[ARC5] Crystal work-around question. OT

[Bob kb8tq]

Hi

One ppm at 1 MHz is 1 Hz
One ppm at 10.24 MHz is 10.24 Hz

400 Hz / 10 ( to do it easy in your head) is 40 ppm.

Assuming it is a fundamental crystal. That should be do-able.

Bob

> On Sep 23, 2020, at 3:07 PM, J Mcvey via ARC5 <arc5 at mailman.qth.net> wrote:
> 
> I think it's a bridge too far if i did the calculation correctly:
> 
> The Xtal is 10.240 MHZ
> 
> so (10.24* 10^6/400) * 10^6 = 25600 PPM.
> WOW.
> Guess I'll just have to wait for the part to com in...
> On Wednesday, September 23, 2020, 2:46:13 PM EDT, Tom Lee <tomlee at ee.stanford.edu> wrote:
> 
> 
> What matters is not the absolute frequency shift, but its value normalized to the nominal frequency. Without knowing the latter, it's impossible to say whether 400Hz is a little or a lot.
> 
> Shifting frequency up or down by tens of ppm is easy. Shifting by more than 100ppm puts you into the "difficult" range, while attempting to shift by 1000ppm puts you into the "you might get there, but the crystal isn't really controlling things any longer."
> 
> Adding a series capacitance is easy enough, so give it a shot and see. A practical maximum is a value somewhat below the holder capacitance, but the true limit depends on the topology of the oscillator circuit, among other factors.
> 
> -- Cheers,
> Tom
> -- 
> Prof. Thomas H. Lee
> Allen Ctr., Rm. 205
> 350 Jane Stanford Way
> Stanford University
> Stanford, CA 94305-4070
> http://www-smirc.stanford.edu <http://www-smirc.stanford.edu/>
> On 9/23/2020 11:26, J Mcvey via ARC5 wrote:
> 
> The crystal in question is a sealed HC25U type.
> The frequency is low by about 400 Hz, so it can't be padded. Could it be "brought up" with an adjustable series cap?
> I have a new one on order, but was wondering if anyone had a "fix" without replacing the crystal?
> 
> I suspect too much 'pulling" would cause instability if there was a way.
> What say you guys?
> 
> 
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