[R-390] $71.00 antenna connector

[Roy Morgan]

At 10:37 PM 1/6/2006, pete wokoun, sr. wrote:
>Does this connector tie one of the balanced lines to ground and input the 
>BNC to the other balanced line?


Yes it does. But "WHICH PIN?", is the question.

I recently made some twinax-to-BNC adapters for my R-39x radios. I started 
with a twinax connector from Amphenol (normal cost about $5 ).  I drilled 
and tapped the thread-in cable clamping part to accept a BNC female chassis 
connector, and solved a couple of little problems about wire and keeping 
the twinax pins in place.

While figuring out which pin to ground I discovered MIL- SPECs for the 
UG-970 (twinax male to "UHF" female) and UG-971 (twinax to type C 
female).  According to those mil specs, one of the adapters grounds pin A 
and the other one grounds pin B.  Which is which, I can't remember, but I 
built my adapters to match a UG-970 I have here.

The question remains, does it matter? It may, but I would not expect it 
matters much.  The input circuit of the R-390A has a fixed cap on one side 
and a variable cap on the other side. This allows for setting the balance 
between the two connections of a balanced antenna, done by setting lowest 
received signal for a common-mode input.  It seems to me that the low 
impedance of the antenna system would swamp out any difference brought 
about by grounding out one or the other of the two caps.

Roy



- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
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