[R-390] Alignment questions

Sat May 7 21:46:10 EDT 2005

Barry,

You are thinking to hard.
I hope the following diatribe is helpful.
If something just does not make sense, post some more questions.
I retired because my senior moments were becoming problematic.
Retirement did not cure the problem.
I just am not making statements in retirement that impact peoples lives.
I may be screwing your hobby up, but you will have time to recover.

--------------------
Should the PTO be set to accommodate the off-frequency of the
17mc oscillator? 

Answer NO.
-----------------------------
PTO won't always track between 3.455 and 2.455 exactly, what do We do?
Answer  Set Zero adjust to center Set dial to 500, Set PTO to 2,955,000.
Lock the clamps.

-----------------------------
Is this a good method?
To do this, I can loosen the clamp from the Oldham coupler
to the front-panel shaft, dial in a known frequency (say my 770kc station),
set the BFO to 455kc, and while holding the dial at 0.770kc, rotate the PTO
shaft to zero-beat and retighten the clamp.  

Answer NO.
---------------------------------------------------

Set the PTO for 3.455 or 2.455 Smack in the middle of the zero adjust.
Use the frequency counter. Remember you want it to work with some 20 crystals
and their harmonics. You may never get the PTO to exactly 1 Mhz in ten turns.
Just do the best you can. Then have it spread both ways from center by 
setting it up at 500Khz rather than at either end point.

---------------------------------------
When using a broadcast signal (good idea because we know what the frequency 
is),
during alignment process.
Set the zero adjust to calibrate on the nearest 100 KC.
#### 
This operation dials in the crystal offsets.
Set the bandwidth to .1Khz (to get into the center of the filters)
Set the BFO to zero (in the center of the IF deck filters)
The 100Khz crystal has a 320 plus harmonic that is close at 31.000+
The PTO is then beat with all the mixers to get into the middle of the band 
pass.
The act of doing a cal zero at the closest Khz marker dials all these offsets 
in for you.
########################

Roll the receiver counter to the same frequency as the signal is on.
Now rock the Khz knob for the best peak output you can get.

This will get you around the offset of the fixed crystals on any Mhz.
Believe this is close, remember  it has worked for Army tech for the last 40 
plus years.
Now tweak the thing to be peaked at the frequency you are on.

Skip trying to inject frequencies any where except the antenna input.
If you are aligning the first and second mixers second IF's.
Use 10 uv or less of RF at the receiver dial reading into the antenna input.
Use the frequency setting in the TM for the dial read outs.
Adjust the item you need to adjust.

For the Second variable IF Para 75 page 116. it says.
Set the receiver to 1.900
set the signal gen to 2.1
Inject the signal at E210.
Adjust the 3 slugs in Z216 cans

Really do the following
Set the receiver to 1.900
Do the receiver Cal at 1.900 (a calibration point)
Set the signal gen to 1.900
inject the signal into the antenna input.
Rock the receiver to max signal or rock the signal generator.
Adjust the 3 slugs in Z216 cans

Remember symmetry. If you are doing an alignment 250 off one end, then you 
want to be 250 off the other end for the matching alignment. (off the other end 
is likely 750, because its below the end)

The TM says find the nearest 100KHZ and zero adjust.
Then it says rock the AN/URM25 to exact frequency.
You are not going to rock the AM station, so you need to rock the receiver 
dial to peak.
-------------------------
Investigating this, I found the 17mc oscillator is 16.997mc.

Buy doing a calibration zero at 100Khz closest to the alignment frequency 
before injecting a signal and doing alignment, you factor this variation into the 
receivers alignment.

Trying to peak all the RF deck over a 3,000 cycle crystal shift is not going 
to make a performance difference in the receiver. We know these crystals are 
not super exact, which is why you want to inject everything at the antenna. Do 
the calibration zero beat against the BFO into the middle of the  .1Khz 455 
Khz IF before each tweak. Then set the dial where it belongs and then peak the 
innards to perform.

Then when a signal comes in the antenna and we peak it max, the dial should 
read the exact frequency we expect it to see.

