From: Rik Strobbe <Rik.Strobbe@fys.kuleuven.be>
To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
Date: Wed, 28 Apr 2010 17:27:12 +0200
Thread-Topic: Re: RE: W1VLF 8.97 KHz UPDATE  Trees,  Questions, Ground
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Subject: LF: RE: Re: RE: W1VLF 8.97 KHz UPDATE  Trees,  Questions, Ground
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Hi Alan,

indeed, "low voltage" loops suffer far less from these losses.
But the radiation resistance of a loop falls with the 4th power of the wav=
elength, whereas for a vertical it is only with the 2nd power.
At 9kHz a loop of 15m high and 40m long will have a radiation resistance=
 of merely 10 nanoOhm (on 137kHz it is 0.5 milliOhm). So get out 1mW on 9k=
Hz one would need to pump 330A into the antenna. Using 1cm diameter solid=
 copper wire for the loop (anything less will probably act as a fuse) the=
 loss resistance is at least 0.025 Ohm (just copper loss, no stray current=
s etc) and 2.5kW will be needed.

73, Rik  ON7YD

________________________________________
Van: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.or=
g] namens Alan Melia [alan.melia@btinternet.com]
Verzonden: woensdag 28 april 2010 16:57
Aan: rsgb_lf_group@blacksheep.org
Onderwerp: LF: Re: RE: W1VLF 8.97 KHz UPDATE  Trees,  Questions, Ground

Rik ....Reduce the effect of the trees?? How about reducing the voltage on
the antenna?? this is effectively what the loopers did on 136 and then hun=
g
their loops in the trees. Will it work at 9kHz ?? Probably have to try it=
 to
see......

Alan
G3NYK

----- Original Message -----
From: "Rik Strobbe" <Rik.Strobbe@fys.kuleuven.be>
To: <rsgb_lf_group@blacksheep.org>
Sent: Wednesday, April 28, 2010 3:31 PM
Subject: LF: RE: W1VLF 8.97 KHz UPDATE Trees, Questions, Ground


Hi Paul,

Looking here  http://rescueelectronics.com/9-Kilohertz.html near the botto=
m
of the page one can see that the tower is backed up by forest.
I wondered how much, if any,  effect on antenna current running a long
radial out in the forest would have?

It might increase the loss resistance.

It is a kind of trade-off: one the one hand more "area coverage" will redu=
ce
the loss resistance (cfr. Laurie's footprint theorie) on the other hand
coming close to or even going over any greenry will cause an increase of=
 the
loss resistance.

If it isn't too much trouble: just try and measure

A) Am I just giving the trees a better return path or  ground connection
(the radial)  to the coil???
And the power is being eaten up by the trees???
OR
B)  Is there a chance this power is actually being radiated, and therefore=
 I
should pursuit accumulating these grounds, and their current and return it
to the coil??

The only way to avoid that power is "eaten" by the trees is staying way fr=
om
them (or remove them).

Apart from than there is little you can do. Or maybe trow wires over the
tree and connect these wires to the ground system (not very practial I'm
afraid).

But, with or without trees:, the better the ground system (rod's) the more
efficient the antenna will be.

What is a tree at 9 KHz???
A very lossy capacitor ?

73, Rik  ON7YD - OR7T