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
