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Old 16th May 2021, 7:13 pm   #1
Superscope
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Default 20.431 Mhz Crystal wanted

Hi forum,

Now this is probably a long shot, but I'm looking for a
20.431 Mhz Quartz Crystal for a PLL circuit.

Does anybody know where I might find one?

I can find 20 Mhz Crystals, no problem, but I won't be able to
pull those up to the required Frequency.



Ian
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Old 16th May 2021, 7:35 pm   #2
G6Tanuki
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Default Re: 20.431 Mhz Crystal wanted

In the last year I've had the guys at QuartSlab - http://www.quartslab.com/ - cut some crystals for me - these were 5.mumble MHz ones to put my AEl3030 transceiver on 3.6/3.7MHz but they offer a good service - the crystals mthey did for me came up mwithin 100Hz of the target frequency and have not gone-a-wandering frequency-wise over the last half-year [drifty crystals were a bit of a probllem with some suppliers in the 70s and 80s - a 250Hz drift when multiplied x32 or x36 in a VHF/UHF transmitter could put you on the next-channel-up!]
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Old 16th May 2021, 9:44 pm   #3
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Default Re: 20.431 Mhz Crystal wanted

When you go to talk to a crystal manufacturer, one of two things will happen:

1) They will ask you what function it has and in which radio. Then, if you're lucky, they will have done crystals for this job (maybe different channels) before and know the recipe.

2) If they haven't, or it's something new they will need some data:

Case?
Series or parallel mode?
Load capacitance, pF?
Fundamental, or what overtone number?
Max temperature drift and over what temperature range.
Adjustment tolerance?

20.431MHz could be a fundamental or 3rd overtone. Pullability diminishes as the SQUARE of the overtone number, so a 3rd overtone crystal is 1/9 as pullable as a fundamental one. Series mode oscillators are somewhat more common. 10ppm adjustment and +/-10ppm over 0-70C would be a high quality crystal. 100ppm is microprocessor clock territory. To allow adjustment either way, spec'ing a 30pF or 20pF nominal series C is pretty usual.

David
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Old 17th May 2021, 10:54 am   #4
G6ONEDave
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Default Re: 20.431 Mhz Crystal wanted

Sorry I don't have the exact crystal but here is a list of 20Mhz range that I do have incase anything might be pullable for your application.

20.030, 20.105, 20.250, 20.550, 20.7360 and 20.930Mhz. No idea what the capacitance is for any of these or if series or parallel loading.

David is right about the questions for getting new crystals cut. I tried to get some last year but not knowing all those specifications failed, I even sent a copy of the circuit for their tech guy to try and work it out. I never got any response, so decided to use the vco method for my application.

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Old 17th May 2021, 12:07 pm   #5
Restoration73
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Default Re: 20.431 Mhz Crystal wanted

20.330 is a popular CB loop mix frequency, I have that and also 20.482 if these are any
use to you ?
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Old 17th May 2021, 12:34 pm   #6
SiriusHardware
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Default Re: 20.431 Mhz Crystal wanted

Supercope, if you contact the likes of Quartslab (Post #2) and tell them the PTBM... (or whatever) board number in that radio and that it's a band crystal they will probably know the rest of the needed detail, or if you were willing to send them one of the existing loop mixer crystals to analyse, they can do that (you would get the original crystal back along with the new crystal as long as you made clear that you wanted to retain the original).

Bear in mind that just changing the loop mixer crystal won't rearrange the channel frequency steps, you'll probably have to use an EPROM to do that.
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Old 17th May 2021, 2:12 pm   #7
Ian - G4JQT
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Default Re: 20.431 Mhz Crystal wanted

Try this guy if he's still around. He has access to all sorts of unused crystals:

voyjako@gmail.com or vincentvoy@hotmail.co.uk

Vincent Jakomin IQ Electronic design. Had a quick google, but not sure he's still around, anyway see what you can dig up - let us know if he's still available.
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Old 17th May 2021, 2:14 pm   #8
Superscope
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Default Re: 20.431 Mhz Crystal wanted

Thanks for the replies everybody.
Much appreciated and all very helpful.

It is certainly my intention to contact Quartslab
if I can't find a suitable Crystal knocking around,
so thanks to G6Tanuki for the Link to them.




Ian
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