[R-390] Balance Caps

[Larry H]

Hi Craig,  Yes this is true if you are using a true balanced input.  If you have a normal single center conductor coax from your antenna, you would need to connect it to an isolation balun that has a 'balanced' output to connect to the 2 center connectors of the twinax connector (not grounding either 1).  This can be very beneficial with some kinds of locally generated noise.

Regards, Larry 


On Sunday, September 21, 2014 4:51 PM, Craig Heaton <hamfish at efn.org> wrote:
 


To All:

For what it is worth, something I printed from Chuck's website years ago.
Hope Chuck doesn't mind.

Balance Caps

Note: It is my opinion that this is an important step which is often
overlooked. You're basically nulling out any signals that are not balanced.
Some noise is of this type. This adjustment can make the receiver quieter in
the presence of common-mode noise.

Connect the signal generator to the junction of two 68 ohm resistors.
Connect the free ends of the resistors to the balanced antenna inputs.
Connect a VTVM to the diode load terminals, adjust the signal generator
output to give about -7 volts diode load volt at the following frequencies.

Frequency
Transformer
Trimmer

00 +000
T201
C201A

01 +000
T202
C205A

03 +000
T203
C209A

07 +000
T204
C213A

15 +000
T205
C217A

31 +000
T206
C221A

Be sure that a true balance is obtained, and not a minimum trimmer
capacitance condition. If you have two dips during the 360 degree rotation,
either dip should be giving a true balance condition. If you only get one
dip over the 360 degree rotation, some component value in the circuit has
drifted too far away from its specified value and the dip is occurring at
minimum capacitance.  
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