Digital voice on HF

I was going to title this post "D-Star's nemesis" but I thought that would be too provocative and premature! But the much talked-about Codec2 open source voice codec has just surfaced in usable form, in the shape of an easy to use bit of software called FreeDV.

FreeDV running on Windows

FreeDV is available for Linux, Windows and Mac. I installed the Windows version, which is just a matter of extracting the files from a zip archive into a folder.

If you're set up to run digital modes on HF then you're half way there already. FreeDV uses the same sound card as your digimode software and the same audio levels. As with PSK31 you just need to make sure you aren't driving the transmitter into ALC.

You'll need a second sound card for the receive and transmit audio. Assuming that you aren't using one sound card for both digimodes and computer sound, this will be the one you use for Windows noises. On my shack PC that's one of those el cheapo eBay USB sound card dongles. You'll also need a microphone or a computer headset.

There's no VOX (perhaps that will come in a later version of FreeDV) so you have to click a button to toggle PTT. Before you can do that you need to set up PTT using a com port. In my case the same serial port used for CAT control and updating the firmware of my K3 was used. The rig went straight into transmit until I ticked the RTS +V check box.

The main challenge is finding other people who are using FreeDV. At the moment the frequency 14.236MHz on 20m seems to be the only calling frequency. It would be nice to have some centres of activity on other bands, but no doubt that will come in due course. There's a Digital Voice Google Group which will probably become the meeting place for FreeDV users.

A FreeDV transmission is 1.1kHz wide, less than half of the bandwidth of an SSB signal. The audio is best described as telephone quality. It's a bit boxy, but there is an equalizer called "Filter" in the software that can be used to brighten up both the transmit and receive audio. A nice feature of the software is a button that lets you instantly switch between analogue and digital so you can easily make comparisons. I wish I could include a clip of the audio recorded off air but I couldn't figure out how to do it.

Right now I'm sitting on 14.236MHz waiting for someone else to come on the frequency. Hopefully as the word gets out more people will get on the air with FreeDV and contacts will be easier to come by.

Icom launches a new handy

Icom ID-51

Icom has demonstrated a prototype of its latest dual-band handheld transceiver - the ID-51A. (The European version will be the ID-51E.)

Covering 2m and 70cm, the ID-51 can also receive FM broadcasts and AM short wave radio. It supports D-Star (of course) as well as FM mode, and boasts a large 128x104 pixels display, the largest yet seen on an amateur radio handheld rig.

Like its smaller sibling the UHF-only ID-31, the ID-51A/E has a built-in GPS which can be used for track logging to a micro-SD card. The storage card can also be used to record incoming and outgoing voice traffic. Very useful - not!

Disappointingly though not unexpectedly, this new Icom does not support APRS, though it presumably supports D-Star's rather lame version, D-PRS.

The ID-51 is being billed as the most technically advanced handheld, though it looks like you will be paying a lot for features - like the GPS and short wave receiver - for which most hams will have little use. I doubt that the large display - never mind the GPS - will do much to extend battery life, though Icom will offer an extended battery pack (at the usual inflated Icom prices no doubt.) However it is nice to see a manufacturer breaking the mould for HT user interfaces which have changed little for the last 20 years.

UHF DVAP Dongle on the way?

Rumour has it that a 70cm version of the DVAP Dongle is on the way. Rumour also suggests that the price will be the same as for the 2m dongle. For those who would like to use Icom's new ID-31 D-Star handie and have no UHF D-Star repeaters in range, the wait may soon be over.

DV Wars in 2012?

In 2012 Yaesu will introduce a range of digital voice radios to the amateur market. They have published a Digital Communications Guide for Amateur Radio Operators that describes their new system and answers some questions about it. Yaesu's offering seems to be compatible with Motorola's professional  digital mobile radio system, which offers hams the possibility of a second source of compatible equipment on the surplus market - not that used professional Motorola radios have ever been cheap. But the Yaesu system will not be compatible with D-Star. No surprise there, then.

