[TrunkCom] Control Frequency Only Mode

Wed Oct 26 21:13:23 EDT 2005

Do youknow if when rebanding happens if they will be changing base
frequencies and other things in older Motorola systems?  I know that with
some systems they may be considered to be splinter systems  in this part
of the band.

On Wed, 26 Oct 2005, Jay Eimer wrote:

> Basically, Motorola uses an "absolute" channel number, and EDACS and LTR use
> a "relative" one.
>
> In Motorola systems, there is a base frequency (something like 850.0000) and
> a "step" (say 0.0125)  Any frequency that could possibly be used can then be
> expressed mathematically as base + (step * channel).  What will break the
> scanners with the rebanding is if they change the base (say to 840.0000).
> The control channel says the same thing (go to 500 translates to go to
> 850.0000 + (500 * 0.0125) or 856.250.  If they change the base to 840, then
> "go to 500" means go to 846.250, and the old scanner still goes to 856,
> instead of 846.
>
> In EDACS, the control channel says "go to SLOT 3" (I used slot intentionally
> to avoid confusion - the computer really does it in binary so the term used
> doesn't matter).  The radio (user's) interprets that as "go to memory 3".
> The scanner handles that by going to "the channel in this bank ending in
> '03'".  So it always works, as long as the right frequency is stored in
> memory x03.  If they change the freqs used by the system, you just reprogram
> the memories to match.  But that's also why the LCN order matters.  If LCN 1
> is 856.0125 and LCN 2 is 857.0125, if you reverse them, you always go to the
> wrong frequency.  The scanner goes where the control channel data told it to
> go - but the call it expected wasn't there.
>
> HTH,
>
> Jay
>
> -----Original Message-----
> From: trunkcom-bounces at mailman.qth.net
> [mailto:trunkcom-bounces at mailman.qth.net] On Behalf Of JERRY NONE
> Sent: Wednesday, October 26, 2005 13:05
> To: Discussion of Monitoring Trunk Radio Systems
> Subject: RE: [TrunkCom] Control Frequency Only Mode
>
> So then why don't we need the L.C.N.s or Channel Numbers for Motorola but we
> need them for EDACS and LTR?
>
> --- bearcat <rwnewbould at comcast.net> wrote:
>
> > Each 800/900 mhz freq has been aasigned a channel no.  The control
> > channel data from the system tells the units which channel no. (hence
> > freq) to go to.  The scanner gets the information from the system
> > control channel so they can add as many new sites as they need and the
> > data will then be on the system control channel so the scanner handles
> > if just fine.  This is why rebanding is such and issue the channel
> > no.s being sent will make no sense to the scanner.  The advantage to
> > using CC only programming is that if something would change on the
> > system the scanner user will never miss a beat.  If you have all of
> > the freqs programmed in a a new site is added you will not hear it.
> >
> > This is explained to the best of my limited tech knowledge
> >
> > Rich
> >
> > -----Original Message-----
> > From: trunkcom-bounces at mailman.qth.net
> > [mailto:trunkcom-bounces at mailman.qth.net] On Behalf Of JERRY NONE
> > Sent: Monday, October 24, 2005 10:58 AM
> > To: Discussion of Monitoring Trunk Radio Systems
> > Subject: Re: [TrunkCom] Control Frequency Only Mode
> >
> >
> > Does anybody have a copy of this band plan?
> >
> > --- Jeff Kenyon <at649 at tcnet.org> wrote:
> >
> > > Hi Jerry, a scanner that doesn't support control only mode will have
> > > the frequencies as reference to go to for a transmission.  In
> > > control channel only mode, the scanner follows the specific band
> > > plan that Motorola has set up for its various bands such as 800 and
> > > 900
> > MHz
> > > trunking so that is
> > > how this is all possible, and with control only
> > mode
> > > you can hear all the
> > > transmission, and any subsequent transmission.
> > >
> > >
> > >
> > >
> > >
> > > On Mon, 24 Oct 2005, JERRY NONE wrote:
> > >
> > > > Question.  Okay, say for instance you have a
> > radio
> > > > scanner that does NOT do Control Frequency Only
> > > Mode.
> > > > So you program in all the frequencies.  So when
> > > the
> > > > Controller tells Talk group 336 to go to a
> > > frequency
> > > > of 868.7125, how does a radio scanner in Control Frequency Only
> > > > Mode know NOT to go that
> > frequency.
> > > > Instead the message is heard on one of the
> > Control Frequencies.
> > > > Also by being in Control Only Mode,
> > > does
> > > > this prevent the radio scanner from hearing all
> > > the
> > > > transmissions?  I mean if the system you are monitoring has seven
> > > > frequencies and then adds
> > > three
> > > > more frequencies to accomodate extra users but
> > the
> > > > Control Frequencies remain @ the same amount,
> > > won't
> > > > that cut off some transmissions?  What happens
> > > then,
> > > > do you just hear the priority transmisions?
> > > >
> > > >
> > >
> >
> ========================================================================
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> > >
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