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Old 12th Oct 2017, 1:40 pm   #12
Argus25
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Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
Default Re: 'I.F Alignment Aid'

Back on the topic of IF alignment.

I have found over the years that, in the case of AM radios , its seldom necessary to do a sweep of the IF. The reason being that in many cases (for transistor sets) the IF's are single tuned and for double tuned ones they are intended to be set (peaked) to the same frequency. The band pass characteristics are set by the design of the IF transformers by the manufacturer. So they are simply peaked. Its not necessary to see the shape of the response.

It is totally different for TV IF's where they cannot be set up very well without a sweep. Many manufacturer instructions for peaking at specific frequencies turn out to be pretty hopeless when you check with a sweep after you have done it.

The one exception though, is the FM detector in a radio, be it a discriminator or ratio detector. To get its symmetry correct and center frequency right, a sweep is really needed.

But for any standard AM radio, an IF sweep in my view has very limited utility (unless you are making home made IF transformers)... just to throw a cat into the pigeons here.
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