I have always believed it was a foolish move for ham radio organizations like our RSGB to allow themselves to be bamboozled by Icom into permitting the creation of a digital network that gave one supplier a monopoly. Repeater groups and their members who have made substantial investments in D-Star technology are not going to want to switch to a different digital mode that makes existing hardware obsolete. On the other hand, D-Star itself is becoming an outmoded technology in digital terms. Hams who have been sitting on the fence looking for an up to date alternative that doesn't involve buying Icom are not going to plump for one system or the other while the future looks like being fragmented into rival factions. It will be like the video war between VHS and Betamax.

I think Yaesu's announcement will kill the already lame duck of D-Star and ensure that analogue FM remains the dominant mode on the amateur VHF bands and up for years to come.

EchoLink or D-Star?

Over the last few days I have been running my EchoLink node #3098 connected into the IRELAND conference server. As I've been feeling a bit tired and lethargic recently it has been a way to pass the time listening to QSOs and making the occasional contact.

Apart from IRELAND there seems to be nowhere else on the EchoLink network where there is enough activity that you can guarantee something to listen to or that someone will reply if you call CQ. I know this is like talking of selling your soul to the Devil but would D-Star, which I have never experienced but which I gather has something called "reflectors", be any better from the point of view of making contacts with hams around the globe using a handheld?

Home-build D-Star radio

Years ago, after I built my Elecraft K2 I had the idea that I would only use home-built radio equipment. However I found that it was no longer possible to buy a kit to build a 2m FM radio. This afternoon I visited a site mentioned by Tim, G4VXE in his latest blog posting and was intrigued to find that a Dutch group is working on a design for a VHF/UHF transceiver kit. Not only that, it is apparently being developed in consultation with Elecraft and is built into an Elecraft EC-1 (K2) enclosure!

The basic kit will be for an analogue FM transceiver with modules for 2m, 70cm and 23cm (it isn't clear to me whether you must choose one of these bands or whether you can fit all of the modules.) But with the addition of another module it can also become a D-Star transceiver!

Now I have never made any secret of my dislike of D-Star, mainly due to the fact that one manufacturer has a monopoly on the provision of radios. But a home-brew D-Star transceiver that doesn't require you to buy anything from Icom and would sit neatly alongside my K2 in a matching enclosure could just be the thing that makes me swallow my objections. Yes, it will still have an AMBE chip containing the proprietary codec. But most of my radios contain chips with proprietary firmware so I don't think that's a good enough reason for continuing to avoid D-Star.

Platform for progress

One of the things at the back of my mind when I was writing that the magic of ham radio wasn't in high technology was the feeling that anyone who got into the hobby out of a mania for high-tech toys was soon likely to be disappointed. I've seen it happen when people who are new to the hobby and don't yet know much about it get an enthusiasm for APRS or Echolink. They get disappointed that the network coverage is patchy or nonexistent compared to cellphone coverage because they don't realize that it depends on hams to provide the infrastructure and where there are few hams - or none interested in these particular aspects of the hobby - there are no repeaters and no gateways.

I've seen the same people criticize the latest VX-8, TH-D72 and Icom D-Star radios as being overpriced and unimpressive. They don't like the geeky "walkie talkie" look or the plain 1990s LCD display. They can't believe that APRS radios don't support predictive text entry like the cheapest mobile has for more than a decade. And why can't they have a colour screen and a scrolling map display?

It's easy to dismiss these criticisms as coming from people who don't understand that ham radio is a specialized niche market and that amateur HTs don't benefit from the economies of scale which allow vastly more R&D to be spent on a smartphone costing a similar amount of money. But then I realized that perhaps the critics had a valid case. Manufacturers of smartphones don't completely reinvent the wheel whenever they release a new model. They just design the hardware. But the hardware is a platform. On it runs a standard OS and various apps, a few of which may be customized to the manufacturer or phone but most of which are generic. Given that software development is one of the most time consuming and expensive parts of any new technology product development, wouldn't that be a huge saving?

