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Date: Mon, 24 May 2010 11:13:28 +0100
Message-ID: <AANLkTinG-0mJJ3CDqFwxeLXfOJXFFfs42gjLYz8yX3rW@mail.gmail.com>
From: Roger Lapthorn <rogerlapthorn@gmail.com>
To: rsgb_lf_group@blacksheep.org
DomainKey-Status: good (testing) 
Subject: LF: 8.97kHz - Near field and radiated signals?
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Please can "experts" offer me some advice? This is all stuff I
*should*know, but have either forgotten or never properly understood
in the first
place. Excuse my ignorance but I'm getting a bit thick in my old age.

As you know, I'm testing out some near field kit using grounded electrodes
and loops.  Presently, I'm transmitting with a grounded electrode pair and
4W and experimenting with reception at a distance (up to a few kms) using
grounded electrode pairs, voltage probe antennas and loops. At the distances
I'm covering so far (not very far) I am well within the reactive near field.
I hope to try replacing the grounded electrode pair at the TX end with a
large single turn loop to see how signals compare.

My questions are these:

   1. From an electrode pair transmit "antenna" connected by a slightly
   elevated wire a few metres average above ground what sort of signal is
   emitted? Am right in thinking that conducted, inducted and radiated signals
   are all present? Is this true for a single turn loop too?
   2. Is there a *simple* formula that will calculate the strengths of each
   of these types of signal?
   3. At short range (up to 1km or so) what sort of receive antenna is
   likely to give best results - loop, probe, grounded electrodes?
   4. Is the tiny radiated power from such a modest set-up (if essentially
   there at all) likely to be detectable more than a few kms away? I appreciate
   that signals should attenuate by 18dB every time distance is doubled with
   induction, but presumably a very tiny radiated signal (if there) would
   attenuate as per RF theory at 6dB per doubling distance, so a weak radiated
   signal has a better chance of getting a bit further.

Now, I shall no doubt get more answers to all of these questions by
continuing my tests, but some pointers from experts would be helpful.
Clearly I know that with huge antennas and lots of power (as in Stefan's
case) signals are detectable, just, at great range. I guess I'm after some
"calibration of possibilities" with much more modest stations and power.
It's all certainly most fascinating.

73s
Roger G3XBM

-- 
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/g3xbm
G3XBM    GQRP 1678      ISWL G11088

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Please can &quot;experts&quot; offer me some advice? This is all stuff I=
 <i>should</i> know, but have either forgotten or never properly understoo=
d in the first place. Excuse my ignorance but I&#39;m getting a bit thick=
 in my old age.<br>
<br>As you know, I&#39;m testing out some near field kit using grounded el=
ectrodes and loops.=A0 Presently, I&#39;m transmitting with a grounded ele=
ctrode pair and 4W and experimenting with reception at a distance (up to=
 a few kms) using grounded electrode pairs, voltage probe antennas and loo=
ps. At the distances I&#39;m covering so far (not very far) I am well with=
in the reactive near field. I hope to try replacing the grounded electrode=
 pair at the TX end with a large single turn loop to see how signals compa=
re.<br>
<br>My questions are these:<br><ol><li>From an electrode pair transmit &qu=
ot;antenna&quot; connected by a slightly elevated wire a few metres averag=
e above ground what sort of signal is emitted? Am right in thinking that=
 conducted, inducted and radiated signals are all present? Is this true fo=
r a single turn loop too?<br>
</li><li>Is there a <i>simple</i> formula that will calculate the strength=
s of each of these types of signal?</li><li>At short range (up to 1km or=
 so) what sort of receive antenna is likely to give best results - loop,=
 probe, grounded electrodes?</li>
<li>Is the tiny radiated power from such a modest set-up (if essentially=
 there at all) likely to be detectable more than a few kms away? I appreci=
ate that signals should attenuate by 18dB every time distance is doubled=
 with induction, but presumably a very tiny radiated signal (if there) wou=
ld attenuate as per RF theory at 6dB per doubling distance, so a weak radi=
ated signal has a better chance of getting a bit further.</li>
</ol>Now, I shall no doubt get more answers to all of these questions by=
 continuing my tests, but some pointers from experts would be helpful. Cle=
arly I know that with huge antennas and lots of power (as in Stefan&#39;s=
 case) signals are detectable, just, at great range. I guess I&#39;m after=
 some &quot;calibration of possibilities&quot; with much more modest stati=
ons and power. It&#39;s all certainly most fascinating.<br>
<br>73s<br>Roger G3XBM<br><br>-- <br><a href=3D"http://g3xbm-qrp.blogspot.=
com/">http://g3xbm-qrp.blogspot.com/</a><br><a href=3D"http://www.g3xbm.co=
.uk">http://www.g3xbm.co.uk</a><br><a href=3D"http://www.youtube.com/user/=
g3xbm">http://www.youtube.com/user/g3xbm</a><br>
G3XBM =A0 =A0GQRP 1678 =A0 =A0 =A0ISWL G11088<br>

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