On 3 February 2011 09:13, Rik Strobbe <[email protected]> wrote:

Hello Roger,

 

 

congrats to you and G6ALB for this first succes.

At 3km you are still within the near field (at a wavelength of 33km), so the fact that the EFP works best might indicate that the transmit antenna acts as an "electrical antenna" rather than as a small loop.

If this is so the signal captured with the EFP will decrease with 40dB/decade, so if you have 20dB SNR at 3km you will reach 0dB SNR at +/- 10km (assuming same noise level). So if you could find a place "in the middle of nowhere" (where noise is low) at about 10km you might be able to copy something.

Another thought: how the EFP signal outside the house ? if the signal if much stronger inside the house this might indicate that the signal travels through the ground and is "brought up" by the house wirering and coupled into the EFP.

 

73, Rik  ON7YD - OR7T

 

 

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Van: [email protected] [[email protected]] namens Roger Lapthorn [[email protected]]
Verzonden: donderdag 3 februari 2011 0:39
Aan: [email protected]
Onderwerp: LF: More earth-mode tests and a puzzle

This evening, during further tests looking for G6ALB's earth-mode beacon signal on 8.76kHz, I discovered that best results receiving at my QTH 3km from Andrew were with a small E-field probe rather than a loop or earth electrode pair. With the EFP, signals could be detected in my upstairs shack with just a 19inch whip! This suggests that the electrostatic component is the dominant one rather than magnetic or simple potential difference measurable between the 2 earth electrodes. My basic physics is very rusty and any help clarifying what is going on would be appreciated. It now means we may have a much easier way of detecting utilities assisted earth-mode signals at greater ranges as the positioning of the EFP was far less critical than trying to detect signals with a loop lying on the ground.

Comments please?

73s

Roger G3XBM

Via my 2.4GHz handheld (iPod Touch 4g)