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
