At 1/27/2007 18:37, you wrote: >>the circuit I've been using is at >><http://www.tasma.org/micorsq.png>http://www.tasma.org/micorsq.png. >> > >I see some potentially major problems with the TASMA circuit, as it is not >a replica of the OEM Motorola circuitry; like the one I provided.
That circuit is essentially a copy of a circuit designed by Bill Wood W6FXJ (ex-WB6FXJ) of the Goldstone ARC/JPLARC in 1979. Bill also included some active pre-filtering which I later determined had no effect. As far as the other differences go, I've never analyzed them in detail but knowing Bill, he wouldn't make a change without a good reason. I suppose I should send him a query sometime & find out just what his reasoning was for the changes. I never thought pin 10 was ever intended to drive a squelch gate. The one thing I like most about the Micor squelch is how fast the decay time is for strong signals: at around a millisecond or two, it's even faster than the Mastr II fast squelch. If it's done right (not just the circuit itself but the audio gating as well - no "pops") & the user doesn't have a "dirty" unkey, you almost can't tell when the user stopped TXing. Of course now with ADMs abound, I guess the squelch decay time isn't as important anymore. >inconsistent with the OEM Micor circuitry. Maybe they don't make that >much difference in real world use, but I'll bet my money on the original >Micor circuitry. > >YMMV... >Kevin FWIW, the adapted FXJ Micor squelch circuit is in use on at least 7 systems here on 220 & 440 MHz & has worked quite well for us. The power supply filtering on pin 9 could be improved, though I think it was assumed that the power was from a "clean source", & in many cases is actually from the regulated 10 V bus of the G.E. MVP. Bob NO6B
