The two "standards" for reverse-burst are switchable in some of the newer radios, such as those that use CPS for programming. Prior to about 10 years ago, Motorola was under the mind-set that you either bought all your radios from them or none of your radios from them, so system inter-operability didn't concern them. If you bought a "Brand X" radio and used it in your Motorola system, they hoped the audible squelch burst would be annoying enough to get you to go with their brand exclusively. Unfortunately this backfired and a lot of customers went totally with "Brand X" instead of "Brand M". Hence, we now have two slightly incompatible standard methods.
Then we have some of the Japanese amateur radios that don't recognize any reverse burst, and always give you a squelch burst on a PL system. The old PL reed encode/decode units used until the mid 1980s, tended to be a lot more forgiving about the phase difference. In fact, the very old encoders from the 1960s used a center-tapped transformer on the PL board, and switched from one phase to the other with the undelayed section of a T/R relay, so the phase was probably 180 degrees back then. It's only the newer radios with microprocessor-based tone decoders that can recognize and enforce the 120 degree shift. DCS (DPL in the Motorola world) got rid of this dual standard by using a 134 Hz turn-off code for about 200 mSec. ALL equipment now plays together a lot better. The only incompatability is with normal vs inverted codes, and this is more a function of the exciter and modulator circuitry that is, by nature, different between various manufacturers. "So endeth the lesson for today, gentlemen." (spoken by Mrs. Whistler, the little old lady in South Africa in the opening scene of Ian Fleming's James Bond 007 in "Diamonds Are Forever") Bob M. ====== --- Nate Duehr <[EMAIL PROTECTED]> wrote: > > On Nov 28, 2007, at 9:37 PM, Glenn Little WB4UIV > wrote: > > > The 1A is an EIA designation. > > > > See > <http://www.personainternet.com/~northscan/dcss.html> > > > > Google is your friend. Searched for CTCSS > Frequency EIA. > > > > 73 > > Glenn > > WB4UIV > > There's also an EIA/TIA specification for the > reverse burst > standards. I don't have access to EIA/TIA standards > (since you > typically have to pay for them) and judging by the > various websites > that allude to it (marketing material), there's > other things in this > spec, it would appear. > > Here's a blurb from a modern Motorola radio's > marketing materials I > found a while back: > > "The industry standard EIA/TIA-603 lists two formats > for CTCSS Reverse > Burst: The format used by Motorola is 120 degree > phase shift for 180 > milliseconds, while the format used by all other > manufacturers as well > as by aftermarket tone equipment makers is 180 > degree phase shift for > 150 milliseconds." > > They go on to explain that in RSS you can switch to > "non-standard" > Reverse Burst on this particular radio. > > Would love to see the full EIA/TIA-603 spec. But > these days when > standards are purchased instead of public > knowledge... oh well. I'm > also surprised the Moto marketing people forgot to > put the "(TM)" > after the words "Reverse Burst". (GRIN) Maybe it > was hiding in the > fine print of the document and I missed it. > > I was more interested in having found a reference to > a real EIA/TIA > specification for the phase shifts and time periods. > Then more > Googling found LOTS of manufacturer's marketing > materials referencing > it, but no copies of the spec sneaking around on > someone's website. > Oh well. > > -- > Nate Duehr, WY0X > [EMAIL PROTECTED] ____________________________________________________________________________________ Never miss a thing. Make Yahoo your home page. http://www.yahoo.com/r/hs
