The Pesky Details on PTT Capability

Much more detail here than most need to know to use the network but if want the gore and background, enjoy the nitty gritty below.

CAPABILITY:  Picture a pyramid and think of a single repeater sitting at the top and 100 repeaters sitting around the base.  Consider coverage to be only in the horizontal plane.  The 1 repeater at the top covers a small area, around the peak of the triangle.  Now down at the bottom is an area very much larger where a hundred repeaters are used to cover this base.  The talkgroup is the vehicle that carries the audio but also signals the c-Bridge (network control center) just how to route connections to only the repeater at the peak or all repeaters at the base to talk to each other and under what conditions.

So back to the repeater sitting at the top.  It may handle special talkgroups such as Local 1 and Local 2.  The 1 and 2 denote which timeslot is used for any particular talkgroup and not simply that they are two different talkgroups.  Which timeslot you are operating is important to know to appreciate the advantages of having two independent voice “channels”, which becomes more apparent later.  A “Local” talkgroup is only routed to this single repeater (normally), while “Worldwide” is routed to every Ham DMR in the world (in theory and concept) for the very widest footprint of coverage, just like the wide area around the base of a pyramid. 

Between these two extremes are the nuts and bolts of Ham DMR.  Only PNW talkgroups will be discussed here in an effort to keep the information on point and try to keep it relatively simple (don’t laugh).  But there is much heavy lifting being done with these talkgroups on the back end and some confusion is common when trying to work with these nuts and bolts, especially so for our newer users coming from the more simple FM repeater world.

One other talkgroup control types exist and they are Master Control Talkgroups.  These MCT’s switch most network talkgroups On or Off on a per repeater basis.  Newly implemented managers will be created using the master control talkgroup structure rather than based on hundreds of hold-off timers/custom programming into a new manager.  It is possible that some hold-offs will supplement the master talkgroups.  This will mean that all control will be in the hands of a user rather than a complex formula of hold-offs.  This will enable creating a new repeater manager in less than an hour instead of many hours and is a huge timesaver for the c-Bridge admins.  In practice, it is suggested that a user who wants to chat on a certain talkgroup simply kerchunk the master off talkgroup, then PTT the main talkgroup on when done.  Local 1 and Local 2 are sorta like MCT’s but with shorter hold off times but will work with the same ability to control all networked talkgroups off for a few minutes, typically 5 minutes.  More on this master control concept in the MCT page.


PURPOSE:  Talkgroups have a purpose and they can be based on geography, task, diagnostics, language, politics (between the c-Bridge groups not Governor Inslee), enabling timers, control and various special purposes other than voice calls.  Most talkgroups are based primarily on geography in some fashion.  States are very common though regions, telephone area codes and postal zip codes are used as well.

Once a purpose is selected, then more criteria is added into the mixing bowl to enable the use of, for example, a statewide talkgroup such as Washington 1. Most important is to which repeaters to route that talkgroup and if that talkgroup is on full time or normally muted or inactive until a user keys up on the talkgroup to enable it.  All this criteria is programmed into the c-Bridge so that every repeater passes the traffic when it should.  The programming is extensive and be a thousand lines of code for a single busy repeater or network of repeaters.

CONTROL:  It is the ability to turn on talkgroup and disconnect other talkgroups to accomplish routing tasks.  This is accomplished actively by the local user for the most part, either actively via MCT or somewhat passively in the background.  The background work can affect the local user but for the most-part, the c-Bridge bows to the local repeater user’s activity, though MCT will override the background settings.

In the old days when FM repeaters had discrete PTT relays, repeater owners did not want kerchunking as it stressed the mechanical contacts.

DMR is different. Kerchunking is a control method and is beneficial. The FCC does not prohibit it’s use.

There are 2 primary tasks that occur when you transmit during a conversation or just briefly with a kerchunk.  The most important task is to turn-off all other talkgroups on the same timeslot that might possibly go active.  These transmissions also starts their hold-off timers.  These hold-off timers are typically set for 3 minutes.  This is sufficiently long so that a conversation is not interrupted or high jacked by another talkgroup coming in from the larger network.  Some higher priority talkgroups have longer hold off timers of 4, 5 and 10 minutes.  For example, Locals are typically set for 5 minute hold-offs.  Some very specific or limited talkgroups might set 1 or 2 hour long hold-off timers.

The other primary task is to enable a talkgroup that is normally muted or not patched to a repeater.  These are called PTT talkgroups and they can be turned on simply by transmitting briefly as is a kerchunk.  One should listen for a moment as the PTT talkgroup may be in use.  Unfortunately, while your PTT action is processed immediately on the local repeater, that actual connection from other users is not made until their active transmission ceases.  You would then hear the other side of that conversation.

Other lesser tasks are occurring during a conversation as 2 or more timers are in play on any conversation, both on your local repeater as well as the other end or ends of a conversation between 2 or more hams.  This is where more complexity is involved so it all gets trickier.  There are 2 basic ways to view the state of your local Talkgroups.

