Re: Tek 494AP VR board mystery


Ed Breya
 

I don't know the circuit here, but you may want to look at the logic and PIN control circuits and circuit descriptions in more detail. Sometimes a couple extra dB attenuation or passing, depending on the situation, makes things work much better. It may boil down to turning on a PIN harder, to short signals to ground, or to get a little more through signal, in certain spots. Also note that in many setups, the Q (hence BW) of the crystal RBW IF filters is set by variable PIN RF resistance (DC control current), so that aspect has to be handled in the overall biasing scheme.

Ed

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