SX-28 Crystal Filter Alignment

[Brian Sherwood]

I've never found a comprehensible procedure, not in any of my BA manuals nor
in the Sams photofact for the HQ129.

What I've always done, is couple a sweep grnerator into the rf input, hook
the scope's vertical input to the last IF output, hook the sweeping voltage
to the horizontal input, thereby developing an on-screen display of the IF
strip's bandpass, and from there it's pretty simple to twiddle cores and
trimmers until the 'phasing' control is balanced at 12-o'clock [when the
notch goes away and the overall bandpass tightens way up].

50's-early-60's-era ARRL handbooks actually explain 'single-signal reception
with crystal filter' the best of all available resources IMHO...

BUT do make sure you check out
http://groups.google.com/group/rec.radio.amateur.boatanchors/msg/145c0341600
3c51d

73 de ka9egw

-----Original Message-----
From: Boat Anchor Owners and Collectors List
[mailto:BOATANCHORS at LISTS.TEMPE.GOV]On Behalf Of Lin Robertson
Sent: Friday, December 12, 2008 10:41 PM
To: BOATANCHORS at LISTS.TEMPE.GOV
Subject: SX-28 Crystal Filter Alignment


Am in the process of doing a full alignment on a SX-28 via the instructions
on BAMA by N6PY (SK), which he wrote to eliminate some confusion in the
SX-28 manual instructions, which are none too good; unfortunately,
paragraph one of Step 3 seems a bit confusing _itself_, and I was wondering
if someone could clear this up:

============================================

"Switch to the crystal wide selectivity switch position. Turn off the
modulation of the signal generator but leave its output level set to the
crystal's frequency you found in Step 2 to get around a -5V reading. Turn
the receiver's audio to hear some hiss in the receiver. (Here it comes.)
Keep the phasing set for maximum selectivity _in crystal filter sharp_."

============================

Uh, is it just me, or does the last sentence contradict the first
sentence?  I mean, first it tells you to set to xtal wide, then it tells
you to KEEP the selectivity switch in SHARP, as if it were already there.
(??)  Which is correct?

[I tell you, I've been aligning HF RX since 1968, and this 28 Xtal Filter
procedure (both) is driving me bonkers. I did a SX-28 once 20 years ago,
and I think the memory of it was so bad I think I blanked it from my
mind.  The HQ-180A procedure is a marvel of clarity compared to it.]

In any case, if anyone can throw some light on this, it would be MOST
appreciated.  It's probably very simple, and I just probably developed a
mental blind spot from dwelling on this for so long.

Many Thanks to the group in advance,

Lin/KJ6EF

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