1)  Master Control: The newer IPSC network managers may have special talkgroups that turn all TG’s off by timeslot for 29  minutes or on for 59 minutes.  29 minutes is long enough for most conversations to run without interruption from other talkgroups.  59 minutes is a reasonable listening period to general monitoring.  Older managers may have some or all talkgroups retrofitted as well.  Local 1 and Local 2 will be typical MCT’s though there timers may be shorter than the dedicated MCT’s.

If a user wishes to have a conversation, then kerchunk the MCT Off for TS 1 or TS 2 and then kerchunk back on the talkgroup you wish to use.  When done conversing, simply kerchunk the timeslot back to normal.

Full time talkgroups will be turned back on (default).  PTT talkgroups may or may not be activated depending on the preferences of the repeater owner and/or the IPSC network manager.  The 59/29 timers are default and may be implemented differently as well.  See MCT for more information.

2)  Passive: The local repeater is idle.  This means that all fulltime talkgroups are patched and the first one to go active, grabs the timeslot and you hear that audio.

If the timeslot stays passive, in other works, no local user keys up on any talkgroup on that timeslot, any networked traffic can come in and be heard…it could be 2 or 20 different talkgroups in random fashion.  The local repeater is simply waiting for the first talkgroup to go active during any short or long period of timeslot idle (no active conversation).

If you wish to follow a conversation without the random interruptions of other networked talkgroups, simply kerchunk the desired talkgroup.  That kerchunk will enable at minimum, a 3 minute hold-off timer to disable the normal talkgroups that are carried full time or any PTT talkgroups that happen to still be active.  You should remember all attempts to talk or kerchunk must be done during that brief idle time between transmissions of the active talkers on any talkgroup that you hear. 

This is why we suggest that turnarounds pause 1 to 2 seconds, so that you or anyone else on any repeater anywhere is able to brake into a conversation or kerchunk out of an active talkgroup.  It is important to remember that your kerchunk may not be acted on immediately.  It is quite possible that it may be delayed until a current talker ends their transmission.  The same applies when you kerchunk a PTT talkgroup into the active state, you may miss the balance of of the current talkers transmission before the activation is completed.  Don’t get frustrated by the delays.  This really is just the opposite of HF where quick-keying is the SOP.  Quick keying is counter productive in DMR.  Please be patient when the system is busy.

Believe it or not, this is the simple state, active state has much more going on.

3) Active:  The local repeater is actively in use by a local user (IE: transmitted within the past few minutes, timers are running, certain talkgroups are being held-off, others may be still be active but only one talkgroup on the timeslot should be active ideally.  Sometimes higher priority talkgroups may still be able to barge in on that local users talkgroup.  This is the more complex and  tends to be confusing for new DMR users.

So let’s try some real world examples, beginning with Local 1 since it is as simple a situation as there is on the PNW network.  Local 2 is similar and likely is the best Local talkgroup to use only because this allows timeslot 1, the PNW primary timeslot, to remain open and available for other users on the same repeater.  Local 1 likely is THE highest priority talkgroup on the PNW network.  Local talkgroups are universally used 5 to 1 over the next most active talkgroup (TAC 310) across the USA.

EXAMPLES: 

1)  Local 1 is one of the highest priority talkgroups as DMR hams tend to want to talk to their local friends but networked talkgroups are still important to everyone.

Local 1 generally has a 5 minute hold-off timer in place.  Most talkgroups have only 3 minutes.  This means that when keying up on Local 1, ALL timeslot 1 talkgroups are held off for 5 minutes unless the timer is renewed by the local user transmission either through a kerchunk or more likely, an ongoing Local 1 conversation.  This insures that some long-winded network activity doesn’t pre-empt your conversation.

Once the conversation has ended, the 10 minute timer continues to run, and continues to hold-off all network activity.  In order to override that residual timer, if so desired, simply kerchunk the talkgroup that you want to use or  to “reactivate” (typically PNW-1 or your statewide).  Or do nothing and the default state will return in 10 minutes.

2)  TAC 310 is a popular talkgroup on PNW’s timeslot 2.  Timeslot 2 has lower priority over timeslot 1 though the two timeslots are completely independent of each other.  Ttimeslot 2 has many more talkgroups to contend with though it still works in the same fashion as timeslot 1. 

The bigger difference is that there tends to be much more traffic from the network rather than traffic which is created by local users.  This means nothing more than you are more likely to have a bit less control over the talkgroups and a bit more network traffic taking over local traffic.

Local traffic on a repeater, no matter the talkgroup keeps that timeslot under the control of the local user.  So when talking to your local users or other PNW users on PNW originated talkgroups, the control is more uniform.  The users of PNW tend to be on the same page, meaning all under the same timers and settings, without the randomness of other network traffic barging in.  So timeslot 1 is more efficient and less frustrating since you are not dealing with thousands of other users who may or may not have a better understanding of the talkgroup dynamics.

Most timeslot 2 talkgroups have 3 minute hold-off timers and most are also on PTT.  So until you hit PTT.  So until you enable a talkgroup, it is fairly quiet.  As only one talkgroup may occupy a timeslot at a time, heavy regulation of the talkgroups on timeslot 1 is necessary.  That heavy regulation takes the form of PTT enabling.

