[R-390] Balanced Vs Unbalanced

[Roger Ruszkowski]

Joe,

You want to use the balanced input.

The common practice is to ground one side and feed the
other side from the center of a coax.

Input impedance varies across the range of the 
receiver but is closer to 600 ohm than 50 ohm.

So a 300 ohm to 75 ohm TV balun can be a help.

If you can find a C connector  for the antenna line,
you can swap the cables between the antenna relay
and the RF deck and use the C connector to feed
the receiver. Then ground the other side by shorting
the twinax antenna connector. In the R390 you have
the option to use a shorted BNC connector in the 
second balanced RF cable.

The reason to use the balanced input is that the 
unbalanced input bypasses the whole first section
of the tuned filters in the RF deck. That stage filters
out a whole lot of out of band signal that then doe snot make it 
into the amplifier and mixers and thus reduces the noise floor
of the receiver 


Roger AI4NI











-----Original Message-----
From: Joe G <jga747 at hotmail.com>
To: r-390 <r-390 at mailman.qth.net>
Sent: Fri, Sep 27, 2013 3:03 pm
Subject: [R-390] Balanced Vs Unbalanced


I have a R390, which antenna lead should I use? Balanced or the Unbalanced. I 
have a 50 ft longwire terminating in a PL-259 connection. Also any way to use 
one antenna on two receivers? 

Sent from my iPhone
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