[R-390] Stinkin' PTO !!

[Phil Atchley]

Hi John.
Yes I have a similar box that I built, perhaps a little more elaborate.
Mine is in a double shielded box and generates markers at 10. 5, 2 and =
1MHz
as well as 200, 100, 50 and 25KHz, switch selectable via a rotary switch =
the
actual switching done through CMOS switches so I can run just DC control
lines into the "inner sanctum".  The output level is variable by a
Potentiometer that feeds a 10dB pad to insure a pretty decent match =
(20dB
return loss minimum) to 50 Ohm receiver inputs.  It has aligned many a
receiver!  Right now I think I have a one or two bad CMOS switches as =
some
ranges don't work, although I can get 25 KHz out of it indicating all
dividers are working properly.  Luckily all IC's are socketed!  The =
thing
works surprisingly well!

However, to align a PTO it is much easier to use a counter (best) or
"standard" receiver as the PTO is a generator in its own right.

73 de Phil, KO6BB
DX begins at the noise floor!
k06bb@elite.net
Merced, California
37.18N  120.29W  CM97sh

-----Original Message-----
=20
On Sat, 28 Jun 2003, Phil Atchley wrote:

> Good afternoon all.
> Well, the odyssey of the Cosmos PTO lives on.  I repaired the end =
point
coil
> this morning and was able to set the end points F.B.
>
> However, earlier when I checked the linearity at the 100KC points it
looked
> 'pretty good, running typically 200 CPS to 1 KC off.  However, the 600 =
KC
> point was OVER 2 KC out and I figured I could correct this with the
> correction adjustments.  WRONG!

I should repeat a tale I've relayed once or twice before -

I once had a National HRO-500 which was rather beat up.

Some previous owner had adjusted the tuning linearity until
it was perfect NOT. Indeed it was on on the 100 kHz calibrator
points and 25? 50 kHz? However between calibration points
it was as much as 5 kHz out. Looking at the slotted end plate
of the tuning cap, it was bent up to look like a saw blade
/\/\/\.

To tweek it back into shape, I built a neat little crystal
calibrator box. Starting with a 4 MHz crystal oscillator,
I went through a chain of divide by 10 digital dividers,
with a switch to select a tap on the chain, and then a
chain of divide by 2's, also switch selectable. Thus I
could select 4 MHz, 400, 40, 4 kHz, or selecting 400 kHz
switch in divide by 2's to get 200, 100, 50, 25, 12.5 kHz
or selecting 40 kHz, get 20, 10 5, etc. This gave me a
real multitude of spot frequencies to check the dial at.

A perfect square wave would have only odd hormonics in
the output. If you instead of a square wave out of a
crystal calibrator, generate a very narrow pulse, the
od and even hormonics will be almost even in amplititude.
The narrower the pulse, the higher higher frequency output/
Using 74S logic, the output went to almost 100 MHz before
starting to fall off.

With as many adjustment screws as the Cosmos PTO has, it's
necessary to check at freqs other than the 100 kHz xtal
calibrator spots. Such a unit as I've described would be
ideal. With the high speed digital logic available nowadays,
it could be made flat to very high freqs indeed.

John





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