Posts Tagged ‘AMBE’

Digital Voice (DV) – the new FM?

Once upon a time FM swept away AM, but DV is taking its time despite some clear advantages.

I’ve had yet another stunning 5W mobile QSO on 2m this morning on my way to work. Several miles of clear, unbroken chat, without mobile flutter. DV mode delivers good quality voice against a noiseless background. It is sometimes claimed that coverage is roughly extended by 20% due to advantages of this mode, even. I doubt this is entirely true, but an excellent quality of communication is doggedly maintained before ‘falling off’ very quickly. It is quite robust and packed with extras. Ideal for V/UHF and it’s been around for several years.

Even the 2m band-plan in the UK lists all the simplex channels as dual FM/DV. I must admit that I and my friends keep traffic to the UK DV calling frequency (144.6125 MHz) to ensure anyone equipped with DV will hear us and join. If the current FM population heard our carriers on normal working channels, they would be quick to complain about the noise the noise as QRM.

This is what DV sounds like on your FM radio:


DV mode is famous for being the common mode that binds the larger DSTAR system (Digital Smart Technology for Amateur Radio), but excels as a simplex mode too. No analogue mode will embed your callsign for display, report your GPS position, over a low speed data link – all during a normal voice QSO, rounded off with an inoffensive little beep at the end of the over. (Because there is absolutely no background noise, it’s difficult to detect when someone has released their PTT). This is why DV is such a superb candidate to network via DSTAR. This is where radio marries the internet and we are its children.

The new Icom IC-7100 even has people quirkily chatting away on 4m with DV mode, which I gather works very well.

So what is DV mode made from? Well, your voice is encoded digitally using a vocoder optimised for voice communications in the same way your mobile phone does. The device that does this is called the AMBE chip (Advance MultiBand Excitation). Some people moan that this is unfair being a proprietary device, not being open source technology. However an AMBE chip can be freely bought for just a few dollars and uses proven, reliable technology. Inmarsat have been using it for years.

The digitised voice at 3600bps combines with an additional 1200bps (which you can do anything you want with! Think file transfer, photos, messaging etc.) before being modulated. The 3600bps voice data also includes 1200bps FEC (Forward Error Correction), which sends a little extra data in case any gets lost over the air. When bits are lost, the receiver uses this extra data the plug in the gaps. The modulation scheme is GMSK (Gaussian Mode Shift Keying), which is basically a form of phase modulation. You’ll also appreciate that all new modes often save bandwidth as well as improving quality and a DV carrier will happily fit into 12.5kHz channelised plans.



So, what are we waiting for? The manufacturers! The market is caught up in adoption stalemate, with Icom having settled for DV whilst others shun compatibility. But there are also homebrew DV options out there, with modulator/codec boards that will plug into your FM radio (via the packet port or tap into the discriminator) turning your analogue radio into a dual-mode digital delight.
My home DSTAR hotspot. Comprising 2m PMR radio (underneath), GMSK modem (top) and Raspberry Pi computer (bottom).
There are other digital modes out there too, all with different strengths and weaknesses – and they are interesting. But for the sake of everyday commonality and general take-up, I think DV has it.

So is it time to catch up with modern telecommunications techniques and move away from analogue FM? Maybe there’s something in the more ‘tactile’ feel of FM: The waxing and waning, the background hiss, the heterodyne-ing. You seem to know exactly what’s happening and what’s about to happen. So many modes – enjoy the hobby!

Show Notes #090

Introduction:

  • Join us this episode as our intrepid hosts, Richard and Russ (mad posstcatter!), interview John Hays of NorthWest Digital Radio.

Topics:

  • Interview with John Hays (K7VE) from NorthWest Digital Radio.
  • John has been a licensed amateur radio operator for 40 years. His wife and all of his children are hams, too!
  • A couple years ago John gave a presentation at TAPR, and discussed his wish for a reasonably priced radio for digital communications with just a few connections: antenna, power and Ethernet.
  • Bryan Hoyer (now K7UDR) approached John and volunteered to build one. Their collaboration (with Basil Gunn) resulted in NorthWest Digital Radio.
  • Their first product will be the UDR56K-4 Universal Digital Radio, planned for availability in early 2013.
  • John goes on to discuss the features of their digital radio and some of the design decisions the company made.
  • Specifications (subject to change, of course):
    • 25W 70cm Transceiver
    • 4800 to 56Kbps
    • FSK, GMSK, 4FSK
    • Open Source Linux Platform — a full Linux-based web server is built-in. It uses the Debian kernel, running on an ARM processor (faster than a Raspberry Pi).
    • Web Interface over Ethernet
    • 4 USB Host Ports
  • Applications:
  • The radio can be completely controlled through the web interface or the command line.
  • John talks about other potential applications for their radio platform.
  • Keep an eye on the website for more information and to sign up for email announcements.
  • You may also be interested in John’s blog.

Contact Info:

LHS Episode #090: Purple Hays

Here we are at Episode #090, just 10 away from the century mark. Things have been rolling along fairly smoothly, and except for Russ being deathly ill for the last eight days, there’s not even a lot to complain about. In this episode, we have yet another interview. This time it’s with John Hays, K7VE, of Northwest Digital Radio. These guys are producing an entirely new purpose-built radio platform called the UDR56K. This technology promises to be a great advance in the amateur radio arena as well as in the computing arena. It’s a bit of kit that’s going to find a use in almost every radio amateur’s shack. If you want to find out why, please sit down and take a listen to this episode of LHS. We promise you will not be disappointed.

73 de The LHS Guys

LHS Episode #085: David Rowe on Codec2

Please join us for a special episode of Linux in the Ham Shack. In Episode #085, the hosts interview a vibrant and brilliant engineer from Adelaide, South Australia, named David Rowe. He is the mastermind behind the codec2 open voice codec among several other worthy and equally brilliant open source projects. He dabbles in VoIP, hardware, Open Source advocacy, engineering, voice compression, amateur radio and other endeavors far too numerous to name. David Rowe is definitely one of the more special people occupying our planet and our interview with him is nothing short of amazing. Please tune in and have your mind blown. We look forward to the overspray.

73 de The LHS Guys


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