Q I use an IC-706 MkII on PSK31. I operate the rig in the upper sideband mode (USB) mode, but I wish there was a way to switch in my narrow RTTY filter while in USB. Can this be done?
A Yes, it can. To use narrow filters in the SSB mode, you have to fool the IC-706 into “thinking” that you’re selecting a narrow SSB IF filter when you’re really switching in a narrower 500 or 250-Hz filter.
With your 706 off, push the LOCK and POWER buttons together to access the setup menu. Let’s assume your 500-Hz filter is installed in filter slot number 1. Select menu item 19 (OPT. FIL 1) and select the filter FL-223. You are effectively telling the radio that you have installed the FL-223, a 1.8 kHz filter, in that position. Of course, that’s a lie! When you are operating in the USB mode and press the FIL (filter button), the IC-706 will activate whatever filter is in that slot. In this case, it will be a
500-Hz filter.
Still with me?
Once you’ve activated the narrower filter you’ll need to adjust your IF SHIFT control to place the PSK31 receive signal within the narrower IF passband. If you’re using the PSK31 software center frequency default of 1000 Hz, try setting the IF SHIFT control to the 1 o’clock position.
From QST October 1999
