[TenTec] Corsair 2 not stable on receive, 20 meters

[Lee WA3FIY]

Dwight,
On 20 meters and a few other bands the PTO (Corsair II) is shifted slightly by a small DC 
bias applied through SW4 and a resistor/pot combination on the OSCILLATOR MIXER 
BOARD.  Perhaps the switch contacts for 20 meters are dirty causing intermittent small bias 
changes, hence frequency change.

Also note that only on 20 meter the PTO bypasses the crystal mix circuit.  Although unlikely, 
there is a chance that the PTO is being loaded by following circuitry causing frequency 
shifting.

I've not had good luck with huff-n-puff type frequency correction circuits on phase sensitive 
digital modes.  First, the frequency must move before a correction can be made.  That shift 
causes decode errors.  Secondly, the frequency correction itself causes  errors.  The circuits 
I've tried have all been home brew.  Maybe some of the commercial circuits have eliminated 
those problems. 

73,

-Lee-


On 19 Jan 2015 at 15:43, Dwight Orten wrote:

> My I been working PSK with my old Corsair and I am starting to have
> trouble on 20 meters.  Watching the waterfall, the incoming signal
> drifts off and my software can,t decode it.  Sometimes it comes back,
> sometimes I have to chase the signal.  I don't know if it is doing the
> same on transmit.  The frequency readout is not showing any change
> when this happens.  On all other bands the waterfall lines are
> straight as an arrow and no trouble coping.  The PTO has never been
> rebuilt, but it seems to me if that was the problem it would be on all
> bands. Any thoughts, anyone? KM4FO Dwight
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