20s receivers antenna impedance

Glen E. Zook gzook at HOME.COM
Sun Nov 18 22:28:22 EST 2001

I have a collection of over 100 restored receivers from the 1920s
through the 1950s (mostly 20s and 30s) and, frankly, I wouldn't want to
even try to come up with a "nominal" value for antenna impedance.  Most
of them do work very well with the single-wire antenna.

You might try and use a TV type balun (i.e. $1.95 from Radio Shack) if
you only have 50 ohm feed antennas.  The balun should be connected with
the "twin lead" going one side to the antenna connection and the other
to ground.  You then connect the coax to the type "F" connector.

TV baluns have to go down to at least 5 MHz and, according to a friend
of mine who was in the cable TV business for over 30 years, most make it
into the broadcast band with no problems at all.

On the "boat anchor" receivers that were designed with the two terminal
antenna connectors (plus ground) use of a TV balun really "perks up" the
receiver when using a coax fed antenna.  On later models that were
designed for 50 ohm coax, they don't help at all!  Just make sure and
disconnect the "jumper" from one side of the antenna terminals to ground
before installing the balun.

I do know that all of my anitque/vintage receivers work pretty well
using antenna lengths of twenty feet or less.  Of course, hooking up
more wire definitely helps pull in the "DX" broadcast stations.  The old
TRF sets are actually fairly sensitive considering the design.  The
really old superheterodyne receivers (i.e. Radiola VII and AR-812 from
about 1924) are not that sensitive.  Older regenerative sets like the
Crosley 51 are pretty sensitive if adjusted correctly.

Glen, K9STH

--- Steve Gill <sgill at palouse.com> wrote:

Was asked what a typical impedence would be for the antenna input on the
old broadcast band sets of the 1920s.  My memory from childhood is that
most of the antennas were end fed random length wire (e.g., distance to
the furthest tree from the house and the like), so probably had quite a
bit higher impdence than the 50 ohms prefered by modern rigs, and
probably had a bit of reactance as well.  But, if one could provide the
ideal impendence, what would it be??

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