[R-390] R-390 Related Activities

[Tom-WB3AKD]

Mechanical Filters:

Well, finally found a cost effective 8KHz filter for the -A and swapped it
out.  This offered the ded one for tinkering so messed around with some
graphite (all kinds of blacl dust) and came up with a crude resistance
soldering setup to open up the dead filter.  As was explained on this list a
while back, the wires were indeed broke, and the foam was real gummy.

Took the filter out and gently cleand the majority of the gunk off it,
removed the paper and remains of the foam and cleand the sticky stuff out of
the tube with IPA.  Lined the tube with Kapton Tape, then took some newer
foam and cut then wrapped it around the filter and put the whole thing back
together.  Swept it with the HP3336B with initially satisfactory results (no
resonating capacitors on the filter so its pretty bumpy in the pass band
right now, and I am not presently presenting the right impedance).  Still,
positive results so far.  The plan is to sweep it some more with the proper
terminations and then see about sealing it up after a little baking to
remove the moisture.  An interesting experiment.

390 swept alignment:

Probably no news for most of you here but having done the "manual" IF
alignment some time ago and having the sweeper hooked up, I muscled the 390
over to the bench and swept it.  I found the shapes to be unsat so went
through the procedure with the sweeper:  Moved the LC pass bands over to
where the crystal filter was centered then tweaked the shapes up a bit.
Much nicer sound now.  I am now fully sold on the sweept procedure.

73

Tom

WB3AKD