Digital Voice in Amateur Radio

Analogue signals are great in that they are simple enough to generate and demodulate, but they suffer in that the signal quality degrades when sent over a noisy radio link. With radio voice systems, this is heard as pops, crackle, hiss etc. and the problem gradually gets worse as signals get weaker. Human ears do a remarkably good job of dealing with noise but it can get tiring when listening for long periods.

Way back in 1948, Claude Shannon proposed that digital coding systems can be designed in such a way that error-free transmission can occur even through a very noisy channel. My first encounter with amateur radio using error-correction was operating AMTOR in forward error correction mode on the HF bands, from the station of G3IUB at the University of Birmingham in the early 1990s. The station consisted of a Trio TS-520S transceiver (yes, valves!) coupled to an AEA PK-232 terminal node controller, with an amber screen serial terminal made by Wyse. It was actually quite impressive to watch the text on the serial terminal edit itself, so that rogue characters got corrected as more data came in over the air.

Although I’ve been a radio amateur for decades all of my voice transmissions have always been carried by analogue radio signals, modulated by various combinations of phase, frequency and amplitude. However, the increase in computing power and falling costs over time have now put digital voice modulation schemes within reach of the radio amateur.

Recently, several competing amateur radio digital voice systems have come into existence. Sadly, they are largely proprietary and do not interoperate. After all, there is just one radio manufacturer behind each closed protocol. This goes against the spirit of amateur radio (which in my mind is the original open-hardware movement) and it shouldn’t be necessary to buy a specific type of transceiver from one specific manufacturer just to operate in a specific mode.

In 2005, the European Telecommunications Standards Institute (ETSI) ratified a specification for a digital voice modulation scheme. This has been adopted by PMR radio manufacturers and is growing in popularity throughout the world as a new PMR radio standard. Although the voice codec used is proprietary, the specification itself is open and so it lends itself to easy investigation by radio amateurs.

So, I have decided to jump on this particular band wagon. As well as the usual PMR manufacturers, there are now a range of Chinese manufacturers producing DMR compatible equipment very cheaply. I managed to source an MD-380 hand-held radio from TYT, with a drop-in charger, two antennas and a hands-free microphone all for less than £100, including delivery to the Isle of Man.

First impressions are that the codec is somewhat brutal. Everyone sounds somewhat robotic, but once you’ve got used to that the audio is very intelligible. Unlike analogue FM, there is no hiss. No background crackle. None of the multi-path ‘flutter’ you get on stations in moving vehicles. A very strong FM signal probably sounds better than DMR but for hand-portable radios strong signals are rare. Listening to perfect audio from DMR in weak fringe areas is much better than struggling to pull a voice out from the noise you’d hear on FM.

You also get other value-added features with the DMR protocol that you don’t get with analogue FM. Each radio has an unique identity, so you can match that up to a user’s call sign and have your radio display the call sign of the person you’re listening to. That’s great if your memory is as bad as mine, and it takes some of the stress out of mobile operating. Also, DMR was designed with repeater infrastructure in mind which means that roaming between coverage areas is seamless, with no need to fiddle with your radio while driving. DMR is also a time-division multiplex system which means that two separate conversations can occur simultaneously in one 12.5 kHz wide radio channel. You can also see the received signal strength from the repeater at the same time as you’re transmitting into it!

Of course being digital, sending data between repeaters via the internet is easy and so a worldwide network of linked repeaters has sprung up. This means that noise-free global communication is now possible from one hand-held transceiver to another. Thanks to the hard work (and deep pockets) of two local amateurs, we have two linked DMR repeaters on the Isle of Man.

 

 

Printing from a Chromebook

Chromebooks are nice machines, but of course they dance to Google’s tune. Google are usually pretty good at adopting open standards but occasionally they think they can do better. There are established protocols for printing over a network, but Google have ignored these entirely by ensuring that all Chromebooks only support Google Cloud Print printers!

To be fair to the mighty G, they do explain how you can leave a PC running with their Google Chrome browser open to make your existing printer available to your Chromebooks but electricity on the Isle of Man is not very cheap, so I don’t want to leave a PC running all day long.

Instead, I’ve deployed a humble Raspberry Pi along with the magic of GNU/Linux and the Google Cloud Print connector for CUPS to achieve the same result without wasting the planet’s resources.

However, efficiently sipping electricity like this won’t help the island to pay off its debts!

What I learned at OggCamp 2015

I attended my first ever OggCamp on the weekend of 31st October / 1st November. Having never been to any kind of ‘unconference’ before, I didn’t know quite what to expect. So here’s a few thoughts on what I learned:

Free culture and free software types are a friendly bunch.

This happened even before I arrived. Half way up Brownlow Hill, I was staring at a map on my phone when a chap walking nearby asked if I was looking for OggCamp. He told me about the previous ones he’d attended, and we walked up to the venue together. (I also learned the advantages of wearing an Ubuntu T-shirt in public!)

I didn’t realise Mars was as small or as cold as it is.

