The filter gain compensation is -post- crystal filter. Its done inside the DSP.
If this is set well above what is really needed, the DSP may generate some distortion on really strong signals. We usually recommend +4 dB max. 73, Eric WA6HHQ William Carver wrote: > The "DUAL PASSBAND" makes a pass at providing an APF type of function > where you make the DSP passband as narrow as you choose, but there's a > wider passband that's 20 dB down. Undoubtedly it isn't the same shape as > APF amplitude v.s. frequency, but conceptually "a signal peak floating > on a sea of weaker undesired signals" is similar. > > G3XJP implementated a DUAL PASSBAND function (that terminology hadn't > been invented then) in his STAR transceiver, but there the amplitude of > the wider passband can be dialed to be -20, -30, -40, .... -60 dB. It > probably isn't too big a deal to make the "skirt attenuation" number a > user-adjustable variable but I enjoyed being able to dial it up and down > as QRM changed....which would ite up another programmable functio > button. > > For those who suggested kicking the gain compensation up when narrower > roofing filters are switched in, that's exactly what I did. I'm well > aware that IF the roofing filter is setting the IMD capability of > the receiver adding pre-filter gain reduces the intercept/increases IMD > WHEN that IMD happens to occur, and IF it happens to fall into the > passband with the desired signal. I intentionally emphasized the string > of IF..WHEN..IF.. because depending upon you penchant for living in > pileups, or turning the rig off on big contest weeks, a 4 dB IMD > increase IF all of those things happened to occur may, or may not, be > that big a deal. > > A post-roofing filter gain increment would not affect intercept or IMD > and could be a smoothly varying increase that could conceivably be > matched to a users memory of APF or Heath QF-1 function. > > Bill > _..._ ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
