[ARC5] Crystal work-around question. OT

[Tom Lee]

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

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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