Why can't top of the range hand-held radios use a similar hardware architecture to cellphones? Instead of a custom design the radio would be a computer running embedded Linux. The RF side could be SDR or it could use conventional technology - it wouldn't matter, that would simply depend on what is most cost effective and delivers the best battery endurance. But all the control functions, together with transmit and receive audio, would be accessible through an API to software. The user interface would be an app.

Since the radio is a computer the interface would be endlessly customizable and all kinds of things not possible with existing radios could be feasible. Instead of entering local repeater frequencies into memories you could install an app that gets your position from the built-in GPS and shows you the nearest repeaters. One click and you're listening on it.

Instead of a plain LCD display showing distance and bearing your APRS capable radio could show a full map display just like APRSISCE currently provides on Windows smartphones. You wouldn't need packet modem hardware in the radio because packet generation and decoding could be done in software. In fact there would be no such thing as an APRS capable radio. The platform would be the same - if you wanted APRS you would just install the APRS application. If you wanted Echolink you could add the Echolink application. If you wanted D-Star you could buy the D-Star app from Icom. If you wanted to work satellites then I'm sure someone would write an app that would keep track of where the satellites are and even control the radio frequencies taking account of doppler.

You could power this hypothetical next generation radio using cellphone battery packs, which are a lot cheaper than the custom battery packs for traditional ham radios. You could even use standard cellphone accessories.

So why won't this happen? I guess the reason for that is that Yaesu, Icom, Kenwood and the rest don't make cellphones. Their business is making radios that are intended to be as dumb as most of their users. Ham radio is just an offshoot. The market just isn't big enough to justify developing what for them would be a completely different and unique hardware platform. So I guess for the foreseeable future we'll be stuck with our geeky walkie talkies and the cool stuff will all be on cellphones.

Is technology good for ham radio?

Several ham radio blogs have linked to the Wired article Why Ham Radio Endures in a World of Tweets. "What is it about a simple microphone, a transmitter-receiver and the seductive freedom of the open radio spectrum that’s turned a low-tech anachronism into an enduring and deeply engaging global hobby?" the author asks. He goes on to describe the thrill of establishing a direct, person to person long distance contact and exchanging QSL cards, which he contrasts with "a world of taken-for-granted torrents of e-mails, instant messages and Skype video-chats." It's a point of view that QRP enthusiasts and many others will identify with.

In the comments to the article many have been keen to say that ham radio is not low tech, citing "VoIP Radio" and digital techniques as examples. They may be true, but I'm afraid the commenters miss the point. The more high-tech ham radio becomes, the less magic there is. Developments like D-Star are about as far from the concept of a simple transceiver and the freedom of the open radio spectrum as it is possible to get. It isn't simple, it isn't free (since it depends on a network controlled by someone else) and it isn't open. Which is why it is anathema to many of us.

There is a danger that the pursuit of technology could turn ham radio into a poor copy of existing communications networks. Ham radio has endured because it has held on to its traditions involving relatively simple technology that most hams can understand and even build for themselves. If we ever lose sight of that the hobby is as good as dead.

Automatic Voice Relay System

One of the reasons why I have not been an enthusiast of the D-Star system is that it creates a separate class of activity incompatible with existing voice modes just for the dubious benefit (from an amateur point of view) of using digital voice instead of analogue. Using EchoLink, IRLP and APRS we already have a global network that allows one ham to contact another anywhere in the world using ham radio, one that does not require anyone to purchase expensive new equipment from Icom or anyone else. What we have not done is put it together in a way that makes it work seamlessly as a coherent network.

