A talk group is an address that allows all stations to communicate together who are set up on the same talk group, much like how the US Postal Service uses ZIP codes and addresses to route mail.
There are different organizations that are trying to bring uniformity to talk groups so that if you are set up on talk group 3136 anywhere in the world, you will be connected to anyone else who expects 3136 to be the New York statewide talk group as an example.
Some of the organizations tasked with this mission include Brandmeister, DMR-MARC and DMR+.
HVDN is looking to help coordinate and add resiliency for just the Hudson Valley area repeaters.
An important thing to know about a talk group is that it is administered locally and there are certain ranges of talk groups that may have a different use from one area to the next, but the majority of them are the same all over the world now since DMR is the fastest growing and most used digital voice technology globally available to amateur radio operators.
Here are some examples of talk groups:
3100 = United States Nationwide Calling 4400 = United Kingdom National Calling 4800 = Australia Nationwide Calling
4750 = Belgium National Calling
9 =Local discussion on a repeater not routed over the internet.
A complete list of talk groups can be found in various locations and the goal of HVDN is not to provide this, but accuracy of local talk groups of interest in and around the Hudson Valley.
We do however provide a file in our "Generic & Other Code Plugs" section of the HVDN repository
A reflector is different than a talk group in that its function is to allow different DMR networks to talk to each other with some level of uniformity.
Example based on talk group 3100 which traces its origin back to the early days of the DMR-MARC network is that there was no way for other non-Motorola based talk groups to communicate to other networks such as Brandmeister or DMR+. 4639 is a reflector that "bridges" together the Brandmeister and DMR-MARC networks.
A reflector is always based on needing the internet to work. If the internet disappeared which is not likely, so may reflectors.
Here are some reflector examples:
USA Wide TG 3100 = REF 4639
North East US TG 3172 = REF 4642
North East US TG 31092 = REF 4642
Its not perfect, but between talk groups and reflectors there is much more capability compared to other digital voice options such as Yaesu Fusion, and Icom D-Star.
DMR even allows two discussions to take place at the same time on the same frequency based on TDMA technology. No other existing amateur radio equipment has this capability when deployed correctly.
DMR also takes advantage of being an open standard which may excite computer enthusiasts familiar with open source software who may want to get involved with amateur radio and create something interesting.
Reflectors should function to tie in smaller geographic areas into a larger one or perhaps focus on a broad topic like "embedded computing" or "software defined radio" or "camping & hiking"