[R-390] RF Deck Alignment Question

[Bob Camp]

Hi

If you drive the radio through a transformer they are very useful for  
rejecting common mode noise. In a "one side grounded" drive they  
don't do much good.

Bob


On Jun 9, 2007, at 2:09 PM, Craig C. Heaton wrote:

> 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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