Automatic Voice Relay System (AVRS) is an idea by Bob Bruninga, WB4APR, the inventor of APRS, first published in 2000, to create a system that allows users of EchoLink, IRLP and even D-Star to inter-communicate. APRS provides the location and identification information for the analogue FM EchoLink and IRLP users, something that is already built in to the D-Star system. As is often the case, those who have the great ideas don't always have the skills needed to bring them to fruition, so AVRS remained little more than an idea for ten years.

Now, apparently, a developer has been found who is able and willing to write the software that will enable AVRS version 2 to come into being. You can read more about AVRS here. For seamless one-button operation you will need one of the new generation of APRS-capable radios (Kenwood TM-D710, TH-D72 or Yaesu FTM-350) that are able to QSY to a frequency contained in an APRS packet. Some will argue that if you are going to buy one of those, why not buy a D-Star radio instead? But AVRS capability, being based on APRS, can easily and inexpensively be added to any analogue FM radio. AVRS will not leave analogue FM users out in the cold because their local repeater converted to D-Star, as has happened in some parts of Britain.

One of the interesting aspects of AVRS version 2 is the development of A-Star repeaters. These are analogue FM repeaters with a D-Star gateway that use the D-Star network to link them together. Callsign and location (if known) information is transmitted as a 0.3sec APRS packet burst at the end of each over. A-Star users will appear to D-Star users just like other D-Star users and can easily intercommunicate. A-Star users can initiate a contact with another A-Star or D-Star user just by sending an APRS message starting with A*. A-Star users don't even need to be monitoring a repeater in order to be contactable: they will receive the message as an ordinary APRS message and can QSY to the repeater (with one button press if using one of the radios mentioned above) using the information contained in it.

AVRS looks like a great idea with the potential to bring digital and analogue voice users together. It might even erode some of the analogue vs D-Star conflict.

Open digital voice codec released

David Rowe has released an early version of his low bit rate open source digital voice codec. Whilst this is certainly a significant achievement, I can't get very excited about it for two reasons. First, it is incompatible with the AMBE codec used by Icom in D-Star, so it is never going to be able to work with existing D-Star equipment and it is not all that likely that it will be incorporated in future versions. And second, I still don't see what benefits digital voice offers us as radio hams in the real world.

Digital audio gives you clear "fully quieting" audio up until the signal starts to be lost, when it quickly breaks up and you get nothing. Analogue audio experiences a gradual degradation as the signal gets weaker. Those who have used the two report that an analogue signal is usably copyable about 15 - 20% further out than a digital signal. I can understand that for some professional services nothing but clear copy will do. But we are amateurs who are supposed to be good at digging weak signals out of the noise. Is this really "progress", in the context of what ham radio is used for?

The other reason for my antipathy to digital voice is that I question whether we need another voice mode at a time when VHF analogue voice operation itself seems to be in decline. Surely it would be better to be making more use of existing technologies like Echolink to create more activity for users of existing equipment than to introduce new digital modes that will have an even smaller number of users. I've seen D-Star radios up for sale because the original purchaser found there was hardly anyone to talk to, and D-Star has now been around for several years. I don't see the availability of an open source digital voice codec changing that situation somehow.

Save Analogue FM

Practical Wireless editor Rob Mannion G3XFD has been writing to radio clubs urging members to support a campaign to save analogue radio. However, the radio he wants to save is not ham radio but broadcast FM radio, which has been threatened with closure in the UK forcing users to switch over to the "new" Digital Audio Broadcast (DAB) system.

The much vaunted DAB was supposed to re-invigorate the UK's radio industry, provide a raft of new and interesting IP based services to audiences, permit the launch of new national, regional and local radio stations and generate new marketing revenue for radio stations. However, DAB is almost dead on its feet, as users have been reluctant to buy expensive new radios which in many cases offer poorer reception and fewer stations than they can get on FM. If this reminds you of something more amateur radio related you can probably guess where I am going with this.

