Foundations Of Amateur Radio

Foundations of Amateur Radio The frequency you listen and transmit on in a modern radio is derived from a crystal master oscillator, in my case 22.625 MHz. That master frequency is multiplied and divided to determine the final frequency. To get to 2m you need to multiply by 6. To get to 70cm, multiply by 20. Similarly, to get to 40m, divide by 3. Any slight variation of crystal frequency has an impact. 100 Hz variation in the master oscillator causes the radio to be off by 600 Hz in 2m, or 2000 Hz in 70cm. The higher you go the bigger the error. This leaves us with two problems. If the crystal changes frequency over time, your radio wanders with that change which is especially noticeable on the higher frequencies. I've previously discussed how you can deal with the variation by correcting for temperature. The other problem is the actual absolute frequency. If the radio is set-up for a crystal with one frequency and you replace the crystal with a different one, how do you know what frequency you're actuall