Talkgroup control or PTT is sometimes a difficult
concept to understand. This page should explain the process so that a
DCI repeater user is able to become familiar with the PTT technique as well as
to be able
to effectively harness the power of PTT.
PTT can enable or disable the linking of talkgroups
based a on a brief transmission or kerchunk on a particular
talkgroup of interest. Normally a PTT enables that
talkgroup active on the timeslot but more importantly, it
disables the other talkgroups that could go active on the
network side. This provides a local repeater user with
"exclusive" use of the timeslot for some short period of
time without concern of another talkgroup high jacking an
active local conversation. PTT works both on full time
or part time talkgroup.
That is it and little more. But that
"little more" part can actually accomplish quite a lot and
that is the crux of the benefit as well as the source of
some frustration. What this page will provide the
reader, hopefully, is more clarity or a better
understanding, on what really is happening under the covers
of the DCI c-Bridge. The Bottom
Master Control Talkgroups
These talkgroups are special purpose and
carry no voice traffic. They will
override the conventional "timer" based programming discussed below.
Newly created c-Bridge managers (IPSC network repeater
groups) will be based on this Master Control Talkgroup (MCT)
concept while older managers will keep their hold-off timers
as the primary method of talkgroup manipulation. Some
managers may have some combination of the two methods
implemented for the full time talkgroups to further enhance
the repeater user's experience. Local 1 and Local 2
can also be used to supplement MCT Off's with shorter but
automatic hold-off timers typically with 10 minute off
More info on MCT's
and how to code and use them. The rest of this page
discusses the more common method to control talkgroups on
DCI and many other c-Bridges.
Ground Rules and Assumptions
for Hold-off Timer based Talkgroups
TRBO allows only a
single talkgroup to be active on a timeslot at any one
time on any one IPSC network or repeater. There is
no audio "mixing" as in analog remote bases/repeaters.
This means there is only a single voice channel at a
time on each timeslot is permitted.
TRBO can support many
talkgroups for use on a timeslot but only one will pass
and that is first-come, first served.
Let's begin with 3
Talkgroups in our example. Let's call them Bridge
2, Comm 2 and TAC 310-2. Interestingly, these are
real life examples on DCI. (Example
In the following example;
and Comm 2 are full-time talkgroups on timeslot 2
and "always on", by
TAC 310-2 is
normally off (unlinked) but enabled part-time via PTT; activated
for 15 minutes
If you hit the pickle
(quick PTT) on TAC 310-2, then TAC 310-2 goes active, is
linked or turned on. An "on timer" begins to run,
typically for 15 minutes of listen time. At the
end of the 15 minutes of listening, the TG is turned
back off. If you PTT at any time during the 15
minutes, the timer is renewed for another 15 minute
So if you are in an active conversation, the TG stays on
or is linked continuously.
However, another control
is embedded in that same PTT on TAC 310-2. It is
almost as important as the turning on of TAC 310-2.
TAC 310-2 has unlinking controls for the other 2 TG's
in this example, Bridge 2 and Comm 2. Every time
you PTT on Midwest 2, you turn off Bridge 2
and Comm 2 for a short period, typically 3 minutes.
As long as you are
actively talking on TAC 310-2, the off timer renews the
minutes of off time on Bridge 2 and Comm 2.
The reason this is important is that only 1 TG may be
actively passed into and out of your repeater on
timeslot 2. If
Bridge 2 and Comm 2 were not unlinked for this short 3
minute period, then your conversation on TAC 310-2 could
be preempted by Bridge 2 or Comm 2. That would be frustrating
for a user in a QSO to have that potential of other TG's going
active and hijacking their active QSO.
So remember, a PTT
typically turns on one TG for 15 minutes while turning off other
TG's for 3 minutes to reduce these potential
preemptions. This is the typical functioning of a
part time or PTT TG control cycle. And it applies
to most of the talkgroups that may appear on a timeslot,
which could be far more than used in this simple
Not all c-Bridge
administrators bother with the hold-off timers as it can
involve adding hundreds of timers but DCI does do this
for all TG's in most cases, or full-time TG's in most
cases, though occasionally no hold-off timers as noted
in the talkgroup matrix.
Once you PTT on
TAC 310-2 and you choose to listen, you will now be
monitoring TAC 310-2 for 15 minutes and Bridge 2 and Comm 2 go off for
3 minutes. You now will be
monitoring all 3 talkgroups for the rest of the 15
minutes or what is now really the last 12 minutes
(tolling of the 3 min HO's).
