Voice over IP
Joe Chester M1MWD reflects on the merging of analogue and digital voice over IP in amateur radio.
Amateur radio, like any hobby, is a very diverse range of activities. And people too. And I don’t want to start an argument here, but there is an old story about a village with three amateur radio operators living there. The question is how many amateur radio clubs are there in that village? Yeah, I know, trivial, we’ve all heard it. It’s two if you haven’t come across this aphorism before. Though slightly trivial, it does in a way describe the amateur radio hobby in some respects. Another way to say this is that we have a predilection for division. Pick any topic, ask any question, and the world of amateur radio operators divides instantly in two. “I wouldn’t buy one of those” vs “wonderful bit of kit”, sort of thing. I can think of loads of examples, but you know them all. Which, neatly, brings me to DMR. Or Fusion, or D-STAR, or whatever you want to call digital voice QSOs (see what I mean? – instant division, three different ways to transmit voice as a digital data stream, almost a divide and conquer, or is that too harsh?)
The Smallest Station
This column is about small radio stations. Now a question the answer to which will not divide opinion – what does the world’s smallest amateur radio station look like? The answer is a handheld radio. For example, this from Peter G5AIB, “I’ve had a lot of fun from a £30 Baofeng handheld (GT3TP) 8W, on SOTA, getting contacts over 100 miles away on 2m FM, with a telescopic whip antenna (a £30 add on) screwed in the top” (thanks for your email, Peter). OK so far? But you’ve guessed that I’m not talking only about analogue V/UHF ones, but yes, the digital ones too. Stay with me, for I have a really good example (thanks guys – you know who you are). Mike (not his real name) moved to a nice room in a care home when he was 93 years old. An avid operator down the years (it is rumoured that he was trained by Marconi himself!), he has to leave behind all his amateur radio equipment, unless he just wants it for use as shelf ornaments. The guys in his radio club decided that going into a care home was hard enough, without being asked to give up his hobby of more than 70 years. So, they organised a whip around, bought him a DMR handheld and a hotspot, configured it all for him and set it up on the table in his new room. Through the magic of modern amateur radio, Mike now chats daily to his friends both in the local club, and even all over the world, just by using that handheld radio. The world’s smallest amateur radio station! There are many more stories like this, and about other amateurs with restricted or even no outside antennas (what do you do if you live in a tower block?). Yet I can hear the heckling from the back already, even before this is sent to my Editor – “that’s not amateur radio”. Clearly heard, Sir, but wait, I have more news for you. For there is one other aspect of digital amateur radio in all its flavours that I want to highlight. After this, I will return to the technical discussion – I promise (there is much interesting stuff to discuss!).
Evolution
Once upon a time, we all used telephone wires directly connected to switching exchanges in order to make phone calls. The early ‘exchanges’ were manual plug-in cord types, until Mr Strowger invented a way to do this job mechanically. End of the ‘operator’ – a well-known story. But then someone (actually a disparate group of friends of mine, both here and in the US), invented the packet switched network, the notion that communications traffic could be packaged in addressable pieces, called datagrams, and shipped all over the world using simple computers that used look-up tables. It works like this: ‘is this datagram for me? yes keep it, no ship it on’, sort of thing. The router was born, and with it the internet became a thing. And what happened next? We (yes, a bit me and my friends again) persuaded the telephone companies to digitise all voice calls, and stick that voice data in datagrams. Voice over IP (VoIP) was the new wave, the future of voice communications. No more mechanical Strowger gear, or the legions of technicians needed to maintain that system. (OK there are legions maintaining xDSL modems, and router tables, but that’s another story).
Now, running in parallel with all of this is the history of radio communications. I won’t go into the details, you know it all, anyway. So, we amateur operators arrive today with our HF transceivers, antenna farms, radio rooms, and all the assorted paraphernalia of the broadcast world. But this world too has (very nearly) gone the way of the telephone world. It’s all IP traffic today. Call it digital radio/TV if you like. We are amateur radio operators:
UK AMATEUR RADIO LICENCE Section 2
Terms, conditions and limitations 1. Purpose
1(1) The Licensee shall ensure that the Radio Equipment is only used:
(a) for the purpose of self-training in radio communications, including conducting technical investigations”
Yet when some very smart people (for once not me!) adopt the VoIP protocol to link analogue (and now digital) repeaters into a vast network of accessible radio nodes, some people instantly go “not radio”. Go figure!
