At 11:33 PM 05/30/08, you wrote: >Hi All, > >I am trying to build a circuit to roll of the discriminator audio >coming out of my UHF Mastr II receiver. I have one of those >controllers that does "smart squelch" by paying attention to the high >frequency noise and it seems the Mastr II receiver does not have >adequate filtering to stop the 455khz IF frequency. > >The manufacturer says this is a problem they are aware of with Mastr >II's and recommends a 10 mH inductor in line with a 1000 pF cap to >ground to get the discriminator audio to roll off far under 455khz. > >Now, I'm pretty new at this so am not sure exactly what I'm looking >for in a 10 mH inductor. I have found locally some "high current RF >chokes" rated at 10 mH inductance, and when I search on Mouser for a >10 mH inductor it returns many thousands of results. The cheapest >thing I can find on Mouser is a tiny through-the-hole component to >mount on a board and has a small current rating, but I suspect this >would be fine for this purpose. > >Has anybody out there built such a filter to handle the 455khz IF >frequency in the Mastr II receiver before, and could you recommend >more specifically what kind of 10 mH inductor I'm looking for? > >Thanks much > >Mark Hagler >W7WMH Seattle
Someone is misunderstanding something. I have NEVER seen a situation where the IF frequency leaks into the received audio. And if it is, you fix the radio, not add a band-aid outside it. Anyway, if you are talking about rolling off the audio, or de-emphasizing it, read this article: <http://www.repeater-builder.com/tech-info/flataudio.html> Then this one: <http://www.repeater-builder.com/tech-info/fmtheorydiscussion.html> Yes, there is some repeated material, but when you have two people writing on the same topic some repetition is going to happen. Then this one: <http://www.repeater-builder.com/tech-info/pdemph-post.html> Mike WA6ILQ
