[TMC] GPR-90 Alignment

[MIKE SOUHRADA]

Telegrapher@worldnet.att.net wrote:

> "sweep" method for the IF's.  How do you use the "sweep" method if they
> don't give them to you in the book?  Or is this something everyone
> should know anyway? 
Larry
You are further ahead of the GPR90 game than I. But I did notice that terse
instruction on sweeping the frequency. Fortunately I have a sweep 
generator with no instructions. However I understand the gist of it;
which is:
Instead of just plugging in a fixed frequency and tuning for a peak;
a sweep sends a spread of IF signals to the scope when hooked up 
properly. Thus you can see the passband change as you align the unit. 
Figure 5-2 in the manual shows an upside down passband. You should see 
that on the scope.
The Hammarlund HQ180 manual shows a similar diagram. This allows
visual observation and how the curve peaks or shows a flat top.
My sweep is a Precision E 410 but I've never found a manual for it.
The HP sweep units might be better.
My voltages are really off and for that reason my alignment is not
done yet. Might be my IM 18 needs tweaking.I must say though that
the current alignment is extremely good after 45+ years.

> I also notice that when i use the xtal calibrator, 
> quite unstable.  Like something is intermittant. 
I really doubt the slugs are unstable. I had noticed an apparent lack
of audio volume in mine. So I gave all the band switches a good bath
in 99% alcohol  and volla! just about everything came up very strong.
Also noticed a nib on the front band switch was not properly installed.
It was one of the lower bands. The wiper was OVER the nib and not
passing through the two nib contacts. You might want to check yours.
I've only seen that once before on a Drake. That was really a bad one
only one nib touching and not very well.
One other thing I noticed was the chassis tends to bend. I noted
three screws were broken , replaced those. I suspect there are some
more grounds in my unit that are not making good RF contact.
Had a real peculiar situation identical to that with a HQ 180AC. Screw
direct to the chassis made a DC contact but not a RF in the local 
oscillator stage.Took a long time to find that.
Mike
Iowa
> Larry
> W0OGH