The first talk I listened to was by Gurbir Singh who gave a detailed presentation about space exploration, and likely future missions to Mars. You can see his slides here: http://astrotalkuk.org/2015/10/31/mars-the-new-space-race

Protocols run the world.

Jon Spriggs (who really is a nice guy) was giving the next talk I went to, looking at the various protocols which run our networks. Lots of great info, but the bits which stuck in my head were:

192.0.2.x is the ‘dummy’ subnet – just like example.com is for domain names
DNS resolvers allow for easy MITM attacks, because the first to reply wins
TLS is the correct name for SSL
SQRL (squirrel) is a new one-click authentication for the web

A lot can happen in five minutes.

The next thing I attended was the ‘lightning’ talks event. This is a slot where people present for just five minutes, and can be asked just one question at the end. A great format which led to many diverse things being presented. For me, the one to remember was about using big USB hubs and some software called Multi-Writer to write an .iso (or .img) file to multiple memory cards at once. I can see me needing this if I ever get round to my ‘Raspberry Pi for Dummies’ talk at IoM CodeClub.

Entroware make nice looking machines.

I’d never heard of Entroware until OggCamp, but they sell Linux based desktops, laptops and servers. They had a few on show in the exhibition space at OggCamp. Definitely worth a look if you’re in the market for a new machine. They also sponsored a lot of what was happening at OggCamp, and even stumped up a shiny new laptop as a raffle prize. Great.

HR Deparments suck.

The next talk I went to was by Stuart Coulson who was discussing ‘hacking’ your CV to gain advantage in the job market. Lots of great tips about why CV’s don’t work, and what you can do about it. It was interesting to think of a CV as device to get HR to pass your application on to someone who cares, in just a 20 second window! Also some good advice about separating out ‘personal’ and ‘professional’ accounts on social media, and creating your own ‘brand’ for yourself.

Talking to new people takes me out of my comfort zone.

But each time I do it, I reckon it gets easier. I didn’t know whether to go to the ‘official’ pub (The Constellation) for the Saturday night drinks. Thankfully, I was spurred into action by a tweet from @himayyay and so left the confines of my windowless hotel box to venture into the real world. I managed not to get lost on the way, and also learned that my legs are much longer than Google’s, as their Maps app had overestimated the journey time by about 100% 🙂

I got myself a drink (priorities, right?) and then loitered. People in OggCamp T-shirts around. People with Linux-y T-shirts. I was obviously in the right place. Everyone was engaged in conversations in groups, so…
…I went outside! Thanks to Twitter though, I met up briefly with @himayyay until the call of KFC on an empty stomach took him and his friend away. Still, I’d done it. Gone somewhere strange in the dark and spoken to people. Strengthened by my success, I went back inside all fired up to break into the group conversations…

…and promptly stood against a wall, clutching my pint for protection!

I thought I’d finish it and go back to my hotel, when I was rescued by Gemma and Dick who spotted my unease and asked if I’d like to join them. Thanks guys! Anyway, within seconds I’d identified them as fellow Yorkshire folk and so knew that everything would be OK. Three more drinks and much conversation later, we were finally kicked out of the place.

My hotel was in the opposite direction to the next venue, so I headed back. Bed was calling.

We have to step up on privacy.

On the second day at OggCamp, I went to a panel discussion chaired by Sally Hanford about privacy. I’d clearly missed a talk from the day before which this discussion was following on from. However, online privacy is something I’m very interested in so it was easy for me to follow along and contribute. It seems we still have to solve the problem of making privacy important to people. I guess in reality, it’ll take more breaches like the TalkTalk one, or a change to a more oppresive and authoritarian stance by our governments before people begin to realise the real consequences of a lack of online privacy.

ESP8266 modules are great for building IoT devices

The next talk I went to was by Tim Gibbon who has reverse engineered the RF interface used in a lot of UK gas central heating systems, so that he can switch his boiler on and off remotely. In conjunction with some inexpensive (about £6 per room) sensors and transmitters he’s able to monitor the temperatures in all the parts of his house, see the information live and historically through a web browser and get the system to crank up the heating automatically when it gets cold. All for a fraction of the price of any commercially available solution.

Update: Tim has made his slides available.

Air travel sucks.

My journey home was hard work. I left OggCamp as soon as it finished, and rushed off to the airport to catch a flight. It was delayed. It was delayed again. It was cancelled.

At this point, people ceased being human passengers and became units for a handling agent to process. Queues three hours long with no seats nearby. Lack of information and updates. When you finally get to the front of the queue, you’re told you’ve been booked on to the next flight in the morning. Queue again to find out where you’ll sleep.

Nobody knows. There are hotels nearby, but the handling agent has to use a national agent who is refusing to answer the phone. Hours pass. Still no seats to sit on. Legs tired. At midnight I call it quits and drop £70 on a hotel room across the road.

Four hours later, I’m up and back at the airport ready for my morning flight. There’s a fundamental problem with airport security if you bought your wife bottles of perfume in duty free the night before. Perfume is a liquid. Apparently, airline authorities are scared of liquids and so I now have a problem. I solve it. (I’m resourceful, y’see.)