D-Star was supposed to re-invigorate VHF radio usage, deliver a raft of new, interesting IP based services like text messaging, DPRS and file transfer to users, permit international, national, regional and local contacts and generate new revenue for Icom. However it is struggling to gain acceptance as people have been reluctant to buy expensive new radios that will provide access to fewer repeaters and fewer local contacts than they can get on FM and have been underwhelmed by the new features offered. Nevertheless the creeping D-Starization of the VHF and UHF bands continues, with the regulatory authorities now apparently refusing to allow new analogue repeater proposals whilst fast tracking D-Star applications through the system.

It does not seem to me to be beyond the bounds of possibility for the powers that be to decide at some point that there will be a ham radio digital switchover, that all analogue repeaters should be switched off and sections of the bands previously authorized for analogue FM use will be allocated to digital.

Perhaps we amateurs need our own campaign to Save Analogue Radio before it is too late. If you oppose the D-Starization of the amateur VHF and UHF bands, feel free to use the "No D-Star" logo on your website, your forum avatar and anywhere else that people might see it.

Threat to APRS, Echolink, D-Star in New Zealand

Steve, GW7AAV, spotted a news item on the NZART web page which states that the authorities in New Zealand have become concerned about IRLP, D-Star, Echolink, APRS and similar modes as they do not appear to fit within the New Zealand license conditions. Their concerns include the use of unattended transmitters and unlicensed digipeaters for APRS and amateurs based overseas operating a NZ amateur station via the internet.

It's easy to forget that other countries don't have such liberal licensing conditions as we do in the UK, although I would point out that operating an Echolink, D-Star, IRLP or packet radio (including APRS) node is not within the standard license conditions here either - you are supposed to apply for special permission. I know there are many who feel that is a good thing, and even that internet linking is not amateur radio and should not be allowed anywhere in the world, at all, but my opinion is that prohibiting it devalues amateur radio.

This policy is probably one of the main reasons why the APRS RF network is broken for messaging as many people (myself included) who are unwilling or unable to comply with the requirements for obtaining permission avoid the problem by operating receive-only gateways. Consequently we have the situation where smartphone-based APRS using mobile internet connections are more useful than APRS over radio.

I certainly believe that the point of our hobby is to use radio wherever possible, but where the internet makes possible something that could not practically be achieved using RF alone I think that we should be permitted to use it.

D-Star's hidden blacklist

The QRZ.com thread resulting from the news about the French petition to have D-Star made legal has not degenerated into the usual flame war. This afternoon it produced this interesting post by Gavin, G0LGB whe makes some observations that are quite jaw-dropping.

Gavin claims that "Repeater groups are being persuaded by financial incentives, free or drastically reduced equipment, fast-track applications via RSGB/Ofcom, to convert their under used repeaters to D-Star." The logic of how converting an under used repeater to use a little-used digital mode will increase traffic escapes me. More likely it has to do with starting to establish a network by the back door in the hope of encouraging more users, after which the busy repeaters will come under pressure to change too. We are having D-Star forced upon us whether we want it or not!

The other worrying claim Gavin makes is that the repeater keeper has the ability to ban users, not just from the repeater but from the D-Star network as a whole. This would be fine if it was simply used to ban miscreants - though why someone would pay £500 for a radio just to swear or play music is also a mystery - but apparently people have been banned just for voicing opinions unpopular with the repeater owners (somewhat reminiscent of my own experience with the ROS digital mode!) This is possible because the system is digital - all packets of audio or data originating from you are stamped with your call so the network knows who you are and where you are (or at least which repeater you are in range of.)

I think that, regardless of the merits or otherwise of using digital voice on the VHF bands, D-Star is not the way to go. It vests too much power in the hands of one manufacturer, Icom, and in individual repeater owners. It's just unacceptable to have a situation that could result in you being barred from your hobby just because a repeater owner disagrees with your views. I suspect that the people who find APRS too much like Big Brother won't like this either.

