FM TUNE UP

  
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At some point every ham working with FM radios has need to do some tuning of the transmitter and receiver. If you are like me and lucky enough to have professional test equipment, this task is easy. If you don`t have access to professional equipment, you just have to be a little more clever. Note that a good deal of what I have to say here applies
FM TUNE UP - schematic

equally to the popular Mitrk and Maxar Motorola radios along with most other crystal controlled amateur and commercial radios. The basic principles are the same. If you become confused by what I have to say about local oscillators, mixing and "IF strips, " I strongly recommend reading about those subjects in the ARRL handbook. The knowledge you will gain you will find extremely valuable in the future. Setting the frequency of both the transmitter and receiver in a crystal controlled radio is pretty straight forward. Frequency counters that work on the 2 meter and 70 cm bands are common place and affordable. A decent counter in calibration gives you a good test equipment foundation that is hard to beat for the cost. With a counter transmitter frequency alignment is pretty simple and straight forward. First off allow all of your equipment (this includes the radio to be serviced) time to warm up so all of the oscillators are stabilized. I would wait at least 20 to 30 minutes. Make sure that YOUR test equipment is in calibration! It sure does not hurt to run a calibration check of your own gear before working on something as sensitive as a 9600 baud data radio or a repeater. If you are using a ham type counter keep in mind that most inexpensive counters do not have crystal oven. This means that it is very easy for your counter to be off frequency and lead you astray. If you are lucky, your counter will use a time base crystal...



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