[R-390] Collins R 389 PTO

[Bill Hawkins]

Not a problem. Do what the Navy did 60 years ago for accuracy from
synchro angle transmitters. When the antenna or gun turret turned,
it turned the coarse 360 degree synchro. Another synchro, geared up
1:10, provided 36 degree resolution.

The PTOs are multiturn, so we'd need to gear down rather than up.
The first 1024 encoder is the fine encoder. It turns as the shaft turns,
so it can't have any stops. The coarse encoder is geared down from the
shaft by 10:1 or 50:1 to match what the RF deck does. Actually, the 
encoder resolution can be reduced to 256, which is less expensive.

The gear train is not complex, unless your only tool is a soldering
iron.
Most analog clocks have a couple of 12:1 gear trains.

Maybe this would work with a 16 bit DAC and a volt to frequency chip.
No sine waves, though, unless there's a square to sine converter chip.

Does a mixer followed by a selective IF amp need a sine wave? Could
have image problems, but there's two tuned RF amps in the 389 and 90.

I'd like to work on this and share results, but the previous
administration
cut my net worth in half so there's no time for play.

Bill Hawkins


-----Original Message-----
From: DJED1 at aol.com
Sent: Monday, May 04, 2009 12:49 PM

Another PTO wouldn't work because of the 50 turn requirement, unless you

geared it down.  But then the non-linearities would be 5 times worse.   
(Maybe that's better than a dead radio).
I thought about a DDS replacement for my R-390A, (it would be nice to
get real 100 cycle readout accuracy) but the biggest stumbling block was
the lack of  a 10,000 count encoder.  The best available seems to be
1026, and so that  throws you into dual encoders and a complex gear
train.  But if you could  get it going then the mechanical dial and
calibration would all still work.  The other issue is some way to
remember the frequency setting with the power off- probably not a big
issue.  The complexities of a microprocessor controlled DDS are beyond
me, so I dropped the idea.  It  would be nice if someone would tackle
the problem and share their results.
Ed  W2EMN