| Matt... I use an MFJ 784B, Tunable DSP Filter. It takes the audio from your rig as input. You can vary the filter frequency as well as the band width. It has several preset filters already built which are selectable with a rotary switch. Also provides dual freq settings/notches etc which can be used with RTTY or other multi tone modes. I find most of the time I can leave it set to a very wide bandwidth and get the filtering I need... As with any audio filter, if you titen up the bandwidth too much it gets a little "ringy" This filter also works with ssb... It has AGC, and noise reduction, as well as auto-notch modes. You have to provide it a speaker (I built one in). This filter works well in cases where you don't have, or can't get, an IF filter built into the rig. Its very versatile... I keep it in the audio out line of my homebrew qrp rig... I usually just use its audio amp, but being in line its immediately available as a filter when I need it, at the push of a button. |
