Ken Scharf ) writes:
Steve Nosko wrote:
"Michael Black" wrote in message
...

PaoloC ) writes:

Hi.
I have spent part of the weekend trying to resonate al old CB XTAL at
its fundamental frequency.

The XTAL is labelled 27.125 MHz, with a fundamental of about 9.041 MHz,
which falls into 18m HAM band when multiplied by two. I assume 27MHz
XTALs are 3rd overtone....

Could the crystal be a receive crystal? CB crystals tended to show
the channel number or the frequency of the channel, and so if you simply
looked at the marked frequency, it would not tell you if it's for
transmit or receive. Though the ones I've seen did mark them with
"R" or "T". The point is that if it's a receive crystal, it wouldn't
be 1/3 of 27.125 but 27.125-IF and then divided by three.


IFs were frequently 455KHz

But not always! Many cb sets used an if frequency of 1600khz plus or
minus a few 100khz. I have some old Lafayette if cans at 1650khz that
came out of an old cb set. Some also used double conversion with a
first if anywhere from 1.5mhz to 13mhz and a down conversion to 455khz.
So that receive rock could be anywhere in frequency.

Which is why I didn't specify the IF. I thought the original poster
might be listening on 1/3 the marked frequency, but if it's a receive
crystal it wouldn't be there. And while assuming an offset of 455KHz
might be a good 1st guess, one could listen there on a receiver and
still not find something. It still doesn't answer the question of whether
the crystal is oscillating if you don't hear anything at the expected
frequency, because it might be on some other frequency.

Years ago, when I would fiddle with oscillators, I'd put the SP-600 that
I had at the time on it's highest band, 30 to 54MHz. Then with the oscillator
on, I'd spin that knob. A few good spins got it across the dial. I'd find
a spot where there was a carrier, and then do some fine tuning. Then
I'd shift down in frequency, looking for a submultiple of that frequency,
until I found the actual operating frequency.

A digitally tuned receiver let's you find the expected frequency much
faster, but you still need to tune around if the crystal isn't at the
expected frequency.

Michael VE2BVW