From: WarmSpgs@aol.com
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Date: Tue, 13 Aug 2002 15:38:59 EDT
Subject: Re: LF: Oscillator Stabilty for QRSS?
To: rsgb_lf_group@blacksheep.org
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In a message dated 8/13/02 2:54:19 PM Eastern Daylight Time, 
jsm@gulfislands.com writes:

<< I am worried about drift but also thinking that they may be stable enough 
if kept in the 1 - 2MHz region. As well, they should (if identical) drift by 
the same amount and thus be self-correcting? Is this a reasonable avenue to 
pursue or should I just break down and buy a couple of xtals?? >>

I'd go for the crystals, Steve.  The stability of even relatively inexpensive 
crystals in the HF range is much better than you can expect from VFOs.

Your oscillators will drift by the same percentage amount, not the same 
absolute frequency amount.  Remember those halcyon days of algebra class, and 
working with the good old associative property?  Lets imagine two 2MHz 
oscillators each maintaining a rather good 50ppm over the temperature range 
of the room in which they are kept, and if they do track comparably, f1 will 
have a potential drift of 50ppm of 2MHz and f2 will have a potential drift of 
50ppm of 2.136MHz (that is, a few more Hertz of drift than the f1 
oscillator)--which, when one takes the difference of f1 and f2, is the same 
error as 50ppm of (f2-f1).  Thus, the output has the same percentage 
tolerance as the original oscillators.
     Unless they were unusually well stabilized, VFOs would not be good for 
more than the shortest QRSS dot times, and probably not at all suited for a 
JASON transmitter.

73,
John