I watches a lot of guys try a lot of thing over several years. Tried a bunch 
my self. The approach above works the best. You can get some frequency to Max 
out buy playing around. But it will cost some where else. We had 4 or 5 guys 
working 2 receivers per 8 hour shift. three shifts a day 365 days a year. We 
had time to try all kinds of stuff. Any and every variation was talked about. 
Some real tech wizards though about this stuff. I had techs with math degrees 
drafted to be receiver repair guys. We had some other guys who were detailed to 
clean dust out of fans, some more that were just allowed to push a pencil. 
Every one was not equal in creativity. But over the years some real sharp guys 
with lot of time on their hands considered what was going on.

The TM procedure is pretty good.
The mid point alignment procedures are really needed if you have a dead 
receiver or a marginal problem and you are trying to decide if you need to re 
replacing, cans, slugs, caps, or other nasty subtle problem. So the TM is the over 
kill cover every thing approach.

For a good receiver just needing a good alignment, there are ways that get 
better results with less work. You try to do a real PM on your receiver in 4 
hours. You are humping it. This is why we did them two at a time. Once you were 
dusting you dusted 4 or six, while your buddy shoved a bunch of tubes through 
the tester. You would be cleaning away and some guy would walk up and pop your 
3 6C4's out and walk away. Soon he would bring you back 3 tubes plug them in 
and pop out some other tubes. If you were doing tubes you would grab all the 
6C4 and test them all. The best would go back and you tried to put all the new 
tubes into one receiver. That receiver was noted on it PM record. In the  next 
monthly you knew it would need alignment. The other 3 or 5 receivers would be 
OK in the monthly with well broke in tubes. Coming out of cleaning, someone 
would do the Calibration zero, BFO and PTO with the frequency counter. The rest 
of the alignment was done against the BFO, PTO and cal or the receiver. You 
could do 2 receiver by your self in 8 hours, go to lunch and do a couple trouble 
calls.

-------------------------
One more question:  For aligning the second IF, the manual states to set the
signal generator to 18.750mc and the R390A to 7.250mc.  

I think this should  be 18.250 & 7.250.
Is this a known issue with the documentation?   NO.

Remember you are doing a difference in this mixer. you are 250 off the ends.
One way is 250 the other way is -250 = 750.

What you really want to do is 
Do the calibration zero adjust at 7.200 or 7.300
Then just insert 7.250 into the antenna input.
Let the mixers mix it with all the small offsets.
Tweak the proper item to get the best peak you can get.

Trying to  re zero, insert things in the middle, compensate for some item 
just drives you to distraction.

You want the receiver to perform the best it can on all frequencies.
All frequencies may not perform equally well.
But not because the receiver is not properly aligned.

Get each setting as good as you can.
Repeating the whole process 3 or more times will bring improvement on each 
pass.

Realignment after changing a tube, may or may not bring an improvement.
The old and replacement tube may be very equal in distributed capacitance and 
gain.
The first 100 tube you try may all peak exactly the same. Then boom the next 
time you stuff a tube in, it will need a different alignment.

Let the receiver run 24 x 7  and do a realignment of the RF deck. 
You likely will not need to do the BFO and PTO settings. Things seem to 
change with a little burn in time. We use to re align the receivers the first 
monthly TM after a semi annual PM and see some improvements. Enough to make it 
worth doing.

--------------------------------
I used my frequency counter, tuned the PTO to
the desired frequency (3.455 - 0.770) for a strong local station on 770kc
and set the BFO to 455kc.  At this point, the heterodyne theoretically
should have been zero; however, I was hearing a very high-pitched
heterodyne.

Investigating this, I found the 17mc oscillator is 16.997mc.  This (along
with any inaccuracy in the second crystal oscillator frequency) is the cause
of the non-zero beat.

This is why you do a calibration at the nearest 100Khz and move the zero 
adjust where ever it is needed to get a zero beat in the middle of the IF band 
pass.

This is why you rock the AN/URM 25 to zero. The TM suggest the problem is the
signal generator. You are not rocking an AM station to zero, so rock the 
receiver dial to zero. 

The alignment points in the TM are not set in stone. They are some good point 
on the band width slug rack position to give good performance. Just get close 
to the frequency and peak every thing up. The TM says rock the generator. You 
can rock the receiver much easier and get just as good an alignment.

Good Luck with this Barry,

Roger KC6TRU