Paul,
There will be a benefit for you, so if it
is done easily, do it! When it can be done easily, why can't you bring up all
the L as high as possible?
Imagine the E-field lines that come out
of the antenna wire. You can imagine that by an analogical example:
A garden hose, in the form of the antenna
wire construction, with many holes in it. Imagine you have a
compressor on the bottom and connect the hose there. The water pressure
is equivalent to the voltage, the compressor has the function to increase the
pressure; the coil has the function to increase the voltage. The hose diameter
is assumed to be very big against the hole diameter so the pressure is almost
the same at each part of the hose (even at the end). Your goal is to bring as
much water (water [liters]is here equivalent to electrical charge
[As](absolute value)) as possible through the vertical part of the
hose without loosing to much on the way to the top. This is because, in
the electrical case, you want to fed as much current as possible through the
radiation resistance to radiate the power I^2*Rrad. The water (charge) that
comes out of the hose in the vertical part before reaching the maximum
vertical height is not crossing the upper part of the radiation resistance and
thus the ERP is smaller. So, it is the best to place the compressor/coil as
high as possible since if the pressure/voltage in the vertical section is
smaller (like before the compressor/coil) there is not so much water pressed
through the holes in the vertical section!
And if you increase the horizontal
section of the construction, there are more holes in sum above the compressor
and thus more water is pressed through them at a given pressure. So, the more
holes the more water, or charge (=current per cycle) in the vertical
part.
This analogical model can explain even
more but surely there are also things that cannot be compared (like a AC water
flow ;-); no closed circuit... ). But for a first imagination it is
useful in my point of view ;-)
If you place all the L on the tower it
will be optimal. Then, you could use a simple wire that connects to your earth
system without the need for a distance to other metallic parts, since
there is no HV on this wire any more! That makes it easier even more!
You can inject the power by applying a
isolated primary on the coil and connect it to your PA in the shack by a
loudspeaker cable. Or you need a transformer and inject it on the bottom of
the wire between earth and lower part of the coil. That may be even a litte
easier...
A later step will be to reduce the earth
resistance but you can do that after starting to come up on the band since
there will be no changes to the coil, maybe just to the output ratio of the PA
transformer. Which PA will you use?
Best 73 and much fun!
Stefan/DK7FC
Von:
[email protected] im Auftrag von Paul A.
Cianciolo
Gesendet: So 04.04.2010 22:28
An:
[email protected]
Betreff: LF: RE: W1VLF 9 Khz Antenna
update Putting inductance near the top.
Stefan
On page 60 and
61 of the Low Frequency Experimenters Handbook Peter Dodd RSGB there is
an example putting a coil near the top of the antenna
In this case
the transmitter is on 137 Khz and a of a portion (1/2) of the "L" needed to
resonate was moved near the top. According to measurements by Rik Strobbe
ON7YD an increase of 4 to 5 db was measured.
Do you think it
would be worth the effort to put 1/4 of the total "L" needed near the
top
I could do that
very easily.
PaulC
W1VLF
