The AM Forum

The other day I was sorting a bunch of my crystals and came across some old third mode CB crystals. I thought if they work in the third overtone they should work on the fundamental frequency and if fundamental then they will double and if they double I'm on 17meters. So I set up my Pixie II for 17 meters and they worked.

73 de Gary, KF9CM   

Don't use the Channel 23 crystal - at 18.170 you are out of the band by 2 KC....good luck with the others though.  17 is a great band, even if there are a few too many 24/7 corntest mode DXers who will call CQ DX endlessly with no response, and when you work them, only have the time to give you just the 599 and sometimes not even a 73...then go back to CQing...sort of like meeting someone at a party, saying hello and then immediately walking away from them....rude....And then there's the "rare DX" stations (like a W5/VP5) working split and hardly ever giving their own call signs so you know what all the ruckus is about....

i would have never thunk to use CB crystals this way. A few years back a guy gave me two identical 23 channel CB's. They were junk but I did pull out all the xtals and threw them in a junk box. One of those moments when I thought they may come in handy one day ;D

What made you think of this?

One precaution to consider is that overtone mode is not the same thing as harmonic mode.  In third overtone mode, the crystal is physically vibrating at the third overtone frequency, not at the fundamental, and IIRC, the fundamental may not be exactly one third of the marked frequency of the crystal.  This probably wouldn't make much difference except near band edges.

   

Exactly the reason I don't go out of my way to chase DX on any band. I agree it is rude. Another analogy of rudeness would be to walk up to a group of strangers standing on the sidewalk having a conversation, and butt in without being invited, especially if you then try to change the subject of the conversation. That happens all to often on the ham bands, and probably contributes to much of the "clannish" behaviour that permeates the lower frequency phone bands, particularly 75.

You can probably pull the crystals slightly with a small trimmer cap, xtal controlled commercial radios do that for zeroing to exactly the desired freq.

For working 'split' I would think the 'rx fine tuning' range could be increased somewhat.

Good idea!

Very interesting. I think I have a channel 22 crystal,mabee two of them. That would put me somewhere close to 18.150. Mabee I can get the HT-40 to transmit there. I know my TMC would transmit there.