kevzep
Its all about the Music
The IF sweeper method to adj detector linearity has its flaws. Look at later model procedures and they use this method.
Most ratio detectors and quadrature detectors use the same method, DC zero with no IF i/p (only noise) and then adjust for linearity with full mono 75KHz modulation at a reasonable level to get the recovered audio at its S/N limits, say >100uV-1mV.
The best method is with a THD or spectrum analyzer, as your eye can not see this fine differences in linearity, eye/sweeper is a coarse adjustment method.
Methods using IF sweepers/markers wereused for aligning tuned IF stages (L/C) since it was easy to see the filter responses and symmetry.
Sweeping a RF front end is an excellent way to adjust the RF tuned stages since they are usually L/C ckts. Not too many people have RF spectrum analyzers and tracking generators, I for one,
Thanks Rick, really appreciate your responses here, I'm learning a bit from this...I'm going to try this method for the discriminator, I appreciate the angle you are coming from with regards to the visual...
I guess the manufacturers assumed in the service shops, the tuners would be pretty close to start with, so quick check and if anything was "out of whack" it would be fairly obvious..
I need a Spec analyzer as I work for an audio hire company, and we have a large amount of RF microphones and wireless personal monitoring, its good to use the spec to compile a large system with them all working together, in the same rack, we can have upwards of 16 RF mics and around 10-12 personal monitoring systems, if you are not careful with assigning you frequencies, all hell can break loose as you can imagine....
I digress though....
I'll report back, as I have a tuner here I need to look at in a Sansui QRX7500A, I think its out of whack, so I will try this method.
I hope you don't mind me jumping in here John, we can all learn a bit more this way?
I agree with what Rick has said, try that method, you'll get your tuning meter lined up which will in turn bring you a better alignment, when the discriminator is off, FM stereo can be quite distorted etc etc...