Talk:Radio Crystal Identification
identifying scanner crystals
If you have a crystal scanner available, even if the frequencies in question are not in use in your area, you can at least determine which type of scanner they are for, using the local oscillator. Plug in a crystal (VHF high-band), then look for a signal 10.7 or 10.8 below the marked frequency. For 154.430, listen on or around 143.73 (-10.7) and 143.63 (-10.8) with a second scanner.
I'm not too sure about the lowband crystals. They are probably fundamental, high-side injection. For 46.12, you'd check 56.82 (+10.7) and 56.92 (+10.8) if you have a receiver to cover that range.
references
decipher these
I'm hoping that it's a 48Mhz crystal. Or, is it bad news and I've got a 98Mhz rock?
You never know how a crystal will be marked. Sometimes with the overtone frequency, more often with the final multiplied frequency, or, if designed for a receiver, the receive frequency (which is offset from the crystal frequency by the IF, either up or down.)
I have an untuned crystal oscillator that drives an LED (which indicates that the crystal is actually oscillating) and I hook up my frequency counter to find where it is oscillating.
A 48 MHz overtone crystal will oscillate on the fundamental, which should be around 16 MHz. (To get it to oscillate on the overtone frequency, it needs to be used in a circuit that provides suitable feedback only at that frequency.)
The upper limit for crystals is about 20 MHz or so (occasionally to 25 MHz.) Above that the quartz is too fragile, etc. So for the higher frequencies a lower frequency crystal is run in overtone mode - the actually overtone frequency is a little higher than what you would get by multiplying up the fundamental.
If you want to pull the crystal to get it on your favorite 2m channel, it will be easier if you run it on the fundamental than in overtone mode: a 16 MHz VXO followed by a tripler will give far more pull range than a 48 MHz overtone oscillator.
