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Chris and LF
This is the point I have been making for some time,
Experimenting with so called earth mode in an urban environment with a network
0f underground pipes and cables of various varieties is a meaningless excercise.
The experiment needs to be conducted in a wide open rural
environment with earth rods used at both the Transmit and Receive
end.
de mal/g3kev
----- Original Message -----
Sent: Thursday, February 03, 2011 11:01
AM
Subject: Re: LF: RE: More earth-mode
tests and a puzzle
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
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