[Hallicrafters] Substitute antenna coils

[Glen Zook]

The easiest "fix" that I have found for the impedance
mismatch is to use a TV balun coil.  They have to make
it down to at least 5 MHz for various CATV signals,
and, according to a friend of mine who has had many
years in the CATV and cable TV business, virtually all
of them make it into the broadcast band without any
problems.

Make sure and take loose the jumper that is placed
from one of the antenna terminals to ground.

The TV balun works wonders on receivers like the
Collins 75A-1.  I have used them on various receivers
including the Hammarlund HQ-140X, Hallicrafters S-85,
SX-100, and S-107, and on other brands as well.

The use of a tuner works fine.  However, you have to
retune it whenever the frequency excursion is very
great.  I had a home brew tuner on the 75A-1 that I
owned in the late 1960s. It worked fine, but I had to
retune it all the time.  The TV balun works across the
entire frequency range of the "boat anchor"
communications receivers.

I have measured (using one of my three service
monitors) apparent "gains" of from 6 dB to over 20 dB
between a direct feed of 50 ohms and the use of a TV
balun.  My Collins 51J-2 (.5 to 30.5 MHz in 30 1 MHz
ranges) improves from almost 10 dB to over 22 dB
depending on the band.  Most of the Collins 51J series
have an antenna impedance of 400 ohms as does the
75A-1.  The same thing goes for virtually all of the
older receivers that have the three terminals (two for
antenna and one for ground).  Most of them have input
impedances of between 300 and 400 ohms with a few as
high as 600 ohms and as low as 200 ohms.

The TV balun is not a "perfect" match.  However, the
input impedance of a general coverage receiver will
vary somewhat with frequency.  Thus, a TV balun is a
good compromise.

You have to either get an adapter to go from the Type
"F" female on the balun to a "normal" type of coax
connector (an "F" to BNC is the most common and the
cheapest) or put a type "F" (available from Radio
Shack and other places) on the end of a piece of
RG58/U.

According to my friend, the TV baluns cost the CATV
companies less than 20 cents each.  However, you will
have to pay from $2 to $3 if you have to buy one from
most places.  But, they come with all sorts of things
like VCR, DVD player, etc.  Many amateurs have several
around the shack from these video accessories.

Anyway, the use of a TV balun does work, requires no
modifications to the receiver, and is fairly cheap.

Glen, K9STH


--- Al Parker <anchor at ec.rr.com> wrote:
Yes, it very definitely helps a rcvr to have a
matching sytem between it & the antenna.

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