This radio network is worldwide – yesterday, as I began writing this piece, I was listening to amateurs in Ohio in the USA and Perth, Australia, talking with a mobile station in Scotland. How fantastic an achievement is that? Amateur radio adapting, as many industries have had to do, to the impact of the internet. The future of amateur radio? If
various industries have been changed utterly by the internet, then why should it not be the case that amateur radio will also be changed. But changed, as in other areas of life, into a world of new possibilities. For if we can technically solve the question of how to get an analogue repeater to generate VoIP data traffic, and send it around the world, then surely there might be other gateways too? And here I make a prediction – if we amateur radio operators, with our technical knowledge and achievements in radio communications, also embrace the opportunities of IP datagrams and the internet world, then who knows where it will lead us. And maybe the computer and internet savvy young people out there might be persuaded that there is some merit in taking the exam, getting a licence, and joining us in the quest for new insights into the world of radio communications.
Let’sTalkTechnology
OK, so much for the philosophical discussion – now let’s talk technology. First point, it doesn’t really matter which version of digital radio you acquire, because there are gateways, and other workarounds, which can convert from one digital mode to the other. With just a brief look around the web pages, I discovered that DMR handhelds were surprisingly cheap (at least compared with other options, such as Fusion or D-STAR). I think you will also find that the choice tends to be influenced by what your radio friends are doing. In my case, I bought an RT3S, direct from Retivis, but there are other sources around, some of them may even be cheaper.
Now comes the fun bit. This radio was designed for the commercial market and not for amateur radio use. So, a bit of work, not much, is needed to get it going. Again, your friend – the one who told you to buy it! – is probably your first call. It was mine! Now
Nigel G4RWI is an award-winning wizard of the technology world, so after a half-hour or so of coaching over the phone, the radio came to life. Technically, the RT3S, in common with all other digital radios, needs what is called a codeplug. This is basically a list of settings, much like (but rather more than – I’ll come to this later) a list of repeaters with their transmit and receive frequencies and tone settings on a V/UHF handheld. The RT3S is both an analogue and a digital handset, so the settings for some of analogue repeaters went into Channel B on it, with the digital settings on Channel A.
First up was a check call on the local repeater – no problem, good audio report. Then a quick digital call to The Wizard using the RT3S – again, no problem, and a good audio report. You need to understand that the digital world is not quite like an analogue repeater. Recall, that this is VoIP. The handset basically takes your spoken sentences, turns this into a digital data stream, and then transmits this to an access point using an FM radio signal. The access point, sometimes also called a gateway, can be a repeater local to you, or it can be what is called a hotspot – basically an internet-connected computer configured to send this data stream to the internet. The Raspberry Pi is popular for this, but any computer, running the right software, will do. The photo, Fig. 1, shows my RT3S connected to a hotspot.
The digital radio world is also organised differently from, say, a local V/UHF repeater. It’s organised in what are called Talk Groups (TGs). These are basically just collections of access points grouped into a single label. Of course, these access points also have a geographic location – which may not be just local. In fact, many TGs have regional, national or even global reach, because the access points, including the analogue repeaters that are configured as access points, are connected to the internet. When you transmit to a TG, your call is transmitted by all the access points in that TG, wherever these are in the world. As an example, take TG23526. This is a group of access points, mostly in the UK, but with a few overseas (there is a lot more detail here, but I’ll save it for a future piece). So, TG 23526 is a set of internet access points, some analogue, some digital. The result is that if I connect my DMR handheld to TG 23526, I can join the conversation there. I can make the connection in several ways – one is to use a V/UHF handheld via an analogue repeater that is also set up to connect to the internet. Or I could use a digital handheld to connect directly to an access point, which is internet-connected. Note that in all cases, the initial connection is over an FM radio channel. There are other ways to do this, of which more later. And you can do this from anywhere in the world. For example, US and Australian amateurs can connect to TG 23526 just as easily as UK amateurs. Finally, as I mentioned earlier, some of the gateways are also capable of mapping between the various flavours of digital radio.
I have created the figure, Fig. 2, to summarise the whole system, from a high-level perspective. This clearly shows how analogue and digital technologies are merged together to create fantastic new opportunities for radio amateurs. Perhaps now you understand how I heard US and Australian stations on my RT3S handheld. And why the guy in the care home can now play radio with the world’s smallest radio station. I will follow this up with a piece about setting up a digital radio. At least, I have notes about what I did and will share them with you. Meantime, I want to figure out how to mount the RT3S safely in the car. For, of course, one of the joys is that this a mobile/portable handset. Time to have fun!