Whichever goes active first will pass to your repeater.
The others, if they also go active will pop up after the
one before it goes silent...and on and on.
If no one on your
local repeater keys up on any timeslot 2 talkgroups, then these
3 talkgroups will have an equal opportunity to go
active, whichever one is first to capture the timeslot and
only that one TG will be repeated. Very simple and
this is how most c-Bridge tend to handle multiple TG's
on the same timeslot. This is the basic set-up on
most c-Bridges and their repeater networks.
If you wish to turn
off an active talkgroup that is currently being used
elsewhere on a different network, you can simply PTT on
a talkgroup of your choice. This is typically done
when you want to make a call on a different talkgroup.
For examaple, you hear traffic on TAC 310-2 but you now wish to
use Comm 2, simply PTT on Comm 2 while there is a
transition between talkers on TAC 310-2. This can
be tricky if the talkers are quick keyers as you are
likely to get bonked. Short Group Call Hang Timers
programmed at the repeater level helps facilitate this
break-in capability (not all repeaters have short GCHP
While you must catch
a narrow window between talkers, you must also wait for
the Group Call Hang Timer to toll. MotoTRBO default
time is 3 seconds. All DCI repeater owners/admins
are instructed to to use 1 second for their repeater's Group Call
Hang Timer. Some do not and that makes it more
difficult to break in and you may need to wait for a
longer opening or for the conversation to run it's
course. If urgent you could break in on the
conversation and ask the current talkers to pause for 5
seconds or so and then you can PTT on your quest for Comm 2. This is a worst case scenario, but still
The "on" and "off"
timers ONLY affect talkgroups on the same timeslot.
As the bulk of the DCI talkgroups are on timeslot 2, PTT is
aggressively implemented. Timeslot 1 talkgroups
are higher priority and so there are fewer on timeslot
1. PTT use on timeslot 1 are more for priority
control rather than timeslot 2's "first-come, first
If you channel hop
and use PTT, then remember you are turning off multiple
TG's for typically, 3 minutes. Any activity that may have
been active elsewhere will be held off for that 3
minutes unless you PTT your current talkgroup upon your
arrival. This will turn on that talkgroup
immediately rather then waiting for the 3 minute timers
to turn all the TG's back on. You will then you will miss little traffic
and be back to a "known state".
If you are not sure
if a talkgroup is on or off, part-time or full-time,
then hit the pickle to insure that it's on.
The PTT control is
implemented at the end of a current active network users
talk cycle. While you can PTT to enable the "on
timer", it wont become "linked" until the the current
active talker stops his transmission.
The 3 minute timers
were chosen as best average to minimize the
loss of an active talkgroup (frustrating for the active
user) but also not keep the other talkgroups unlinked
longer than necessary (missing other traffic
Some talkgroups have
different timer periods, both on and off timers for
special purposes but unless you know otherwise the
the 15 minute On and 3 minute Off timers to be the
default on DCI.
The repeater owner or
administrator has been instructed to set their repeaters
for a 1 second "Group Call Hang Timer". This is
important. The 3 second default time will
generally be too long to PTT in except for the most
courteous of users. Long time HF'ers tend to be an
issue as quick keying is so common in HF operation.
Transmit Interrupt (TXI)
is strongly encouraged on the DCI networks. It
enables you to be able to de-key an active talker as
well as enabling your radio to also be de-keyed.
This will further enable smoother operation when making
use of PTT. It is not embraced by most other
groups and users seldom even bother implementing the
program it into all of your DCI
channels if your radio supports TXI.
Only the local
repeater PTT traffic controls the status of off-network
non-local repeater traffic on the local repeater.
If there is no local PTT traffic, then the incoming
network traffic is allowed in on a first come (to the
timeslot) first served (to you) basis.
15 minute "On Timers"
and and 3 minute "Off Timers" are typical on DCI but
many other values can be used and that is based on their
specific purpose and beyond the scope of this page.
It is important to
remember that PTT only controls other talkgroups and
links outside of your local repeater or IPSC network.
In other words, PTT has no direct affect on what is
transmitted over your local repeater/IPSC network.
PTT will control what goes out from your local repeater/IPSC
network or what comes into your local repeater/IPSC
network. But everything you do locally always
affects the local repeater and network because it is
connected before the c-bridge has access and therefore,
the ability to control. But once
your PTT reaches the c-Bridge, your
PTT can change everything going out from there or
downstream of your local repeater or IPSC network.
