[TenTec] Corsair II DDS VFO

Carl Moreschi n4py2 at earthlink.net
Tue Mar 22 09:21:58 PDT 2011

The counter in the Corsair counts the sum frequency of the PTO and band 
crystal.  The IF frequency of 9 mhz is put into the counter as a 
starting point.  So if the counter oscillator is right on the mark, the 
displayed frequency has to be exactly right.

If you tune in WWV in USB or LSB and get it zero beat, you can then 
adjust the frequency counter trimmer so the display shows exactly 
10.000.0 and you should be exactly correct on all bands.

This is a different scheme than used in the Omni V and Omni VI and is 
really quite good for SSB because it takes into account the band crystal 
error.  For CW, the displayed frequency is off 700 hertz because of the 
CW offset.  Even this could be corrected by starting the counter at 
89993 or 90007 depending on UCW or LCW.  I used to have an Omni A series 
B that I added the Tentec external display to.  I added a switch for CW 
mode that changed the counter's initial value.  This made the displayed 
frequency even in CW right on.

Carl Moreschi N4PY
121 Little Bell Dr.
Hays, NC 28635

On 3/22/2011 12:02 PM, Dr. Gerald N. Johnson wrote:
> If the DDS setting was independent of the readout in the radio it
> wouldn't take into account differences between the crystals where some
> bands are offset from even MHz to cut down on receive birdies. That
> means accuracy is dependent on the accuracy of the offset programming
> and the display counter clock yet.
> 73, Jerry, K0CQ
> On 3/22/2011 2:50 AM, Steve Hunt wrote:
>> Greg,
>> The DDS modification still uses the Corsair's "native" frequency readout
>> circuitry, so setting accuracy is no better or worse than with the PTO.
>> 73,
>> Steve G3TXQ
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