I have changed the subject of this thread, since it now has nothing to
do with TKR repeaters.
TIA/EIA-603-B, the international standard of the Land Mobile Radio
industry, defines two STANDARD formats for CTCSS Reverse Burst: 1) A
shift of 180 degrees for 150 milliseconds; and 2) A shift of 120 degrees
for 180 milliseconds. It happens that Motorola embraces the 120 degree
(same as 240 degree) shift, while almost all other manufacturers use the
180 degree shift. Motorola adopted the 120 degree shift because they
found that it stopped the vibrating reed of a Vibrasponder module in
less time than a 180 degree shift. While I intuitively feel that a 180
degree shift would be more effective than a 120 degree shift, I am not
going to start a debate on the pros and cons of one shift over the
other. I reported as a fact that there are TWO formats, and that is not
open to debate.
Now that the decoding of CTCSS reverse burst is done within a DSP audio
processing chip instead of a mechanical reed, in almost all modern
radios, the manufacturers can fine-tune the timing and phase detection
circuits so that they can discriminate between a 180 degree shift and a
120 degree shift. I have already experienced the incompatibility
between Kenwood and Motorola reverse burst formats. My solution was to
convert the entire fleet to CDCSS, since there is only ONE format for
digital coded squelch, and I can mix Kenwood with Motorola radios and
have them encode and decode CDCSS in harmony.
The practical consequence of this CTCSS Reverse Burst incompatibility is
that modern Motorola radio systems will not mute silently with Kenwood
and other brands, and vice versa. While it may be argued that the top
LMR brands are using this incompatibility as a marketing tool, I think
it is unfortunate that there is no move to have but one reverse burst
format.
One of the reasons I bought a Motorola HT1250 UHF radio for my
public-safety work is that it is one of the very few radios, and perhaps
the only one, that can be programmed for either of the two reverse-burst
formats, on a per-channel basis. The Advanced tab of the Conventional
Personality page has a box labeled "Non-Standard Reverse Burst." If
this box is unchecked- its default condition- that channel will encode
and decode CTCSS reverse burst in the Motorola format. However, if this
box is checked, that channel will encode and decode CTCSS reverse burst
in the Kenwood and rest-of-the-world format. This is a boon for anyone
who uses more than one repeater system! I have one radio that can mute
silently when talking through the Motorola repeater used by the County,
and also mute silently when talking through the Kenwood repeater used by
the City. To the best of my knowledge, this capability is only
available on the portable and mobile radios in the Professional series.
I expect Kenwood to follow suit in the near future!
73, Eric Lemmon WB6FLY
Fred Seamans wrote:
>
> 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: <Repeater-Builder@yahoogroups.com>
> 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 Repeater-Builder@yahoogroups.com, "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: <Repeater-Builder@yahoogroups.com>
> > > 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
>
>
>
>
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