D-Star illegal in France

Steve, GW7AAV, was quick off the mark to post about the announcement yesterday on the website of DR@F, the French association of amateur digital mode operators, that D-Star has been ruled illegal in France. The reasons for the ruling, if I understand correctly, are that D-Star permits a radio to be connected to the internet (which is apparently illegal in France) and that it breaches rules prohibiting encrypted communications on grounds of national security because parts of the patented proprietary AMBE codec are undisclosed.

The group is appealing for all European amateurs to sign a petition to the European Parliament against the ban. No doubt this will have as much of an effect as the two petitions to the British Parliament to get interference-causing internet-over-mains-wiring devices banned. Issues like this illustrate what a hopeless idea the European Union really is as it attempts to harmonize things between member states while countries (especially France, which started the EU but implemented only the directives that suited it) stick tenaciously to their own different rules and regulations when they want to.

I'm not sure if it is true that French amateurs are not permitted to connect radios to the internet, as if it were, Echolink nodes and APRS gateways would also not be permitted, and a quick check of some relevant websites show several of each with F callsigns currently operating. As for the argument that transmissions are encrypted, whilst the closed and proprietary nature of the codec does prevent someone from designing their own decoder, the chips (and indeed D-Star radios) are readily obtainable allowing anyone who wishes to do so to monitor communications.

I am not, as regular readers know, a fan of D-Star, but this looks to me a bit like the result someone who is also anti D-Star trying to abuse their position to get it made illegal in France. I hope our French comrades are successful in getting this ban lifted.

D-Star reaches Cumbria

Kudos to Lynn KJ4ERJ, developer of the brilliant APRS client APRSISCE. Yesterday he read my comment that the program doesn't support transmit through the soundcard based AGWPE software yet, and today it does! So now my APRS beacons are braaping out over the Cumbrian airwaves.

I have noticed a bit more APRS activity round here in the last few weeks. Today I noticed another new station mobiling around the north-east of the county - G7NZR. The info for this station showed that he was actually using DPRS, the digital version of APRS, and was being gatewayed through MB6CA. This is a D-Star simplex node set up by G7NZR. Its coverage map shows that MB6CA can't be heard in Cockermouth or Workington, so for the time being at least West Cumbria is still a D-Star free zone.

When I looked at the MB6CA coverage map I was reminded of a map I saw some years ago showing the spread of grey squirrels across the county. Overseas readers may not know that the grey squirrel is an illegal immigrant - from the US, no less - and it has been gradually wiping out our indigenous red squirrels, so that there are now only a few pockets of them left.

Will D-Star be the grey squirrel to analogue FM's red, gradually increasing its territory as more and more people are persuaded to make the switch, until Icom ends up with a virtual monopoly over the VHF and UHF bands?

Could D-Star destroy ham radio?

In a comment to an old posting about D-Star in G4VXE's blog, Lee N2LEE accuses me of being closed to new ideas. Does it matter that the AMBE codec is patented if it is the best one for the job, he asks? And how can you compare Echolink/IRLP to D-Star when D-Star is an digital end to end system with routing, linking and networking built in to the system so you can just enter someone's callsign and the network will find them automatically?

To me, ham radio is not and never has been about reliable point to point communication. Communication is just the end-product of a process of experimentation and construction, or a pastime (think contests, DXing) where the unreliability and unpredictability of it is what makes it a challenge.

D-Star's use of a proprietary codec closes that aspect of the system to experimentation. It doesn't even permit interested amateurs to look at the code and see how it works. This is contrary to the spirit of amateur radio and the openness that has facilitated most developments to date by letting one idea lead to another. But to be honest I'm not all that bothered about the issue because codec technology, whether proprietary or not, is a closed book to most. I am more concerned about the possibility that digital voice modes might one day make analogue modes obsolete so that building a simple phone transmitter using SSB, FM or AM becomes a pointless activity. Ham radio does not have to slavishly adopt new technology, especially if that technology forces more of us to become appliance operators by making simple rigs that anyone can build obsolete.

