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Roger
There are lots of places to experiment with so called
earth mode out in the countryside, it is not impossible, but if you live in
an environment that is swamped with a criss cross of buried cables and
pipes then this is not a hobby for so called earth mode
communications.
Strangely enough only a small % of the UK is swamped by
urban development. Most of the urban development is in concentrated areas and
there are vast areas of undeveloped wide open spaces. From what you say you
are in a hostile urban swamp and if you are serious about VLF I think you would
need to move, comfortable as you might be otherwise
As regards the question about launching a respectible
signal on LF/VLF then its simple, Plenty of power and an Elevated
antenna.
de G3KEV
I
----- Original Message -----
Sent: Thursday, February 03, 2011 5:12
PM
Subject: LF: Earth-mode or not
earth-mode
Thanks for feedback and questions from Rik, Chris, Mal, Stefan
and others on and off this list.
I'm still waiting for someone to
explain to me why, if this is (mainly) conduction along metal pipes, which I
am sure it is, best results are not obtained with a galvanic connection
to the pipe at each end and why best receive results are with an E-field
probe. I remain puzzled. Answers please!
May I reply on a few
general points raised by some?
What is the definition of
earth-mode?
I could not find one, but my understanding is
"communication between two points essentially using conduction through the
ground". In the modern world it is almost impossible to find anywhere,
except remote moors, that is not criss-crossed with buried cables and pipes.
My interpretation of earth-mode therefore includes utilising these as a means
of helping a signal get from (a) to (b). Hence my term "utilities assisted
earth-mode". In mining and military use of earth-mode I think this is also
accepted. What I also mean is communicating from (a) to (b) not using a
radiated signal or induction as the prime means of propagation.
Why experiment with this form of VLF/ULF communication?
From my tests last year it was clear that local communication
"piggy-backing" on these buried utilities seemed to be possible over many
kilometres without the need for large and complex antenna systems that are
essential to get even a tiny VLF signal actually radiated, as Ossi,
Gerhard, Stefan and Chris know only too well.
Questions I'm trying to
answer are:
- How best to launch a signal?
- What in the ground (apart from water, soil and rock) helps the signal
get from (a) to (b)?
- What works best to pick up the VLF/ULF signal at the far end of the
link?
- What frequencies work best?
- What are the noise sources and how can these be minimised?
- How close to buried utilities does one really have to be for it to work?
- Can one use rivers, canals or the sea coast for earth-mode?
- How little/much power is needed for a given range?
- What modes are most effective?
- What is the practical range limit?
- Is there a practical use for this form of
communication?
Also, I'd welcome suggestions
for further practical tests. A lot of the
experience is directly useful in the reception of DX radiated VLF
signals.
Results have been shared here
because others are known to be interested in this aspect of VLF work, but if
people think the LF-reflector is not the right place please say so.
73s
Roger G3XBM
--
g3xbm-qrp.blogspot.com/
www.g3xbm.co.uk
www.youtube.com/user/g3xbm
G3XBM GQRP 1678 ISWL
G11088
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