So, back in departures. I see a delay on the board. Unease. More delay. Oh look – my flight is cancelled. Once again, we’re led like cattle through the arse end of the airport and back land side. Once again we join the queues of doom…

Rebooked onto another flight later in the morning. By this time their printer has died, and so I clutch a handwritten scrap of paper and have to find another desk to check in again. Oh, and I have to get my contraband liquid gifts through security again. This time I own up, and go for the human misery angle. It works. (Well, you can only use a 0-day once, right?)

Third time in the departure lounge. Time passes. Flight gets delayed. This time though, the news of the actual cancellation comes from the Isle of Man airport (via Zak’s excellent app) when I notice that our flight is listed as cancelled on their arrivals board. It was another 30 minutes before they finally owned up and told us in Liverpool, before leading us through the now very familiar tunnels and passages back to the land side world. I suspect the delay before telling us was because they were trying to manage the length of the queue at the handling agent’s desk!

At this point, I’d lost the will to go on. I couldn’t face the whole queue, rebook, queue, check-in, queue, security farce for a fourth time. I got my lovely wife to phone up and book me a seat on the evening boat from Liverpool, and got myself on a bus into town. I managed to kill time for the rest of the day with the help of a pub and some beer. Felt human again.

The boat was slightly delayed, but the reasons were made very clear. Here is a transport company that knows passengers need information. Here is salvation. I settle in for the journey, only to find my Bluetooth headphones have died. I think the triple X-raying they’d had earlier on had cooked them. Bloody airport!

OggCamp is great.

Really, it is. Great people. Well organised. Lots to learn. Lots to see. Lots to do. Huge thanks to everyone who played a part in making it happen. I had a fantastic time! Fingers crossed that OggCamp 2016 will be a thing.

IUK 5 A1 IP Camera

On a recent trip to the UK, I called in to a Lidl store because I know they often have interesting (well, to me anyway) bits of tech for low prices. I picked up this little gem for a shade over thirty quid.

When you consider it contains wifi hardware, a web server, pan & tilt motors, speaker & microphone and of course a camera, then I think that is a fair price. The device also comes with a UK mains adaptor and a high quality Ethernet cable too, so it has everything you need to get started.

The camera copes well with a range of lighting conditions. I’ve tested in bright sunlight, indoors with both fluorescent and tungsten lighting and all gave good quality images. One thing which really surprised me was the low light operation. The camera automatically switches to a ‘high gain’ mode when ambient light falls. I’m not sure if has a separate sensor for this but the results are impressive. You lose some of the colour details, with an essentially monochrome image but the camera is able to see better in low light than my own eyes can! The camera also has some infra-red LEDs fitted which it uses as a floodlight, so you can even see in total darkness. This works much better than I thought it would, with enough illumination to see clearly to about 6 metres from the camera.

There is a down-loadable app for both iOS and Android devices which allows you to watch the stream from the camera, and control the pan & tilt motors easily. You can also receive a live audio stream, and the camera also has a speaker in it, allowing you to talk back too.

There are terminals provided for interfacing with alarm systems, and you can control this output via the web interface too, so you could use it for whatever you liked. Feeding your pets remotely from your smart-phone, and then watching them eat maybe?

The camera’s web server seems reasonably secure. Two levels of authentication are used. One to view, and one to configure. However, I should point out that the passwords are sent in the clear in URL requests which is a bit daft. Don’t use passwords anywhere else and be aware of browsers etc caching URL requests.

The device also has a telnet port, which doesn’t respond to the login credentials used in the web browser, so I’m not sure who it’s for. It’s certainly not a good idea to expose this port to the wider internet!

The software in the camera also does motion-detection and can trigger the alarm connector output on detection, send emails with pictures attached and upload images to an FTP server so it’s quite good for security use.

Provided you can firewall this device carefully, then it makes a good streaming camera for general internet access. At the moment though, I’m confining it to my local LAN until I can learn more about that telnet port…

HP Chromebook 11 Charging Fix

So, the nice HP Chromebook 11 that my wife has seems to have a design fault. If you let the battery run flat, the Chromebook will no longer charge. Symptoms are that there is no charging LED, and no matter how many hours you leave it with the charger plugged in it simply will not charge the battery. It won’t switch on either, so you can’t even use it plugged in style!

Ideally, you’ll want to recharge the thing every time the battery drops to 20% or so to avoid this issue but here’s what to do if you do manage to kill your Chromebook by letting it run flat.

Carefully prise off the coloured panels on the base, to reveal the screws. Open the the thing up and find the battery connector:

chromebook11internal

Now, disconnect this connector and then connect the charger. You’ll see the orange LED light to show that charging is happening. After a few seconds the LED will turn red indicating a problem with the battery. (Unsurprising since we disconnected it.)

Now, with the charger still plugged in reconnect the battery connector. The red LED will turn back to orange, and the Chromebook will start to charge.

Once charging is complete (indicated by the green LED), you can remove the charger, replace the cover, screws and coloured panels and enjoy your Chromebook again.

Just don’t let it run too flat in future!