Re: LF: RE: More earth-mode tests and a puzzle

[Roger Lapthorn <rogerlapthorn@gmail.com>]

Hi Rik,

I am pretty certain the signal is flowing along the water pipes but that the field around the pipes is much better detected with the E-field probe than with the loop. The EFP works very well outside in the street too and is far less critical about position and orientation. With the loop the signal is strong when clearly over the pipe work, whereas with the EFP one can, it seems, be almost anywhere in the road and house and get a signal. In the house I presume I am picking up the same sort of signal surrounding the pipes within the property.

What I do NOT understand is why I get ZERO signal pick-up from G6ALB at 3km with another earth-electrode set-up at the RX end. One of my ground points is the copper central heating radiator which connects directly to metal pipes in the road. I know this as I use the same set-up to launch my own earth-mode signals that can be detected in the roads with a loop out in the fens >5km away. Logic tells me that if Andrew G6ALB is launching his signal along pipes from his earth electrode pair then I would get strongest signals by also connecting one ground to the metal pipework at the RX end, but this is definitely not the case as there is absolutely no signal detectable in QRSS3 by this method, but at least 20dB S/N with the EFP! Can someone explain what is going on please as I am very baffled!

Tomorrow both G6ALB and I will put our beacons on (me on 8.7608kHz and G6ALB around 8.755kHz) and I will take a trip out into the fens with both the loop and the E-field probe to see what I detect. It is possible that with the EFP I may be able to detect the signal(s) at greater range than ever before on 8.76kHz.

Incidentally, the pipe tracing papers I have read suggest that viewing the pipe as a conductor with a distributed capacitance to ground along its length lower frequencies will propagate further as the losses from this distributed capacitance to ground will be lower. This ties up with my own observation that signal levels at 5.3km distance are MUCH stronger on 0.838kHz than at 8.76kHz. I have still to try detection with an EFP at 0.838kHz.

I really want to get on with my 4m transverter, but this VLF earth-mode stuff has become rather absorbing and time consuming. Having G6ALB locally also TXing now has added to the fun and ability to do meaningful experiments.

By default we seem to have a band-plan for the Dreamer's Band: earth-mode around 8.76kHz and radiated around 8.97kHz.

73s
Roger G3XBM

On 3 February 2011 09:13, Rik Strobbe <Rik.Strobbe@fys.kuleuven.be> 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: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.org] namens Roger Lapthorn [rogerlapthorn@gmail.com]
Verzonden: donderdag 3 februari 2011 0:39
Aan: rsgb_lf_group@blacksheep.org
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)

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