[R-390] RF Deck Alignment Question

[Craig C. Heaton]

Hi Bill,

The following is something I ran across and have used on a R-390/A. YMMV.  I
believe the bal caps are for the rare occasion you truly have a 125 ohm
balanced antenna connected to the receiver.

73's
wd8kdg
Craig,

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 voltage, and minimize this voltage
at he 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 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.



Hi Everyone

I'm in the process of doing the RF deck alignment.......what are the cap
trimmers
marked (BAL)?? on the slug assembly. Perhaps not used?

Thanks for reading

73

Bill  KB9IV
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