[Hallicrafters] SX-71 2nd Oscillator Stability

[Edward B Richards]

Hi Bob;

It doesn't seem reasonable for such a low frequency oscillator to drift
so much. I was a little surprised to see it is free running instead of a
crystal. I suggest you replace all the caps with the correct temperature
compensation. If it were me, I would make it a crystal osc. It looks
easy. If you really want stability, put the crystal in an oven. I have
some if you want one. Good for 5 PPM. Good luck.

73, Ed Richards K6UUZ


On Fri, 21 Jan 2005 11:42:35 -0800 "RJB" <rjb at lynden.com> writes:
> Good morning to all Hallicraftees...
> 
> after several months of boatanchor absence i am back to working on 
> my SX-71.
> A few months back i installed an AADE digital readout (DFD) unit on 
> this rx.
> This unit works great; it is easy to calibrate, and reads dead right 
> :-)
> 
> for one minute :-(
> 
> The DFD is driven from the first oscillator, ie the variable one. 
> This is
> reasonably stable, which means that the DFD readout stays reasonably 
> steady
> over, say a 30-minute period. However in this period the radio 
> itself may
> have drifted 2-3 kHz. Reason appears to be that the 2nd osc has a 
> slow but
> persistent drift.
> 
> Yeah i know - serves me right for installing digitial readout on a 
> radio
> that wasnt designed for it... Hey, before you laugh *too* loud, i 
> have used
> DFD's for years on my Hammarlunds with excellent results.
> 
> So... anyone else encountered stability problems with the SX-71 2nd 
> osc??
> Any remedies??
> 
> FWIW i have replaced all resistors and all bypass caps on this rx 
> (maybe
> this is the problem).
> 
> thanks in advance for any help
> 
> Bob Bennett, Maple Vly, WA
> 
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