[R-390] Antenna Input Modifications

[Drew Papanek]

K3PID wrote:

>On my R-390 someone removed the twinaxial socket on the balanced input and
>replaced it with an SO-239. The center conductor of the new connector 
>passes
>thru to the high side of the transformer while the other side is now
>grounded. Was this a common mod? why wouldn't you just replace the 
>connector
>on the unbalanced input with the SO-239?

The unbalanced antenna input is connected to the grid side of the RF input 
transformer and hence is high impedance. That was intended for use with a 
short whip antenna.

The balanced input is low impedance but many of us do not use balanced 
feedline.  Grounding one side lets one use the other side as an unbalanced 
low impedance input.  There was a Navy "modification" which consisted of 
juggling the 3 internal BNC's (or MBNC's) to use the unbalanced input 
connector as low impedance in the aforementioned fashion.

Drew

"Vicariously repairing and modifying R-390x via advice to others"

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