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
