Test-eq-free FM Tuner Alilgnment

I remember many years ago building a Knight-Kit AM-FM tuner from a kit. When it was finished there were instructions for aligning it, using no test equipment. Just the built in signal strength meter. I would like to try this on a couple of FM tuners, but can't remember the procedure. As I remember, the results were quite good. Anybody know how to do this? Seems like a working fm tuner was placed next to it, for a "bleed-over" oscillator signal.

Using the local oscillator signal from an AM or FM radio as appropriate is an old trick. But it is mostly only useful for the RF front end. To do a proper alignment you need an IF signal and a multiplex signal at the very least. And for the best results you need an RF sweep generator and an oscilloscope.

Back in my youth on the farm, not having a lot of funds or access to test equipment, I made a "test set" from an AM/FM radio. Installed BNC connectors for the output of the tuned RF stages, both local oscillators, both IFs and and audio out. When I "moved up" to stereo I also used the 19kHz oscillator and and buffered the various outputs. I was tall corn. That is an old farm saying.

I did the same thing with a multi-band shortwave receiver so I could trouble shoot my ham radio gear.

Is it the best way, not by a long shot. Did I find it handy, you bet I did.

To do a proper alignment you need the proper test equipment. For FM stereo an FM stereo signal generator is recommend.

You post has reminded me of another thing that I did. I wanted an FM transmitter. Again faced with a lack of funds I used a radio. Added a variactor diode to the local oscillator and fed it with and audio signal. Put a piece of wire on the output of the local oscillator and wow I had a FM transmitter. Then I moved on up and added a pre-emphasis circuit to the audio path. Boy, was I ever plowing corn down the center of the row. Next step was to pull an RF transistor from another radio and add an RF output buffer amplifier to my "broadcast quality" transmitter. I was happier than a hot pig in a cold mud hole.

It appears that the RF front end is where my problem lies. The signal strength meter shows a weak signal, and it is right after the RF section. Working on a Pioneer SX-850. The strongest stn in the area comes thru with a strong enough signal to produce a usable signal, but it is the only one. The same antenna used on other receivers produces satisfactory results.

First try cleaning the tuner. See the sticky in the Tuners section.

Unless someone has been dinking around with the receiver I would tend to think the problem might be with component(s) that have changed value over time (or as the good Dr. said, need cleaning). So, my question would be, do you really want to change the alignment of a good receiver based on possible bad parts?

JBL GUY said:

I wanted an FM transmitter. Again faced with a lack of funds I used a radio. Added a variactor diode to the local oscillator and fed it with and audio signal. Put a piece of wire on the output of the local oscillator and wow I had a FM transmitter.

Click to expand...

I remember doing that, too, about 30 years ago! But, just by accident as I didn't know much about radios. I couldn't seem to find the right spot to put any antenna, however. But even so, the receiver still broadcast through a few walls and, maybe, a hundred feet away!

FM RF alignment can be done without a generator. Basically, you tune to a station at the high end of the band, adjust the RF section trimmer capacitor(s) for maximum signal strength, then tune to a station at the low end and tweak the RF section coils. Repeat until there's no further improvement. Do NOT attempt if you cannot positively identify the relevant tweaks. You may need specialty diddle sticks, most likely for the coil cores.

Thanks, Mike.

Sounds like what I'm remembering from the old Knight Kit project. I'll give it a try