illrrrrrrW

Fig. 2. Parallel LC
network for I S/20m .
000
"
Fig. 3. L ne tw ork
(40/80m.)
While some equipment will load into a
line with a vswr of greater than 2 : I, most
manufacturers these days specify low vswr
to avoid such conditions as overheating of
TV sweep-tube final s and radiation of rf
from the transmitter cage. The answer for
some is to give up and try a more expensive
antenna, such as a trap vertical. But before
spending th ose dollars, why not try to do a
better job of matching than the coil can do
alone? This can be achieved by simply
adding a small variable capacitance at the
feedpoint, using clip leads to allow it to
fun ction as part of an LC network in series
or in parallel. Using an additional tap on
th e coil will allow the 52fl feed to be
matched more accurately.
The exact amount of Land C needed
for resonating and mat ching at a given
frequ ency will depend ma inly on the type
of mounting and ground system in use.
Before trying the matching network idea, I
found that a vswr of 2: I was the best
obtainable on several bands. On 15 meters,
the antenna was completely unusable with
a vswr over 3: 1. It was of course possible
to adjust the whip length for 15m, but
band-changing became a major chore.
After use of the,mat ching network, the
results were very satisfying. It was possible
to rea ch less than 1.3: I on all bands, and I
found that by proper pla cement of the coil
tap s I could go from 15 to 20m with just a
twist of C alone. This convenience was well
worth the effo rt.
Aft er matching with a standing-wave
bridge connected at the feed point, all I had
to do was mark the coil taps and positions
of C, and band-changing was now possible
in a matter of seconds. Besides all this, my
first QSO after the job was done resulted in
a good report from UA