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
wavelength, 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 9kHz 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 currents etc) and 2.5kW will be
needed.
73, Rik ON7YD
________________________________________
Van: [email protected] [[email protected]]
namens Alan Melia [[email protected]]
Verzonden: woensdag 28 april 2010 16:57
Aan: [email protected]
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 hung
their loops in the trees. Will it work at 9kHz ?? Probably have to try it to
see......
Alan
G3NYK
----- Original Message -----
From: "Rik Strobbe" <[email protected]>
To: <[email protected]>
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 bottom
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 reduce
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 from
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
|
