--- mch <[EMAIL PROTECTED]> wrote: > Joe, > > I think you forgot another likely reason: The HIGH > PASS FILTER in the > mic circuit. Like the high frequency energy, there > is also a lot of low > frequency energy (below 300 Hz) on simplex that is > being stripped by the > high pass filter in the mic circuit that ensures > CTCSS frequencies in > the user's voice don't false decoders or interfere > with the transmitted > CTCSS. I don't think that HPF is on the PL board on > a Mitrek, but I > could be wrong. I don't have any books at home right > now for one. > > I think your best solution is to run unprocessed > audio (no de-emph - no > preemph). If you do, most of your audio coloring > should go away. I don't > recall the audio chain of the Mitrek exciter, so you > may have to add > limiting and LPF'ing to the TX audio (Joe, weren't > you working on an > aftermarket board to do that?). I know in some > units, you can still use > the stock filtering, as the preemphasis (that you > need to eliminate) is > before those stages. Of course, this would only > apply to a FM exciter > (which the Mitrek is). It would not apply to a PM > exciter. > > Joe M. >
Yes, if there is an HPF in the mic circuit, it will likely be causing the problem you are describing. I just can't remember if the Mitrek has an HPF in the mic line (other than pre-emp). Yes, about a year ago I designed and built a clipper/LPF board that works great. Then I bought 4 new (to me) companies and have been busy with that. I have about a dozen of the boards ready to stuff, but I don't have the time to do it (probably takes 30 min per board). I have the first one I built running on the local 2M machine here, sounds great. These use adjustable "brick wall" type filters that are tunable with a pot from about 2500 Hz to 5000Hz cutoff freq. When set to 3300 Hz or higher, they seem to sound "transparent". I suppose for links you might want them set at 4 to 5 Khz. The filter is very flat from about 50 Hz to .9 Fc. At Fc it is 3 dB down, and above that it drops really fast. Joe __________________________________ Do you Yahoo!? Yahoo! Small Business $15K Web Design Giveaway http://promotions.yahoo.com/design_giveaway/ Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
