[R-390] (no subject)

[Roy Morgan]

At 03:31 PM 3/23/2007, n4buq at knology.net wrote:
>Gang,
>
>Is there a right and a wrong way to feed the balanced input with unbalanced
>coax?  I found two different versions and wonder if it makes any difference
>which way it's done.
>
>http://www.qsl.net/k5bcq/r390/r390.html
>
>http://www.r390a.com/html/feedpoint.html

Barry:

Those two methods wind up with the same result.  Here are some comments:

It may matter which pin you ground.  Here's why:

MIL-A-27434/24, 28 September 1960 describes the UG-971, twinax to type C 
adapter.  This  MIL-Spec show the index slot in the inner shell of the 
connector as being to the LEFT as you view the pins of the twinax connector 
and the other end of the connector downwards.

MIL-A-27434/23, 28 September 1960 describes the UG-971, twinax to "UHF" (or 
SO-239) adapter.  This Mil Spec shows  the index slot in the inner shell of 
the connector as being to the RIGHT as you view the pins of the twinax 
connector and the other end of the connector downwards.

HOWEVER, I have a photo showing one each of these adapters and both of them 
have the slot to the RIGHT as you view the pins of the twinax connector and 
the other end of the connector downwards

What this means is that depending on which of these two adapters you have, 
OR which way your particular adapter is made, you will be grounding one or 
the other of the twinax terminals and the other goes to the center of your 
coax.

Whether this matters, I do not know!  It could be that the adjustment of 
the Antenna Input Balance capacitor on the RF input transformer would make 
a difference. It could be that if the thing is adjusted per the book (RF 
fed equally to both pins and adjust for a null in received signal) that it 
won't matter which one you ground.

  I suggest you try it both ways and let us know. An  easy way to change it 
once you have your coax lashed up to the twinax connector, no matter how 
you do it, is to reverse the two coax wires to the RF deck from the antenna 
relay  which carry the balanced RF.

Roy


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