17-04-2012, 08:49 PM
Putting the 'scope across the volume control is a way of connecting the 'scope to the output of the A.M. detector. That way, as the generator sweeps through the I.F. passband, the resultant R.F. output from the I.F. amp. is rectified by the detector and a d.c. voltage is thus produced. The resultant display on the 'scope is thus a curved line - this being the graph of the response of the I.F. amp.
If the 'scope was connected to the O/P of the I.F. amp., prior to the detector, (which is another way of using such a test set-up) what you would see on the 'scope would be two 'humpy' curves (a mirror image, one above the other) with the region between those curves being a 'blur of R.F.' What the detector is doing is chopping off one of those curves and its filter is removing that blur of R.F. - thus leaving just the curved line - the d.c. O/P from the detector.
Al.
If the 'scope was connected to the O/P of the I.F. amp., prior to the detector, (which is another way of using such a test set-up) what you would see on the 'scope would be two 'humpy' curves (a mirror image, one above the other) with the region between those curves being a 'blur of R.F.' What the detector is doing is chopping off one of those curves and its filter is removing that blur of R.F. - thus leaving just the curved line - the d.c. O/P from the detector.
Al.
