TopBand: TS940 CW filter performance??

[km1h @ juno.com]

Hi Mel, I own four TS-940's so here are a few comments.

I have never tried just a single filter, but from your description it
sounds like you just hit it lucky on the carrier oscillator slope. There
was a lot written in IRCI bulletins back in 86-87 or so about the
problems with sharp cascaded filters. I have found that by very careful
alignment of the oscillators it is possible to get  good CW performance
with the KW filters and excellent performance with the IRCI 400 Hz units.
My own experience is that the KW 500 Hz filters have more loss AND are
not as closely matched to the carrier frequency. 

IMD can be greatly improved by changing the front end RX filter diodes
over to PIN's. If you are really into some extra work you can change the
diodes in the IF that control filter selection plus the NB. The product
detector diodes can be changed to Schottky type (1N5711) for an
improvement in audio distortion. 

The 8M series is right where KW admitted the 940 had severe phase noise
problems and served up Bulletin 917. There are also AGC mods for narrow
filters and reducing the tuning rate to 5KHz per revolution.

Contact IRCI and order the set of 940  bulletins to get started. You will
note that serial # plays a big part in some of them but dont believe
everything. I have seen several 940's that were above the cut-off numbers
and did not have the factory mods. I have also seen several in the 8M
series that had only half of 917 installed and some not at all. 

The 940 also has connectoritis. Get a spray can of De-Oxit and some
Q-Tips.

GL and 73....Carl   KM1H   


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