate the strengths of each of these types of signal?
  3. At short range (up to 1km or so) what sort of receive antenna is likely to give best results - loop, probe, grounded electrodes?
  4. Is the tiny radiated power from such a modest set-up (if essentially there at all) likely to be detectable more than a few kms away? I appreciate that signals should attenuate by 18dB every time distance is doubled with induction, but presumably a very tiny radiated signal (if there) would attenuate as per RF theory at 6dB per doubling distance, so a weak radiated signal has a better chance of getting a bit further.
Now, I shall no doubt get more answers to all of these questions by continuing my tests, but some pointers from experts would be helpful. Clearly I know that with huge antennas and lots of power (as in Stefan's case) signals are detectable, just, at great range. I guess I'm after some "calibration of possibilities" with much more modest stations and power. It's all certainly most fascinating.

73s
Roger G3XBM

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