[R-390] Collins R 389 PTO

[Mark Huss]

There are several DDS (Direct Digital Synth) VCO kits running around, 
mostly based on the AD9850 or AD9851, for a hundred dollars or so.  With 
a range of 0-40+ MHz, it would be ideal.  The issue is the encoding.  
The PTO  covers 1.06 MHz in 10.6 turns, or 100 kHz in one turn.  To get 
10 Hz resolution, you would need to have an encoder capable of a 
resolution of 10,000 per revolution.  256 is about the highest 
resolution available, which means you will need to drive at least two of 
them, with a 40 to one reduction between them.  Or alternately, drive 
two 128 state encoders with the second  advancing every  complete turn 
of the first.  A third, and probably most  practical, is a 256 encoder 
with a 40:1 reducer on the  shaft, and a reset button to zero it at '000'.
I have considered a ten-turn pot coupled to a 16-bit A/D converter.  
Deriving both the A/D Reference voltage and the voltage across the pot 
from a single source may stabilize it enough to be practical.  
Unfortunately, you actually need an 11 turn pot to account for the 
overrun in the tuning (10.6 turns end to end).  Next, you will have to 
calibrate it for non-linearity, easily enough done through a table and 
interpolation.  And finally, add a thermistor to temperature compensate 
the 20ppm temperature drift of the potentiometer.  The problem here is 
that the cost would be more than a whole R-389/R-390/R-390A on the market.

mparkinson1 wrote:
> Hey guys I am looking for a PTO for a Collin R 389 receiver working or 
> not please I need one my receiver please email me off the list 
> mparkinson1 at socal.rr.com thanks.
> Let me what you have and for how much even a junker R 389 would work 
> for me with the PTO intack thanks.
> Matt Parkinson Military Equipment & R 390A Depot Center
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mparkinson1 wrote:
> Hey guys I am looking for a PTO for a Collin R 389 receiver working or not please I need one my receiver please email me off the list mparkinson1 at socal.rr.com thanks.
> Let me what you have and for how much even a junker R 389 would work for me with the PTO intack thanks.
> Matt Parkinson Military Equipment & R 390A Depot Center
> ______________________________________________________________
> R-390 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/r-390
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:R-390 at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
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