How to add offset dc adjustment to a circuit (YIG filter driver)

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hafrse

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Hello,

I have an old spectrum analyzer with outdated calibration, and need to fine adjust the offset voltage (with a multiturn pot ) of the preselector YIG filter, attached is the circuit diagram.

PSDR+ (Preselector control voltage)
PSDR- is ground from the controller
+MTXV is the supply voltage to the YTF (+26V)

The fine adjustment offset should be around U10 I think, any suggestions how to add that on this circuit?

Many thanks!

George
 

chuckey said:
R36, 1K? or is it mean't to do something else?
Frank
Click to expand...

Hello,

I tried there, it did not change any thing, obviosly it does something else
Thanks

- - - Updated - - -

Hello,

More information:

The analyzer can however adjust the offset through a menu entry but after shutting down the analyzer, the values are read from the calibration data which are outdated. I need to do this procedure every time I power the analyzer ...

I measured now the needed offset at TP-10 (the PSDR+ signal from the AD converter) , the offset range of +/- 250 mV is enough.
So now, how to add an offset at TP-10 of +/- 250 mV with a multiturn pot?
Many thanks!
George

- - - Updated - - -

Attached is the schemtics for the source of the PSDR+ signal (TP-10), output signal is the right from Q13 and Q14
 

How about measuring the DC around the circuit as it is. Then actuate the menu driven off set control and alter the offset a lot then measure the DCs again. This will give you a clue as to what the off set actually does, could put a saw tooth on a pedestal some where else for instance.
Frank
 

Thanks for the information, I actually did, when I rotate the offset soft konb, the offset dc goes up and down about 200 mV . I also measured what offset I need to get the YIG filter linear in almost all frequncies, it is around +40mV , so the needed offset is a very stable positive dc of around 40mV .
George
 

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