[TrunkCom] digital and subaudible

[Brian J Cathcart]

On Sat, 2 Nov 2002 12:53:38 -0800 (PST) JERRY NONE
<thepolishdude@yahoo.com> writes:
> Dude, you mentioned " later models ".  HGow can you
> tell if you got a older or later model.

You already have a "later" model.  The PRO-92 (catalog # 20-522) was the
original, then came the "A" model (20-522A), then the "B" model
(20-522B).  The only difference between the "A" and "B" model is where
they were manufactured (Japan on the "A" model, China on the "B" model),
and I think an EPROM version number.


> Since I have a Pro-92B, please explain to me as to how
> I can set it to use the CONTROL CHANNEL FREQUENCY or
> the SUBAUDIBLE DATA STREAM.  Thanks, man.

This is something I need to clarify - on the PRO-92A/B, you can select
the method only on UHF systems.  For 800-MHz, the control channel method
is the only one available, and for VHF systems, only the sub-audible
method is available.


> The area that I monitor the most, has 11 Motorola Type
> II frequencies.  In some instances, when I am
> listening what happens is that the conversation will
> sometimes stay on the same frequency and I know that
> the Talk Groups are correct because I got them from 
> http://www.policecall.com and Scanning Northeast Ohio.
> I always thought that the purpose of TRUNKING was so
> that the conversation rotates through the frequencies
> as much as possible.

Trunking does that.  What you are talking about is how quickly the
frequency is released for use by someone else.  Motorola systems can be
configured for either "message" or "transmission" trunking.  "Message"
trunking keeps the frequency active (hangtime) to give time for another
unit to repond.  "Transmission" trunking has no hangtime and drops the
channel as soon as the mic is released (this is what EDACS systems use) .
 In all of the systems I've monitored I've never heard a Motorola system
using transmission trunking, so my guess is that it's rarely used.  So,
when you listen to your local Motorola systems, you are going to hear
hangtime after each transmission, but on EDACS systems you are going to
hear the frequency drop immediately after the unit releases their mic.


> By the way, if the CONTROLLER
> instructs the radios what frequency to move to next,
> then what is the sense of having Logic Channel Numbers
> for EDACS systems.  Ain't that kinda redundant?

Not at all.  EDACS controllers send out LCN's instead of frequency
information.  The controller and radios are programmed with what
frequency corresponds to each frequency.  It's actually the same with
Motorola systems which transmit a hex number that corresponds to a
specific frequency.  The difference is that this hex value is the same
for ALL 800-MHz and 900-MHz systems, as opposed to EDACS systems in which
the LCN frequencies can vary from system to system (i.e. in one system,
LCN 1 can be 866.0125 and in another system LCN 1 can be 854.6875,
compared to Motorola 800 systems where hex 06E is always 853.7625 [800]
or 936.3875 [900]).  Motorola VHF/UHF systems are totally different in
that each system is configured individually with a frequency table
calculated based on a starting frequency and spacing, yet are the same in
that they transmit hex numbers which correspond to specific frequencies
within those systems.


> Now here is something interesting.  One EDACS system
> s TEN LOGIC CHANNEL NUMBERS but only uses 9 of them.
> Why NOT use all TEN?

Either the last channel is not active yet, or it is only used when the
system is fully loaded.  Or, it's not used at all in the system.  There
are serveral possibilities.

--

The Scanner Dude
Brian J. Cathcart - KE4PMJ
South Florida Frequency & Trunking Guide - 6th Edition (On CD-ROM too!)