wa9zzu wrote: > --- In Repeater-Builder@yahoogroups.com, "skipp025" <[EMAIL PROTECTED]> > wrote: >> Re: Reverse Burst Comments (Com Spec RB-1) >> >> If you add a circuit like the Com Spec RB-1 board to the typical >> repeater system using a ts-32/ts-54 board... the tx ctcss is not >> disabled or removed before the RB-1 delayed ptt line drops. >> >> So you have the phase inverted ctcss present for at most up to >> 200 ms typical before the tx drop. If you don't remove the ctcss >> source the inverted ctcss remains up until the tx off/drop... >> >> Any of you actually running the RB-1 board with a true reverse >> burst type ctcss decoder (built into your radio)? Is a true >> reverse burst decoder in your commercial radio completely "fooled" >> by the phase inverted ctcss before carrier drop function. >> >> Or do you actually still hear some minor difference from the >> rb-1 type operation vs an original true Motorhead (Motorola) >> encoder - decoder operation? >> >> Thinking out-loud about having to possibly mute the ctcss at some >> time after invert and before the delayed ptt drop as a requirement >> to get the full/true reverse burst quiet squelch close. >> >> Any of you been down that road already? >> >> skipp >> > Skipp, > I find your comments interesting in that the purpose that Motorola > had in using "reverse burst" of the PL tone was to quickly damp the > mechanical reed in the PL decoder to close the squelch and eliminate > the user from hearing the noise burst. But of course you knew that. > However, in later model radios there is no mechanical vibrating reed > to abruptly dampen and stop the vibrating from being detected. So > where is the need for a inverted burst if there are no receivers > using mechanical reeds as PL tone decoders? > Incidently Motorola did not use an inverted reverse burst of 180 > degrees. Their designs used 270 degrees since the PL reed then > stopped vibrating faster and the amplitude of the burst was also > increased to hasten the reed to stop. > Don't modern day receivers use electronic circuitry to detect PL > tones, and aren't the detectors not using a ringing decoder? If so > isn't the purpose of having a "reverse burst" unnecessary? > I can remember many years ago that some hams used a circuit which > they refered to as "polish PL" which turned off the PL tone before > the xmtr dropped and had no "reverse burst". It seems like I'm > hearing more of the same. > Where am I going wrong here? > Allan Crites
The problem with just turning the tone off is that most all decoders take a MUCH longer time to just coast to a stop, rather then be told 'I'm about to go off the air, close now'. Digital squelch (CDCSS, or DPL in Motorola terms, DCG for GE folks) sends a short burst of 133hz tone for the same purpose-to let the decoder know that the transmission is over and to close. And everything I saw had Motorola's original R/B at 120 degrees, not 270. But as someone wise once said, "I could be wrong." -- Jim Barbour WD8CHL
