[R-390] Collins R 389 PTO

[Mark Huss]

There was a government mod that implemented a digital display for the 
r-390 series.  Can't remember much details except it involved mixing the 
three local oscillators to produce an easily countable frequency.  
Perhaps Flowertime remembers.  Today, it would be much easier to just 
tap the three local oscillators output via a small coil around each 
oscillator tube, run three separate counters, or just one multiplexed 
counter, then do the math before displaying it.  AADE actually makes a 
three input frequency display suitable with a bit of reprogramming.  The 
issue is noise.  everybody who says they have tried it have reported 
problems.  Shielding may take care of this issue, though I suspect it is 
digital noise being fed back to the oscillator taps.

Gord Hayward wrote:
> If you are going to solid state the PTO, why not solid state the 
> frequency readout too.  A
> thin LED or LCD display running off the microprocessor could fit into 
> the current bezel
> which would make the mod reversible.  That would enable a simple shaft 
> encoder to give
> the required accuracy, and turning it fast would give a fast mode (lots 
> of kHz/click) change
> and slow (a few Hz/click) would give better  resolution.  Then, 
> non-linearities are irrelevant.
> Do I get burned at the stake for this suggestion?
>
> Cheers, Gord, VE3EOS
>
>