[R-390] antennas

[Bob Camp]

Hi

You can go *very* crazy trying to match a random wire antenna.  
Guessing it's impedance is tough because of all the variables. Best  
bet is to try a couple of ideas and go with what worked best. You  
probably will find that what works best at some frequencies works  
poorly at other frequencies.

The best way to feed a 390A is with balanced coax. That's only true  
if you feed the coax from a balanced source. Since you want high  
impedance, you need both a "choke" balun and a matching transformer.  
I have had pretty good luck with doubled small diameter coax wound on  
2" EMI cores for the chokes. Yellow or red iron cores work okl for  
the matching transformer if you get up above 1 1/2" diameter. Stick  
with teflon insulated wire / twisted for the windings of the  
transformer section.

Bob
KB8TQ

On Oct 17, 2007, at 9:31 AM, Rasputin Novgorod wrote:

> Hi Guys:
>
> My random wire connects via a 9:1 un-balun to 50 ohm coax.
> The shield is grounded. Because I had the correct adaptor,
> 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?
>
> The "Balanced" connection goes to the Primary side the
> "preselector". Would I be better off connecting there?
> I know some people connect an unbalanced antenna to the left
> pin of the "balanced" connector and ground the right pin.
>
> 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? Surely not
> ladderline.
>
> Perhaps instead of answering my questions, someone can tell
> me what I need to know...
>
> Sincerely,
> /blair
>
>
>
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