[R-390] Antenna Trimmer

[Roger Ruszkowski]

Steve,

Worry not where the knob points.

Every alignment step says twist the knob for max every time you 
change the receiver or signal generator.

In the R390 manual TM 11 5820 357-35 there is a procedure to set the first 
cap in the RF deck octave cans. 

This procedure is not in the R390/A manual TM 11 5820-358-35

That procedure says worry not where the antenna trim trims to,

The reply that you should expect two peaks on the trim is true.

As you rotate a cap from full mesh to no mesh you can dial it 
clock or counter clock wise. So you expect two points that reach peak trim.

The TM said mix two caps and a slug for best pass. In fact the R390
TM says balance the first cap for minimum response 

And the adjust the slug, second cap and trim for maximum
response.

Not getting two peaks on the trim may have more to do with the 
antenna / signal generator coupling than alignment or circuit operation.

The TM say use a pair of 68 ohm ( 47 - 120) resistors in parallel from the 
center conductor of the signal generator with one each resistor feeding each side
of the balanced input. Ground the coax to the chassis.

Use lots of drive this is a very lossy process.

Then the front cap in the RF can will vary the receiver output.
I adjust for maximum output. 
The TM does call for minimum output.
We always though this was a TM misprint.
The antenna trim should let you peak this balanced input.

Try adjusting the first cap and the trim with this balanced drive
across two resistors and see if you find a bast peak of trim and cap adjustment.

Remember the slug gets set with the second caps And these may both
need a re peak after you get the front cap set.

Feel free to repeat this whole RF deck alignment as many as three time
or more from end to end not counting just going back as you do each octave.

If you change some tubes, you may want to re align the RF deck after you get
600 = 700 hours of power on time on the tubes. (24 7 for a month)


There is nothing in the TM about where the knob should or should not point 
when you reach peak. We never tried to set the Antenna trim knob.

Once you go back to an unbalanced input there is no guessing where
the trim will peak as the antenna impedance and receiver impedance varies across
the frequency of interest.

Hope this helps.

There is a long large inspection procedure at R390.net and hosted by other 
R390 Fellows on their web pages that details the use of the resistors and alignment
procedures.

The R390 TM is on line as a PDF file and you can down load and read the
original procedure in that manual.

Roger

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