[R-390] Receiver peaks off the m/c band detents

[Tim Shoppa]

VE3AJM asks:
> Anyone on the list ever dealt with a 390A where
> the receiver peaks off the m/c band detents. It
> occurs on most of the bands, some more than
> others. I have done a complete mechanical
> alignment of the receiver, so I know the cams,
> crystal oscillator and bandswitches are aligned as per
> the manual. The slug racks and the slugs all move freely etc.

The RF slugs/coils aren't tracking perfectly.

But this is not necessarily a failing.

They never will be tracking perfectly across all the bands,
but they should match up at the frequencies where you
aligned the RF deck. e.g. if you iteratively adjusted the
slug position and the trimmer cap adjustments on the
8-16Mc band, then it should be set up correctly
at 8800 and 15200kc. If this is severely out of whack,
then maybe a gear slipped since alignment.

Each can has two degrees of freedom (slug and trimmer) in
aligning each RF band, so you can't expect it to peak
on every single frequency throughout the octave.

Bad/wrong coils, or coils that aren't fully seated, or (gasp!)
coils with broken forms can make tracking far worse than
you'd expect.

Others here have suggested modified procedures that
involve iterating other than the two "official" per-band
frequencies to use all six degrees of freedom available
(three trimmers, three slugs) for each RF band.

Contrast with the PTO corrector stack where there are
dozens of little correctors for each segment of the PTO.

Wrong slugs will cause tracking to be much less than optimal
(usually you can't align the band at all with the wrong slugs).

Tim.