Quote:
Originally Posted by simpsons
You don't need to use a FM signal generator, a FM broadcast will be fine for AM rejection adjustment on the discriminator; using the DC motor or other man made interference to tweak it.
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It would take a pretty brave person to suggest a company like Philips went to all the trouble and spent all the R&D money, hired many well educated & professional RF engineers to build an FM capable sweep generator with a very accurate high resolution digital frequency display (based on an Intersil IC and crystal timebase) and accurate markers, because it wasn't a requirement to properly align an FM radio with a discriminator or a ratio detector. And that it could have been done satisfactorily with a "listening test". Does that sound right ?
It is not just about AM rejection, it is about ensuring a symmetrical linear translation function of +/- frequency offset with the detector output over a range that corresponds to the max frequency deviation. So it requires the sweep, with markers, to be sure it is correct. Especially in the case, that the fundamental fault is that it appears that the output from the detector, in the OP's radio, is distorted in some way.