Howdy All,
This is my first message on the TOPBAND reflector and I sincerely need
some easy to understand help on how to go about making tuning/matching
coils. Just pretend that I'm basically illiterate and need some really
simple to follow instructions.
To back up a little, P. Smith (N6SS/MM) visited my QTH and eyeballed
the roof of my building and one he got back to AZ he sent me a design
for a 160M antenna built to the layout of my roof. I am going to quote
some of the stuff he said, now remember I am not asking for a Critique
of what he said, just how to make the coils.
"Initially wind the coils with #14 or #16 bare copper wire. It is easy
to work with. Set the taps for minimum SWR on the radials and for
resonance and minimum swr on the radiator. Measure the inductances with
the LCR meter, then duplicate each coil with new coils formed from 1/4"
copper tubing. The radiation resistance of this verticalis only a few
ohms and reactance and RF currents are very high. Large coils with large
conductors are essential to reduce losses.
I'd suggest to start with the radials first as that is the easiest
part of the project and as important as the radiator. run a pair from
corner to corner of the parapet. These radials are "fat" and from a
bird's eye view look like a pair of airplance propes. This is to reduce
the reactance theryby requiring smaller loading coils. (((THIS I
UNDERSTAND))). Start with the coils shorted. ((HOW IS THIS DONE)). Feed
the pair like a dipole ((????))))) Sweep with the analyser and find the
freq of lowest swr. Then add an equal number of turns to each coil a
bit at a time unitl the radilas resonate on 1830KHZ.
The radiator is a 40ft mast with four 35ft toploading wires.
Insulated at the base and mounted about level with the parapet. Elnec
says the resonant freq is around 3 Mhz. The large coil from the base of
the mast to the radials serves to resonate at 1.83 Mhz and match to the
50 Ohm feedling. Make the final coil of 1/4 in copper tubing 6 to 8 in
in diameter and only 1.5 - 2 turns per inch. Adjustments are touch so
it is best to bring the clip leads thru the center of the coil makeing
it easy to move the taps a fraction of a turn. After final matching
solder the taps in place"
Now i guess I had better let you know that I am A92GD and would like
very much to get some TOPBAND activity generated from this QTH. Any help
you can provide would be greatly appreciated.
Thanks in Advance
73,s
A92 GOSH DARN
Bob
(Bob Frick)
US Embassy
Manama, Bahrain
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