[R-390] Balun for balanced antenna connector

[Richard Biddle]

It seems to me that a balun on the balanced antenna connector would be a
better way to feed the R-390 and still get the benefit of the extra stage in
the RF deck.  Being a frugal type (cheap) I decided to kludge something
together.

I removed the 75 ohm to 300 ohm balun from one of the "transformers" that
come with most VCRs (a 1" x 1/2" x 1/2" with an F-connector and two screws).
I figure 300 ohm to 75 ohm should be close enough for government work.
Rather nicely built.

I used an Amphenol 82-5589 twinax connector.  I sawed the threads from the
RG-58 UG-175/U reducer used for PL-259 connectors.  I soldered this into the
back side of the twinax connector.  I was able to fit the balun into the
connector and ran RG-58 to the antenna switch box.

I have not run any objectives tests on this, but it does seem to help reduce
the hash picked up inside the shack.  The signal generator in the shack with
a whip on it seem to generate a stronger signal on 10.5 MHz then when I ran
an unbalanced antenna into the balanced connector.

I'm not sure how well this tiny thing would do on the low end of things, but
it seems to work prety well.

Speaking of Hammarlunds, I saw an HQ-145X go for US$560 on ebay a couple of
weeks ago.  It looked just like the one sitting on my shelf.  Hmmm, I wonder
if I can figure out how to trade it for a Model 1911A, say a Colt or Kimber
:)

73 de Richard, KB5WLH



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