09-02-2013, 08:42 PM
Now that you have the detector aligned, you can proceed to check the IF bandpass response. If you have a dual trace scope, you can leave one probe on the FM detector output and place the second probe on the AGC output of the diode detector (7C6) . That way you can see the IF response superimposed on the detector curve. They should line up so that the IF response is in the center of the linear portion of the detector slope. If the IF response is flat topped with steep sides and centered on the detector reponse, then you are all done!
You will need to connect a 47K resistor in series with the scope probe when connecting to the diode detector ( junction of R417 and R412), to prevent loading of the RF signal present there.
You will need to connect a 47K resistor in series with the scope probe when connecting to the diode detector ( junction of R417 and R412), to prevent loading of the RF signal present there.