"Art Unwin KB9MZ" wrote in message
m...
I doubt that the coil will have a Q of more than 300 if that !
Art





"Frank" wrote in message
news:JCe1d.97059$jZ5.12695@clgrps13...
"denton" wrote in message
...
Hi all...
I am starting to work on something to use on 160 thru 20 meters.
I currently have an aluminum mast that is 32 ft long with a small cap
hat
on
top.
the antenna will sit in the center of an area approx 50 z 50'
(backyard).
I
plan to put down 40 plus radials, the majority which will be situated
to
radiate out from the base of the vertical.
some will meander along the house foundation and property line..
I plan on also tying in the galvanized (not chain link) fence around
the
back yard to the radial system, as well as the house plumbing.
40 meters should be direct feed.
I will homebrew a matching L network for use on 160 thru 60 meters.
I will also try a 20 meter tuning stubb.
Does anyone know what the size of the loading coil that MFJ uses in
their
80
& 40 meter vertical?
I have read of just about everything I can find online of this sort of
project and have played with Eznec demo a bit and think this will be a
doable project.

Also the series inductor should have a very high Q for 160 m. A Q of
1000
will loose about 30% of your power.

Frank

Based on Terman's "Radio Engineers Handbook" dated 1943, pp 31 - 53. I have
written a program In MathCAD Pro, which indicates a coil made from 1/4"
copper pipe, 12" long, and 3 inches diameter has an inductance of 39 uH and
a Q of 1132 at 1.8 MHz. (6" in diameter and 24" long shows a nominal Q of
1600). To be honest I have never built such a coil, and it would probably
be very difficult to measure. I agree that typical "Airdux" coils have a Q
in the range of 300 or so.(Silver plating, or gold, would also be desirable
to prevent lossy copper oxide build up). Anyway if you are interested I
can send you the MathCAD file. I would be very happy if somebody could check
my math. It think the point I was trying to make it that electrically short
antennas have such a low real input impedance that building an efficient
matching network is challenging to say the least. Even if such networks are
feasible the huge voltages developed at the base could prove to be a
problem.

73,

Frank