As for digital end to end routing, why do we need it? We already have a system that can do that. It is called the mobile phone network. I didn't get into ham radio in order to be able to do something ordinary people can already do. I want to be able to do things that they can't. The unpredictability of propagation and the uncertainty of who you might work on a given band at any time are what makes a ham radio contact more interesting and more of an accomplishment than making a phone call. D-Star may be very clever technology but what it delivers is not what ham radio is about.

If the time ever comes when I think to myself "why am I struggling to make this contact on 20m SSB or whatever when I could simply type the guy's call into my D-Star radio and have a comfortable chat" then that is the day I will give up the hobby for good. And I make no excuses for resisting the adoption of technologies that will bring that day closer.

EchoLink hotspot update

I just had a reply from the RSGB's ETCC regarding my NoV application. In a nutshell, applying for an NoV to use a 2m frequency for a personal short-range node is a non-starter as "it would be entirely inappropriate for RSGB to assign one of the scarce channels available within the 2M band for your personal use." However it is possible to use provisions already in the license for "remote control of your station" to operate on any frequency I choose, without an NoV. So I have asked them to withdraw my application.

As a holder of a full UK amateur radio license, there are apparently no restrictions on frequency or power that I can use for the remote control circuit (other, of course, than those that apply to normal amateur radio operation.) However the link has to be "adequately secure" to prevent unauthorized transmissions. Typically for a legal document, no specific guidance is given as to what "adequately secure" means from a technical point of view. Limiting the power - or, perhaps more importantly, the receiver sensitivity - so that it cannot receive anything other than my own transmissions might be good enough, but I certainly would not consider it adequate security for my WiFi network (though a few years ago, before everyone got WiFi equipment, I certainly used to.)

Using a transceiver that supports DCS like my FT-817 - as I am currently doing - might be considered acceptable, though it wouldn't take too long for someone to run through all the available codes and find out which one I am using. However I don't want to use the FT-817 for this forever, I'd prefer to find something cheap that I can dedicate to it, and most of the cheap ex-commercial radios don't support things like DCS. They also run too much power. So at the moment I'm not sure what the best long-term solution is.

I hate to admit it, but I can see that D-Star has the advantage here. Being digital, it knows who is calling in to the system. I presume that the DVAP Dongle has a facility to limit access to your own specific call, which would solve the security issue once and for all.

Perhaps I'm worrying too much about this. After all, the reason I'm doing this is because there is very little local VHF FM activity receivable from here. Which means the likelihood of anyone accessing my node, even if it was unsecured, is practically zero.

Postscript: I think I may have found the solution.

Local hotspot

The Digital Voice Access Point (DVAP) Dongle is a small device now available in the US that plugs into a computer and lets you create your own low power (10mW) RF gateway to the D-Star network.

Leaving aside my dislike of D-Star (it is incompatible with existing radios and requires you to purchase an Icom radio to participate, which in my book makes it effectively a proprietary system) for a moment, as someone living in an area where you hardly ever hear any 2m FM activity I can see the attraction of something like this. It would allow one to make some internet-linked ham radio contacts from around the house using a hand-held.

A couple of years ago I started looking into the idea of setting up a low-powered personal EchoLink node, for similar reasons. I prefer EchoLink to D-Star for the simple reason that almost any existing FM radio can use it (as long as it has a DTMF keypad). EchoLink has been going for years and already has a critical mass of users, which is surely more important from the point of view of finding people to talk to than using some new and more state of the art system?

Unfortunately it appeared that in order to set up an EchoLink node I would need to apply for special permission, providing details of three people who could turn the equipment off on instructions from Ofcom, wait months for permission to be granted, etc., etc., which is way too much hassle. I don't think you are exempted from this procedure simply because the RF output power of the node is very low. Because of this restriction doubt if many people in the UK will be using the DVAP Dongle either.