[R-390] Crystal substitution puzzle

David Wise David_Wise at Phoenix.com
Fri May 15 13:36:44 EDT 2009


http://www.phy.auckland.ac.nz/Staff/geb/Crystal%20Oscillator.pdf

There are many others.  I used

	microprocessor "crystal oscillator" colpitts pierce

as my search string.

When I said "operated inductively", I was referring to
parallel-resonant mode, where the crystal's equivalent
impedance is inductive, as opposed to series-resonant
mode where the crystal looks resistive.  The Colpitts
oscillator (used in the R-390A) utilizes the inductive
aspect of the crystal.  (Actually, the crystal is
not operated right _at_ its antiresonance point, but
somewhere between antiresonance and series resonance.)

Dave

-----Original Message-----
From: Roy Morgan [mailto:k1lky at earthlink.net] 
Sent: Friday, May 15, 2009 9:56 AM
To: David Wise
Cc: r-390 at mailman.qth.net
Subject: Re: [R-390] Crystal substitution puzzle


On May 15, 2009, at 12:25 PM, David Wise wrote:
...  Out on the net there's an analysis
> of series- vs parallel-mode crystal operation

Can you post the URL?  Thanks.

> ... a series-rated
> crystal operated inductively will run above rating,
> not below.

I assume that you mean above rated frequency, and inductance in  
series.  It could well be that inductance in series has the opposite  
effect as capacitance in parallel.  The R-390 circuit, we can assume,  
has more capacitance in parallel with the crystal than the new  
crystals are meant to have.

(No, I have not puzzled this out by analyzing the equivalent circuit  
of the crystal and all that.)

Roy

Roy Morgan
k1lky at earthlink.net
529 Cobb St.
Groton NY, 13073
Home: 607-898-3607
Cell: 301-928-7794





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