Over the last couple of days I've been experimenting with the digital voice setup that I use at home.
Digital Voice technologies have been being explored by radio amateurs since the early 2000s following the introduction of DSTAR from ICOM and System Fusion from Yaesu on equipment specifically for amateur radio use, along with repurposed Digital Mobile Radio, NXDN, and P25 equipment originally designed and sold for the commercial two-way radio market.
While each of these have their own characteristics they share the same aim of making efficient use of radio spectrum while providing high quality audio along with data features such as location reporting and text messaging.
Many parts of the UK are well served by digital repeaters, and I am fortunate to have two within workable range, GB7FE on 70cm and GB7LV on 2m. Both of these are multi-mode with support for DMR, DSTAR and System Fusion. As a new user the learning curve, particularly for DMR, can be a little steep so being able to use existing infrastructure and obtain assistance from other amateurs is helpful.
My first experiences were on DMR using a relatively inexpensive TYT MD-390 handheld, a ruggedized version of the popular MD-380.
More recently, an upgrade of my main shack radio to a Yaseu FT-991a has brought me System Fusion capability.
In addition to the local repeaters, I also have a Raspberry Pi based device with a digital voice modem that acts as a 'hotspot' - a low-powered gateway to various digital voice networks.
For experimentation the hotspot is useful as it gives the amateur total control of what is going on, and visibility into both the RF and network sides of the system.
Up until now I've been using the Pi-Star linux distribution on my hotspot. Pi-Star is a great tool that works almost out of the box with an easy to use web front end, supports
As I wanted to learn more about how the underlying system works and explore some features not yet presented to the user by Pi-Star, I've been working on my own hotspot setup based on the Raspberry Pi OS Lite distribution and the same application software that Pi-Star uses. I'll write a separate post on how I went about that and how I got on.
As mentioned in my post about Digital Voice, the various technologies available all have their quirks and differences along with the many things they have in common.
A common feature between most of these systems is the notion of Talk Groups, to use DMR terminology. In simplex operation or on a standalone repeater system, Talk Groups allow separate groups of radio users to operate on the same frequency or frequency pair without hearing messages from other groups, and without their messages being heard by those other groups.
On an internet-linked repeater system, a Talk Group can made available on different repeaters or gateways anywhere in the world, creating a wide-area virtual channel.
It's common on DMR systems to have a handful of Talk Groups configured on a repeater or gateway, meaning that it will transmit when traffic for that Talk Group arrives from the internet. End radio users can select which talk group they wish to listen to on their radio.
During a recent conversation on OARC's #digital-voice
text chat I noted my experience that Yaesu's System Fusion lacked the ability
to have multiple Talk Groups ('Rooms' in Yaesu's terminology, Reflectors in
general amateur parlance) presented in this way, it only appearing to have the
ability to switch which single Room was available using the Wires-X interface
on the radio, or the "YSF Link Manager" feature in the Pi-Star DV Dashboard.
Jonathan Naylor (G4KLX), developer of MMDVMHost and many amateur radio digital voice tools, interjected that it was in fact possible do this, using DG-IDs.
DG-IDs are, I found, a bit of an underdocumented feature. The operating manual for my FT-991a includes the following description:
By matching the transmit DG-ID number to the uplink DG-ID number set in the DR-2X/XE System Fusion II digital repeater club, you can access the DR-2X/XE digital repeater used in the club. For communication only between transceivers in a group of friends, you can all match the same DG-ID number; then only your friend's voices will be heard.
The latter part of that is fairly understandable, and is similar to how Talk Groups can be used in DMR Simplex operation to separate groups of users, as described earlier. The first part is less clear to me.
A bit of internet searching led me to a description of a linked repeater system making use of the DG-ID system to allow users to choose whether their transmissions would be repeated by the repeater they were communicating with, or by every linked repeater in the group.
I also found discussion of part of the
YSFClients suite that I had not looked
at before - DGIdGateway. This work by Jonathan provides what I would
describe as a routing service between a given DG-ID and various System
Fusion services.
The sample DGIdGatway.ini
offers an insight into what it can do - associating DG-IDs with YSFGateway,
YSFParrot instances, various YSF2XXX bridges, and specific individual
reflectors.
From the example, I set up my own hotspot and radio with these DG-IDs
YSFGatewayYSFParrot- DV Scotland YSF Reflector (Static)
- Online Amateur Radio Club YSF Reflector (Static)
- FreeStar UK YSF Reflector (Dynamic)
- CQ-UK YSF Reflector (Dynamic)
- SDF ARC Talk Group (Static)
- Scotland Chat Talk Group (Static)
With the DG-ID set to 0, my radio operates as I have come to expect and I can either use the Wires-X menu or the Pi-Star DV Dashboard to change Reflectors.
By setting it to 1 through 7, my radio receives messages for the Reflector or Talkgroup selected, ignoring other traffic. The Static entries will always receive traffic from the internet, while the Dynamic ones require an initial local transmission to activate, and will remain active for a few minutes after the last local or internet transmission has been received. FreeStar and CQ-UK can busy at times so I'd prefer not to have them enabled all the time.
Usefully, the Pi-Star DV Dashboard will show DG-IDs associated with transmissions, so it is possible to observe where activity is taking place on DG-IDs other than the one selected on the radio.
DG-IDs 6 and 7 make use of the YSF2DMR bridge software to connect to
talkgroups on the BrandMeister DMR network. It would also be possible to have
additional DG-IDs configured to link to talkgroups on other DMR networks, or
indeed networks for other protocols for which a YSF2XXX bridge is available.
I have a post in the works about how my MMDVM hotspot is configured which will include more detail on how I went about setting up DGIdGateway.