Thread: AD603 IF Amp.
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Old 20th Nov 2022, 4:32 pm   #1
Wendymott
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Default AD603 IF Amp.

Hi peeps. Complicated circuit analysys is not my strongest point, and I usually put faith into the manufacturers application data, assuming they know what they are doing.
See attached circuit. It is billed as an AGC amplifier ... which was duly laid out on a pcb and tested. Unfortunately iit has no AGC function. The AGC line stubbornly sits at 5 v whatever the RF input. It makes a good attenuator.

The output only rises with large amounts of RF in. There is no sign of the 84 db gain it is supposed to give. In desperation I disconnected the AGC line and fitted a 10K pot from + to Gnd. and then I can get gain, but not the 84 db promised. Has A D put in one of their "errors", that I am not clever enough to work out ?
No doubt Jeremy and David will be rolling their eyes upward, but no matter
Your comments would be gratefully received.
Oh yes incidentally some of the very accurate resistors in the original circuit had to be trimmed, as R12 = 820R and the pin 4 bias has 2K7 resistors.
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Wendy G8BZY
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