So getting back to TAC 310 use, remember that it is a PTT talkgroup and you should keep that 3 minute hold-off timer active or you will likely loose the talkgroup traffic that you may be interested in listening to.  So kerchunk within that 3 minute window or take your chances on ending up listening to another talkgroup that has gone active during that 3 minute window.

There is a confusing wrinkle on PTT talkgroups as many can be on PTT and active at the same time.  That may not make sense based on my earlier statement about only a single talkgroup may be active at a time on the same timeslot, but what can happen is if you have enabled TAC 310, TAC 1, Bridge and 3 others in rapid succession, which turned on all the hold-off timers but ALSO all the PTT turn-on timers.  The PTT turn-on timers all run at the same time but the last kerchunk controls the turn-off timers.  This means if you are a rapid-fire channel changing kerchunker, you could enable many sets of timers…all running simultaneously, which can affect what you really wish to listen to at any particular time.  Just keep in mind, that if you nothing for 10 minutes, everything is likely to return to normal state.  Rapid talkgroup hopping does allow time for responses from users if that is your goal, so slowing down will enable a more positive experience.

MISCELLANEOUS OPERATING THOUGHTS: 

You cannot hurt the system or network when you use it, test with it or try to break it.  But you can get confused on the current state.  We would encourage you to play, experiment, chat with friends and figure it out…or ask questions in the Yahoo Group.

If your repeater or IPSC network uses Local extensively, if possible, use Local 2 as the primary talkgroup.  This allows your timeslot 1 to remain open to your statewide and PNW 1 talkgroups to remain available for use.  If you use Local 1 primarily, then there is little way for other PNW users to contact your users nor can your users chat with other parts of the PNW network.

If nothing else, when done talking on any timeslot 1 talkgroup, especially the popular Local 1, just kerchunk on PNW 1 or your statewide to sorta put things back to normal.  If you don’t, it can be 3 to 5 minutes (typically) before the timeslot goes back to normal or the passive/idle mode.  Until those timers toll, other PNW traffic will be missed.

When you do announce your call on a talkgroup, more especially on PNW 1, consider saying something more than “W7WOW listening”.  If you are testing, say so.  If you are seeking a conversation, say something compelling.  It is likely that many are listening but otherwise occupied with other tasks and may not pick up the HT and respond.  This author will always respond to a request for a test or a confirmation of audio or a direct call if possible, but seldom to someone announcing that they are listening as it tends to interfere with work that that needs two hands and 10 fingers.  Somewhat on point is this article: The Friendly Repeater.

Many users also scan or have RX Groups enabled.  When you make a call, the call may be missed or missed in part.  Keying up and saying something that puts the call and purpose of the call, later in that call, can improve the chances of a response.  It is very helpful when making your call, to state the talkgroup that you are using as this will enable a scanning user to know which talkgroup to respond on.  Seldom is a user looking at the display  as a short car comes in, so unless you state your information clearly, they are less likely to respond..  Something like this announcement rolls these suggestions into this example: “Good morning everyone, this is W7WOW mobile on PNW-1 from Redmond on our way to visit Governor Inslee”.  Over the top, yes…but likely to get a response.

If possible, monitor the PNW c-Bridge Callwatch screen (filters enabled) or log in to the c-Bridge to see a bit more behind the scenes workings.  If you are actively experimenting or in conversation, you can see exactly what is happening on the network.  This includes your signal strength into your repeater, which talkgroups are active, who has been active recently as well as which repeater in the world they used.  Well worth taking a look at Callwatch.

If you use a networked talkgroup, you should have an understanding of the proper use if you read the talkgroup list above.  If you are not sure, ask on PNW 1 or in the Yahoo Group.  A 2-3 minute conversation on a talkgroup that was inappropriate is not catastrophic, so don’t fret if someone dings you for misuse and that should NOT happen on PNW.  Some of the other DMR groups simply are too tightly wound and have short fuses, typically because new users don’t know the rules and it is quite a problem in their little worlds.  If you get some criticism (audio levels are very common), take it in stride, factor it into your next use of that talkgroup and move forward.  Don’t abandon the DMR ship.  It can be a complex sphere and no one person knows it all or has a lock on any particular aspect of DMR.

If you have 2 radios, try listening to all talkgroups on each timeslot.  PNW traffic is likely to be on timeslot 1 while the network traffic is on timeslot 2.  Timeslot 2 is likely to be far busier and you could miss a call or PNW traffic on timeslot 1.  A combination of RX Groups and scan can minimize some of the missed traffic as a scan list can be set to a timeslot 1 talkgroup.  This is a an advanced topic in it’s own right but with the use of Digital Monitor/Promiscuous Mode, RX and Scan is hardly needed for DMR monitoring.

Kerchunking and the FFC – if you are concerned, see Kerchunking

Ask questions on the IO Groups.  Everyone was new at some point in time and there will always be newer hams coming to DMR.  We all should treat them just as well as we had been treated.  Pay it forward, yada yada…and have fun.  DMR is still very cool after our 12 years in DMR.

First Published: September 21, 2021 Last Updated: 9 months ago by Mike – NO7RF

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