[R-390] antennas

[Roy Morgan]

At 09:31 AM 10/17/2007, Rasputin Novgorod wrote:
>Hi Guys:
>
>My random wire connects via a 9:1 un-balun to 50 ohm coax....
>I connected the coax to "Unbalanced" antenna connector on
>the R-390A. It works well.
>
>But as I skim the schematics, it appears that the unbalanced
>antenna connector goes to the secondary side of the input
>preselector(?) CL filters. Does that mean I miss out in the
>first layer of filtering?

Yes.  And the input impedance of the unbalanced antenna connection is such 
that it works better on short antennas such as verticals on a jeep.

>The "Balanced" connection goes to the Primary side the
>"preselector". Would I be better off connecting there?

Yes.

>I know some people connect an unbalanced antenna to the left
>pin of the "balanced" connector and ground the right pin.

Do that and see what happens.

>In the good old days, how would the military connect the
>Balanced connector to a dipole? Would they have some
>sort of 125 ohm dual conductor coax?

Balanced coax.  RG-22 or some such.  It can be had today but is moderately 
expensive.

>Perhaps instead of answering my questions, someone can tell
>me what I need to know...

Feed the radio with the balanced connector.  Ground one side.  Coax center 
conductor to the other side.  Use a lashup or use a real twinax 
connector.  Also, try different TV type balun transformers to see if they 
work better than the one you have.

(There is a "field change" that rearranges the cables on the antenna relay 
so the balanced antenna input coil is both grounded on one side and the 
other side connected to the unbalanced connector.  This is for convenience 
in connecting the antenna if you don't have the correct feedline, or the 
correct adapter for the balanced connector.)

Roy



- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing
13033 Downey Mill Road, Lovettsville, VA 20180
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