Thoughts on "Dial a talk group" in FreeDMR.
This operates in much the same way as using the DMR+ reflector (TG 4000 -49999). In FreeDMR you can use any talkgroup available on the system. How to "Dial a TG" is here: https://www.freedmr.uk/index.php/linking-to-talk-groups-via-tg9/
Reviewing the basics
Usually a DMR radio is set up (code plug or config file) with channels set up by Frequency, Color Code, TimeSlot, and TalkGroup. Color code is always set to "1" for all use (unless you have a very good reason to differ). Frequency is already understood. That leaves TimeSlot (TS1 or TS2). DMR separates independent signals in time (about 30ms TS1 then 30ms TS2 and so on). A repeater can carry 2 separate QSOs at once. One on TS1 and the other on TS2. Then there are talkgroups (505, 5050, 9 etc) These are simply labels or flags that repeaters and system servers use to direct voice traffic in an orderly way. In rough terms Timeslot is for the RF side of things and Talkgroup is for traffic handling.
For a signal to be heard the radio channel must have the TS & TG the same as the incoming signal. However there are hundreds of TGs available. It is convenient to directly set up the most commonly used TGs in separate channels in the radio. Simply set the radio to (for example), the call channel TG505 and listen or "kerchunk" a user access channel to hear any traffic. Using these options the RF from your radio will be on the TG you chose (eg 505 or 5050)..
Dial a TG
For TGs you do not have set up in your radio there is "Dial a TG". In this mode you are setting up your repeater (or hotspot) to make a connection to a particular TG. However the RF side of things (Radio to repeater or hotspot) is on TG9. Say you wanted to join a net on TG23525 (extended Freestar) you would "Dial a TG" to TG23525. You then talk and listen on TG9. In fact anyone in using the same repeater would hear the net traffic (and you) on TG9 and would be able to also call into that net using TG9. Stations connected anywhere else on the network will not be able to tell the difference. They would see you as using TG23525. Participation locally on TG9 will keep the connection alive. If listening only the connection will drop out after a certain time. The connection can be manually closed by "Dial a TG 4000".
Dial a TG issues
While a "Dial a TG" is set up (on say TG23525) it is important to know that if another station on the same repeater does have TG23525 set as a directly programmed channel they will hear no traffic as the RF traffic is on TG9. If that station makes a call directly on TG23525 they will not be heard by the stations that are still on TG9 but they will be heard by other stations connected to the network in other places. This can become a problem (particularly during a net) as now TG23525 (a User Access) has been activated. Traffic from the network on TG23525 was being transmitted on TG9 by the repeater but TG23525 has also been activated. If it comes out on TG23525 the statons on TG9 miss out. If it comes out on TG9 the station directly using TG23525 will miss out. There is conflict of purpose and chaos ensues. (This chaos will not happen if the Timeslots used by the direct TG and the TG9 are different).
Another issue affected by this is timeouts. It is particularly evident during a net where stations are waiting for their turn to transmit. A transmission on TG9 will not reset the user Access timer on TG23525 or vice versa so even if all local stations had some means of monitoring the other TG as well, they would still have to keep track of what is happening.
As a result of this it would be advisable for operators using a particular repeater to make a decision on what TGs to use directly versus "Dial a TG". If you are on your own hotspot you can use either method to access a particular TG and others on the network will not know the difference. Using both methods at the same time on the same repeater is chaos.
For the newbies or casual users a directly programmed channel is the easiest option for commonly used TGs.
"Dial a TG" uses TG9 into a repeater. A directly programmed channel does not use TG9. TG9 by itself is local to local on the same repeater (does not pass over the network.)
Some interesting TGs you might like to try
23525 Extended Freestar, Cross connects to other systems (23426 in Freestar), Some interesting nets. 50556 ANZEL - Australia New Zealand EchoLink