Re: {Collins} KWM-2 selectivity alignment



The basic answer is no.  The selectivity is set by the mechanical filter and
there is only one that serves in both Transmit and Receive.  If that rig is
wide in receive, it is also going to be wide in transmit.

The bandwidth should be 2.1 KHz in both receive and transmit.   You can get
a good sense of what the bandwidth is by using the calibrator.  Turn on the
calibrator and tune the dial to any even 100 KHz mark. Peak the S-Meter
reading by slightly tuning the dial around until max after peaking the
Exciter Tuning too.  Then note frequency. The S-Meter should read around
10-15 db over S-9 on 75 meters.  To make it easy, then just tune the
preselector (Exciter Tuning) until you get 10-15 db over S-9. Now turn the
dial up in frequency until you see the S-Meter drop JUST to the noise floor.
Note the frequency.  The go back and go below the noted frequency until it
again falls just to the noise floor. Subtract the low reading from the high
dial reading.

That result will be roughly your 60 db Band Width for the filter.  It should
be around 4.5-5 KHZ...as measured   This is a VERY rough way of doing this
so close is good enough.

The 6 db BW (the number usually quoted as the BW for the filter) is 2.1 KHz.
The 60 db BW should be around 5.3 KHz if the filter is happy.  Measuring in
the drop in signal from S-9 +10-15 db will give you a sense of the  60 db BW
and should be just less than the stated 5 KHz.  

If the measured BW is much more than this, then you have a damaged filter or
you have a wiring problem.  Of course you are aware that the filter is used
- and the same circuit is used - in transmit. so if you have a bandwidth
problem, do not use the transmitter until you get it fixed.  Your SSB signal
will be very wide.

Good luck Peter and let us know what you find.

Regards,

Bill

Bill Carns, N7OTQ (Trustee K0CXX)
Past President, Collins Collectors Association
Founding Board, Collins Radio Heritage Group
Editor, Signal Magazine (Retired)
Wimberley, TX
512 618 2762  (Cell)
512 847 7010  (Home)





-----Original Message-----
From: Collins [mailto:collins-bounces+wcarns=austin.rr.com@xxxxxxxxxxxxx] On
Behalf Of Peter Ravn via Collins
Sent: Sunday, November 05, 2017 1:29 AM
To: collins@xxxxxxxxxxxxx
Subject: {Collins} KWM-2 selectivity alignment

Is there any way of adjusting/improving the selectivity of my winged KWM-2
which seems too wide on all bands?

Thanks.

Peter OZ8CTH

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