[R-390] Balun for balanced antenna connector

[Vittorio De Tomasi]

> Message: 2
> From: "Richard Biddle" <theprof@texoma.net>
> To: <r-390@mailman.qth.net>
> Date: Sat, 6 Jul 2002 23:09:24 -0500
> Subject: [R-390] Balun for balanced antenna connector
> 
> 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.
> 

Been there, done that... I used an Amidon toroid for building a 200 ohm
balanced -> 50 ohm unbalanced transformer, and I found an easy way to
encase it. I got a 35 mm film can, and drilled a 5/8" hole on the bottom
of it. The twinax threaded part is inserted into the hole, and screwed
into the connector, so that the film can is kept firm between the
connector and the threaded parth. 
A RCA female connector is mounted on the cap of the can, and the
transformer is housed into the can.
I checked the device with my HP8640B and the guy has a very flat
response 0.5-30 MHz. I will put a photo of the device someday on my web
site, together with the modification I did to the input line filter of
my R390a....


vy 73


Vittorio ik2czl

-- 
*************************************************************************
Vittorio De Tomasi         ik2czl@amsat.org    http://www.detomasi.it
                                               http:/www.weaksignals.com

"Sometimes things just don't make sense, and that's just the way it is.
Live with it. More tea?" - Richard Feynman