Thoughts on Digital voice and hotspots

I get asked often from newbies about digital voice modes, so here is a distillation of my thoughts and opinions on hotspots, modes, capabilities and starting points.

Digital voice gets you into a world of internet-connected hotspots and repeaters and you’ll have chats with new friends from around the world just about at all times of the day. Some talkgroups are busier than others naturally as someone’s always talking somewhere at some time of the day. Digital voice can also carry callsign or geolocation info. Some will transmit/receive images and other data.

Usually but not always digital mode stuff and hotspots are on UHF.

I have both a Zumstar and an OpenSpot2 hotspot. I’ve had el-cheapo pi-star off eBay  with mixed results, it was stable once I calibrated it properly. I’ve also had others briefly as I tested them out and moved on. Let’s start with some options to consider and the high points of each for background then I’ll lay out where I’d go as a newbie knowing what I know after 3 years of having various units.

Uses the MMDVM chipset to do the modulation of encoding and conversion to RF back and forth. Sometimes has two antennas ie. two radios but usually one. Requires Raspberry Pi 3 or better to run. You don’t need to be a RPi genious to use it as all configuration is done via the web. For newbies to this world I suggest getting one that is preconfigured if only to save you hours of learning to install and set it up. Takes a couple of hours to get up and running out of the box if not preconfigured. Can be bought as a kit. Stable once it’s running, mine’s been up for months now without intervention. Community-developed software meaning many eyes are upon it for bugfixes. Entry-level web interface and highly configurable which can also be seen as overwhelming to some folks. Also the most confusing of the bunch, MMDVM-based hotspots are made commercially by ZumSpot (the best one of the bunch) and a whack of folks outta China (super-spot, jumbo-spot, etc). If you go this route stick to ZumSpot for stability and quality.

Original flavours OS1 and OS2, current is OS3. An OS1 will get you going nicely but lacks WiFi so must be hardwired to your home network whereas the 2 and 3 add features people were requesting. SUPER-easy to configure and set up, I had my OS2 up in 15 minutes out of the box. Commercial product with excellent support. Ships from the Baltic region I think.

Roll Your Own:
Find the MMDVM chipset and some software and some commercial digital radio and roll your own. Usually the approach for those who don’t want to buy a commercial repeater to save money.

All will work on one mode at a time (DMR, D-star, YSF) at a time on one frequency. Some will work on two frequencies at once. Some will work different modes on two frequencies at once. Very few do both VHF and UHF however. Some will cross-mode on the device, read this part carefully in the specs — it’s easy to cross-mode between DMR and YSF as the encoding schemes are very similar but much harder to go between D-star and the other two. From the OpenSpot website this explanation “Note that … D-STAR uses an older, incompatible voice codec, and it requires built-in audio transcoding hardware, which only the openSPOT3 has.” Summary – – many of them do all the modes but few of them work cross-mode.

Costs in USD:
Pi-star the cheapest of the bunch as little as $75 off eBay via China but requires the most level of knowledge to operate. OpenSpot are at the high end of the scale new about $305 USD. In the middle is the ZumSpot sold by HRO as a kit at about $175 including the case. Used Zumspots still get $120 on QRZ and used OpenSpot2 about $200 on QRZ.

Now to the radios and programming. DMR is the hardest of the bunch to set up followed by D-star and YSF (aka Yaesu System Fusion aka C4FM). Rephrased D-star and YSF are relatively easy, DMR quite challenging. There are some capability differences between the modes that are largely insignificant if you just want to enjoy voice conversations with others.

Hotspot Choices, knowing what I now know:
OpenSpot – easy to set up, does cross-modes, easy to use interface without much goofing around. Used OS3 don’t come up often. Use the cross-mode capability to get you into all the modes from your D-star radio. Easiest but most expensive approach.
Pi-Star – ZumSpot via HRO (don’t forget the case) but will require some effort on your part to get up of the ground. A little less easy but less expensive than the prior choice.
Generic Pi-Star – requires real effort to get off the ground and set frequency offset (ie. calibration) unless you buy one preconfigured off QRZ. Least expensive but most convoluted choice.

Buy once cry once and get a used OpenSpot2 or a new OpenSpot3 if your radio is D-Star.


Note – I haven’t even touched upon internet servers that do the cross-mode for you via reflectors. That’s a whole other topic for another time.

January 2021 – 73