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Hi Roger,
Well, in my humble opinion you're use of 'earth'
mode and so on is inaccurate. I think you have proved this more than once with
your lack of results using your earth rod/house pipes! it seems to me this is
simply conduction through underground pipes and wires. Not totally unexpected.
Genuine earth mode would require you to be away from all pipes etc. and using
two earth rods at both ends.
Whilst this is interesting, I am not sure if it is
anything new or unexpected, or repeatable in open countryside. Keep up the
experimenting though! We're all keen to see what you try next!!
Vy 73,
Chris, G4AYT, Whitstable, Kent, UK.
----- Original Message -----
Sent: Thursday, February 03, 2011 10:35
AM
Subject: Re: LF: RE: More earth-mode
tests and a puzzle
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 <[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
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)
--
g3xbm-qrp.blogspot.com/
www.g3xbm.co.uk
www.youtube.com/user/g3xbm
G3XBM GQRP 1678 ISWL
G11088
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