[R-390] Antenna Connectors

[Barry]

Along the lines of antenna connections, I "discovered" something interesting
the other evening.  For testing purposes, I have been connecting my RG-58 to
the unbalanced input.  I decided to switch to the balanced input.  When I
connect the center conductor, the radio jumps to life; however, when I
connect the outer shield to the other pin (not grounding either pin), the
received signal becomes much quieter and about a 10dB increase in signal
strength (according to the Carrier Level meter).

I figure this is because I aligned it to the balanced input (with a
lower-than-125-ohm impedance), but I was kind of surprised at the difference
I could detect between the two inputs, especially when I disconnected one
pin on the input (the coax's shield).

One other thing: the antenna input caps (the ones in the first transformers
that go across the first transformers) don't do ANYTHING.  Is this simply
due to too much impedance mismatch?

Barry - N4BUQ

----- Original Message ----- 
From: "Bill Abate" <wabate at verizon.net>
To: "Barry" <n4buq at aol.com>
Cc: "R-390 HF Receiver List" <r-390 at mailman.qth.net>
Sent: Friday, January 13, 2006 11:23 AM
Subject: Re: [R-390] Antenna Connectors


> Barry,
>
> I replaced the 'unbalanced' connector with an SO-239 but I did it
> differently.  The original connector was bashed in, so I did not have
> anything to loose.  The connector is merely soldered in.  I removed it
> (forcefully) and cleaned up the residual solder in the socket of the
> relay housing.  I then removed the flange of the 239 and trimmed it
> slightly on a lathe so that it would fit the existing opening.  Then I
> soldered the SO-239 to the relay housing.  Then you just have to
> reconnect the center connector.  Not hard but you need a lot of heat for
> solder to flow on that massive housing.  Everything else stays the
> same.  In effect I eliminated an adapter.  Then I grounded one pin of
> the twinax connector.  I think I swapped the mini bnc's as is documented
> elsewhere to connect the antenna to the RF coils.
>
> 73,
>
> Bill, K3PGB
>
> Barry wrote:
>
> >Not intended to be a "Mish" post, but was interested in the mod I see on
the
> >radio displayed on the "Strip Alignment" page:
> >
> >http://www.dxing.com/r390/strip.htm
> >
> >Anyone else decided to remove the antenna relay and replace it with a
> >SO-239?
> >
> >Barry - N4BUQ
> >
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