Your local repeater should have its
"Group Call Hang Timer" set for 1 second (not the 3 second
default) for PTT talkgroup control to work best. For
example, the "Bridge 2" talkgroup is active but you wish to use
Net 2"; wait for the transmission to stop, wait for
second "Group Call Hang Timer" to toll, key up on "Local 2",
if you get talk permit tones, you have un-linked "Bridge 2"
(as well as several other networked talkgroups that are also
on the same timeslot 2). The 3 (actually DCI
enables 5 minutes for Local 1 or Local 2) minute activity window renews with every
PTT on "Local Net 2" and will continue to keep all
talkgroups on timeslot 2, off so that you will not loose
the use of Local Net 2. If your repeater owner has not
changed the "Group Call Activity Hang Timer" to 1 second, then it is very
hard to break in between and you may need to wait for the
conversation to clear or a long pause.
This page has shown a
very simple (honest, it is a simple) example of PTT control. Many variations
and more complexity can be added into the controls including
additional talkgroups, the weekly scheduler for talkgroup
and receive only talkgroups. If you understand this 3
talkgroup inter-relationship of control, then even with
additional complexity, the basic control principals do not
operates somewhat differently in that both sides must hit
PTT before a connection is created and that is why it is a
considered a destination talkgroup and should be prearranged. This is
much like a telephone party line where anyone can join in on
the connection, but typically, only the 2 parties are active
in the conversation. Still, it is also a good example
(below) as to how a PTT style talkgroup can coexist with 2
full time talkgroups on the same timeslot. Then just
add 20 more possible TG's on timeslot 2 and you can
appreciate more how DCI manages many talkgroups on 2
timeslots with, arguably, some finesse.
Example Table: This table shows the active talkers affect
on the other 2 talkgroups. Bridge 2 and Comm 2 are on full time
normally while TAC 310-2 is off unless it's 15 minute on timer has been
activated via a PTT.
Comm 2 off
||Turns off Comm 2
and TAC 310-2 for 3 minutes for each PTT
Turns off TAC 310-2 and Bridge 2
for 3 minutes for each PTT
TAC 310-2 (ptt)
Comm 2 off
||TAC 310 now on
for 15 minutes unless key up on B 2 or C 2
Every time a PTT of
TAC 310-2 is done on the local repeater, Bridge 2 and Comm 2 are held off for another
3 minutes. This
provides essentially a clear timeslot for the "active"
use of TAC 310-2 without interruption by Bridge 2 and Comm 2 traffic.
TAC 310-2 will remain on for 13
more minutes after the last local traffic ceases
allowing the "passive" use (listening to) of Midwest 2.
So even a PTT talkgroup is able to coexist with
full-time talkgroups with a minimum of user frustration.
This approach enables many more talkgroups to coexist as
well on the same timeslot.
Congratulations if you have read
If your remember nothing else
about talkgroup controls, then remember to simply switch to
your talkgroup of choice, hit PTT to trigger that
talkgroup active and you
will then know you are listening to that talkgroup for 15 minutes minimum.
If you don't hear anything then announce your
presence in a way that will
compel a response
and remember to say which TG you you are calling on
as many users scan multiple talkgroups and may not
see the active talkgroup on their displays.
TRBO hams are like FM'ers, tend to listen but
not necessarily respond to a
kerchunk or simply to
a tossing out your call. Sometimes you may
need to say that "the sky is falling" or that you
just won the "Publisher's Clearinghouse $7,000
a Week for Life promotion" and does
anyone out there want some of your winnings.
CLOSING THOUGHTS: Some may feel that
this PTT approach is needlessly complicating HAM DMR.
Others may feel that having only 2 or 3 talkgroups
active 7/24 is
a complete experience. DCI's approach is to try to
provide to each repeater owner or repeater manager an
individual or custom set of talkgroups that fit the mold
of the repeater owner or their group of repeaters.
No "one size fits all" is mandated. It is up to
the repeater owners or IPSC network admins to decide if they want 2, 15 or over
60 talkgroups that are available on the DCI c-Bridge.
Assuming one has a good understanding of
MCT, PTT, On/Off
timers and the scheduling of talkgroups, then good
choices can be made so that the repeater owner can
provide the best services for his users.