Hello Ron, The audio emphasis for FM is a different issue. When I put the discriminator output from the Mastr II receiver on a analyzer you can clearly see a spike way out at 455khz which I believe is the IF frequency in the receiver.
This controller has a auto-squelch feature (it does not use a COS/RUS line at all) and it listens for the presence of high-frequency noise coming off of the receiver to control the squelch. When a nice, full quieting FM signal shows up the high frequency noise goes away and the controller will detect this and kick on the transmitter. This detection circuit is behaving poorly on the Mastr II because this strong 455khz component is throwing it off and making it shut down the squelch because it thinks there's a lot of high-frequency noise even when the signal is actually full quieting. Running the audio through a 10 mH inductor tied to a 1000pf cap to ground should cause it to roll off the very high audio frequency and solve the problem.... but here's what I run into trouble, there's thousands of parts out there that say "10 mH inductor" so I'm over my electronics head now! Thanks, Mark Hagler W7WMH Seattle --- In Repeater-Builder@yahoogroups.com, Ron Wright <[EMAIL PROTECTED]> wrote: > > > Mark, > > Not sure what the manufacture is talking about. > > I think your problem is at the audio level, not 455 kHz. > > Sounds as if you are taking de-emphasised audio which has a roll up of 6 > db/octive...with same deviation coming in as you double the mod freq you > double the amplitude. This give "tenny" auido, lots of highs. It is > what comes out of the MII discrementator. > > You need a 6 db/octive circuit to compensate for this. Try this > circuit: > > http://www.n1uec.org/n1uec/deemphasis.html > > I've used similar (.01 cap instead of .0068 and a few other component > differences). You will see a world of difference. > > 73, ron, n9ee/r
