[Collins] KWM2A receive alignment - USB/LSB

[Gerald]

On Wed, 2006-02-01 at 12:45 -0500, Steve Garwood wrote:
> I haven't checked on the center frequency of the filter yet.  I'll be
> setting up the signal generator - I would like to try the 10 pf across the
> crystal leads with clip leads just to see what difference it makes.  Part of
> the problem now is that I can take the measurements but I'm not able to
> affect any change.  Shifting the crystal frequency a bit would shed some
> light on things.
> 
> Steve, N0CZV

Its not only center frequency, its tilt of the pass band, or excess
ripple at one part of the filter pass band. You can do a decent check
with the receiver and calibrator along. Take your readings from the S-
meter and you tune the receiver past the calibrator.

Its unlikely the filter elements have changed frequency. Its more likely
that coupling between them which is by wires spot welded to the
resonators have come loose and affect only a part of the passband. Since
the response curve is inverted for LSB compared to USB a tilt in the
response curve gets an acoustical sound of strong highs on one sideband
and weak highs on the other. BFO shifts  (which typically are set 20 dB
down the response curve) add or remove mostly bass pitches by shifting
the filter sideways, with little perceived change on the highs because
100 Hz shift changes the low cutoff from 300 Hz to 400 or 200 Hz, but
the high cutoff from 2400 to 2500 or 2300 Hz which is hard to perceive.

-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer