[Collins] KWM2A receive alignment - USB/LSB

[Fern Rivard]

    As per your report on the frequencies of  both the USB and LSB 
crystals, I would recommend that you replace both of them and if still 
having some problems with the frequency response to then replace the 
collins mechanical filter.
73 from Fern  VE7GZ



----- Original Message ----- 
From: "Gerald" <geraldj at ispwest.com>
To: "Steve Garwood" <n0czv at willard-oh.com>
Cc: <collins at mailman.qth.net>
Sent: Wednesday, February 01, 2006 11:56 AM
Subject: RE: [Collins] KWM2A receive alignment - USB/LSB


> 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
>
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