[CQ-Contest] SSB filters for Kenwood TS-940

[W2RU - Bud Hippisley]

At 05:34 2005-02-25, Rick Bullon wrote:
>I already have an Inrad 2.1 for the 8830 IF [in the TS-940] but I would like to know the 
>thoughts of the list on which to install in the 455 IF. I checked the Inrad 
>site....the choices are now 2.1 or 2.8. So would I want the same filter in both 
>slots or do I want the wider filter in the 455 slot?

Rick --

I can't think of any reason to put a WIDER filter in the LOWER (455) IF.  In your scenario, the signals coming out of the high IF are going to be bandwidth limited by the 2.1 kHz 8.8 MHz filter you already own, so a 2.8 kHz filter in the low IF is only going to pass some added internal stage noise outside the range of desired signals from the high IF.

It's been my experience on the TS-940 and the TS-950SDX that using identical bandwidth filters works best.  On the 950SDX you can front-panel select the high IF and low IF filters independently, so I've had some opportunity to play with deliberate mismatches.  In my opinion, the VBT works best when the two filters are the same bandwidth.  On both rigs there appear to be some combinations of different bandwidth filters for which the microprocessor-controlled VBT steps don't properly track.

By the way, if you go ahead and buy a 2.1 kHz filter for the low IF, the net effective bandwidth of those cascaded filters will be less than the bandwidth of the narrower (or both) filters, so you might have an effective BW of perhaps 1.8 kHz -- which is a fine value for our HF phone bands.  And on CW, even though I have matched 500 Hz filters, I prefer to run with my SSB filters and use the VBT to bring the effective BW down to about 1200 or 1000 Hz.  That's probably because on my CW traffic nets not everybody can zero-beat the NCS perfectly and because when I'm in contests I like to listen to the contest QSOs on either side of the station I'm working.

The one exception I'd make to using identical filter bandwidths is in the case of the 270 Hz CW filter for the low IF.  That combines fairly well with a 500 Hz filter in the high IF.  However, if you really do need the super narrow CW filtering (low end of 40 meters in a DX contest, for instance), it's always best to do it as close to the RX antenna input as possible, so my first choice there, too, would be matched 270 Hz filters in the high and low IFs.

Hope this helps.  Good luck.

73 -- Bud, W2RU