Coy: Hi-Q active detectors here refer to RC and high Beta transistor networks that were first used in GE Mastr Pro in the last few years of production and then in Mastr II with the versa-tone networks that were laser trimmed Resistor networks and Op Amps mounted on ceramic substrate. They all made Hi-Q circuits that could either generate a CTCSS tone or provide for the detection of a very narrow band of audio frequencies for CTCSS. You are correct in that the original reverse burst was 180 degrees that tried to stop the vibrating of the mechanical reeds. However, even with mechanical reeds 180 degrees was not the best phase reversal, but it was the cheapest to do. When Mastr II was designed it was decided to use the ideal amount of phase reversal of the CTCSS tone, as it was not 180 degrees and this has continued into today. I would invite you to look into any design on tone detection circuit design, you will find that there is no instantaneous off when the tone quits, be it mechanical, solid state RC, phase detector, or other types. Some phase reversal is needed to turn the detector off if you want as fast a response as can be obtained. Fred W5VAY ----- Original Message ----- From: "Coy Hilton" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Friday, October 29, 2004 7:23 PM Subject: [Repeater-Builder] Re: TKR-740 versus TKR-750 (Was: Maggiore's Service)
> > > If I remember correctly, The reason for the reverse phasing came to > be , was to stop the old reeds that used to be used in the CTCSS > decoders, imediately to force the decoders to squelch the receiver > before the squelch noise. (sometimes called squelch crash). I'm not > sure that I understand the meaning of the term "HI-Q solid state > detectors" unless refers to the L C type of tone detectors that were > used origonally to decode DTMF. Now tones are detected by Phase > detectors, some form of FFT in software, or Active filters using > OpAmps. The phase reversal can acheve the same or similar results in > these. > 73 > Coy > > > --- In [email protected], "Fred Seamans" > <[EMAIL PROTECTED]> wrote: > > To Jim & et all: > > Actually there is a reason that Motorola and GE (now M/A-COM ) > used a > > reverse CTCSS tone burst. The Hi-Q solid state tone detectors that > are used > > by these manufactures have a ring down time delay, the same as > trying to > > stop a mechanical reed after removal of the driving tone. The > design of the > > solid state detector dictates the amount of phase shift of the > CTCSS tone > > that is ideal to stop the ring down of the Hi-Q networks. Both > Motorola and > > GE used the amount of phase delay that worked best with their > design. It was > > not to make other brands function poorly. > > Fred > > W5VAY > > ----- Original Message ----- > > From: "Jim B." <[EMAIL PROTECTED]> > > To: <[email protected]> > > Sent: Friday, October 29, 2004 1:45 PM > > Subject: Re: [Repeater-Builder] TKR-740 versus TKR-750 (Was: > Maggiore's > > Service) > > > > > > > > > > Eric Lemmon wrote: > > > > > > > Unfortunately, the TKR-740 receiver cannot properly respond to > > > > a Motorola reverse burst, but that is a deficiency that I can > live > > > > with. (Geez, I wish Ham radios could encode and decode > reverse burst!) > > > > > > > > > > That's actually Motorola's fault. I think they and M/A-Com are > the only > > > ones who use other than a 180 phase shift for revese burst, and > they do > > > it deliberately to make other brands not sound as good on their > systems. > > > -- > > > Jim Barbour > > > WD8CHL > > > > > > > > > > > > > > > > > > > > > Yahoo! Groups Links > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Yahoo! Groups Links > > > > > > > > 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/
