[R-390] Mods and Mods

[Roy Morgan]

At 02:20 PM 9/15/2006, you wrote:
>When you do the twinax, which side might matter as the balance trimmer
>affects only one side relative to ground.


Gord and others,

A while ago I equipped myself to make twinax to BNC adapters.  I bought the 
right drill and a tap, to allow screwing the BNC panel mount connector into 
the rear cable nut on the twinax connectors.

At that time I did a web search for the mil specs that define the UG-970 
(twinax to SO-239) and UG-971 (twinax to C).  I seem to remember, that at 
least in the Mil-Specs, the grounded pin of the twinax connector is not the 
same.


HOWEVER,

At Defense Supply Center Columbus,

I find this mil spec for between series adapters:
<http://www.dscc.dla.mil/Downloads/MilSpec/Docs/MIL-DTL-27434/dtl27434.pdf>
and in there, a table tell of Signal Corps drawings:

UG-970  SC-106729
UG-971  SC-106728, neither of which I can locate

And I find the following two Mil Specs for the UG-970 and UG-971:

UG-970   MIL-A-27434/23A  mil27434ss23.pdf
<http://www.dscc.dla.mil/Downloads/MilSpec/Docs/MIL-DTL-27434/mil27434ss23.pdf>

UG-971   MIL-A-27434/24A  mil27434ss24.pdf
<http://www.dscc.dla.mil/Downloads/MilSpec/Docs/MIL-DTL-27434/mil27434ss24.pdf>

A close look at these shows that, with the adapter's male pins facing you, 
and the right angle female part pointed down, the male pins are oriented in 
a vertical plane: that is, parallel with the female part, and importantly, 
the key that engages the slot in the chassis mount connector is at the right.

Both the UG-970  and UG-971 have the lower pin grounded.  That is the pin:
  - clockwise from the key slot in the adapter as viewed from the end of 
the male pins.
  - counterclockwise from the key in the chassis mount female connector as 
viewed from the outside.

>I followed the balance method with two resistors aiming for a null as in 
>the book but single sided input might be better adjusted. Any thoughts?

If you ground the side that has the balance trimmer, it won't do much if 
anything. If you ground the the other side, it may also not do much. The 
balance trimmer is adjusted for minimum signal with BOTH sides of the 
connector fed the SAME signal.  The other trimmer in the can is adjusted 
for strongest signal: it tunes the secondary of the coil and should be 
adjusted with one side of the input coil grounded (or fed a signal between 
both ungrounded pins.)


Roy




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