VHF/UHF Digital Voice – a peek into the future

Digital Voice on VHF/UHF is clearly here to stay. Even though the mainstream manufacturers are supporting it (their own version of it), it’s still fairly niche now. It will grow. But what’s it going to look like in the near future?

As things have developed, we have several walled gardens: D-STAR, DMR, P-25, C4FM (Yaesu System Fusion), and a little NXDN. As NW Digital’s John Hays K7VE has said in talks at several ham gatherings, they are “95% the same, and 100% incompatible.” They all rely on the same AMBE vocoder to encode and decode the digital voice, but they all package it differently.

I’ve been living in a bit of an alternate reality, thanks to shooting video at the ARRL/TAPR Digital Communications Conferences and at some of the more esoteric forums at Dayton and other hamfests. In that universe – actually more of a future than a present – we don’t have to choose which closed system we want to buy into. We don’t have to carry three or four handhelds around to cover all the modes, and hope our belt is strong enough to keep our pants up (and guaranteeing a feature spot on HamSexy). We can operate a single radio that can run all the DV modes, along with analog FM.

That radio doesn’t exist today, but it will.

Bruce Perens K6BP and Chris Testa KD2BMH have been working on a radio they eventually calledKatena, an SDR designed for any mode you could stuff into it (FM, SSB, various digital voice modes), but especially a version of FreeDV for VHF/UHF – a little different than the FreeDV used on HF. The radio would use the open source CODEC2 vocoder for FreeDV, and it could also use the AMBE chip (or derived software… Bruce has been looking into getting around AMBE patents) to do the other modes.

You can follow the progress of the Katena (originally called Whitebox – as opposed to black box, because it’s all open source) in various HamRadioNow videos, starting with Chris Testa’s initial presentation at the 2012 DCC in Atlanta. That’s Episode 44, A Practical Handheld SDR, on YouTube at https://youtu.be/YrbmlP1M1AI. I’ll list the string of videos that cover this topic at the end of this post.

Chris and Bruce have laid it all out there, so it’s a little painful to watch their talk at the 2016 Dayton Hamvention® where they admit defeat… temporarily. That’s in the newest episode, #262, at https://youtu.be/ZK_qLSKlqIY. Goodbye Katena, hello Phoenix.

Chris got as far as a 3rd generation prototype. But Chris isn’t an experienced RF engineer, and he discovered what a more seasoned RF guy might have known already, and probably from the same hard lessons. Wideband RF is very hard. As Bruce explains, making an SDR board that can transmit from DC to Daylight is possible (HackRF and others). But that doesn’t make it a transmitter. The RF it generates is dirty – it has harmonics, noise and spurs all over the place. It takes a lot of work, and filters, to clean that up. So making a radio that can transmit from, say 50 to 3000 MHz with reasonable power and good purity is a challenge. Chris’s design wasn’t up to the challenge, and he explains it in the forum.

They aren’t giving up, but they are going back to the drawing board to take advantage of newer technology (and that train isn’t going to slow down anytime soon). Bruce hopes for a prototype by the Orlando HamCation next February, but I wouldn’t hold him to that.

Meanwhile, Wireless Holdings has announced the DV4mobile, and listed some general specs on their web site. It’s pitched as a 20 Watt, 3-band mobile (144, 222 and 440) with FM plus “C4FM, D-Star, DMRplus, dPMR, P25 and NXDN (later via software update).” It will also include and LTE radio for connection to the cell network, and the software to let you keep using the digital modes through their networks the way you use the various dongles now. Wireless Holdings makes their own series of dongles for D-STAR, DMR, P-25 and Fusion, with varying capabilities. Their announcement doesn’t include FreeDV. Their development has been behind closed doors – they haven’t appeared at the DCC or given talks at hamfests.

Another company, Connect Systems, announced a multi-digital mode radio a couple years ago, and keeps pushing back the release date. They’ve been delivering popular FM/DMR radios (monoband, chose VHF or UHF).

So far, none of the big guys – ICOM, Yaesu, Kenwood or Alinco – have shown interest in making a radio that would do “the competition’s” modes. Kenwood, of course, has thrown in with ICOM on D-STAR, at least for one handheld coming out later this year. Alinco, the company that actually produced the firstdigital voice amateur radio (that went nowhere, but they did it), has yet to commit. Chinese companies are jumping on the DMR bandwagon, but none has produced either a D-STAR or Fusion radio.

The FreeDV radio is sort of a wild card. David Rowe VK5DGR, the ham who developed the free, open-source CODEC2, is working on a radio for FreeDV (and FM). He’s calling it the SM-2000. Bruce talks about it a little in the Dayton forum, and David has published some details on his blog, but it hasn’t crossed over to any kind of polished marketing. I found a recent video of David detailing it on YouTube: https://youtu.be/sg08zgiSFG8. It’s a fairly terrible video with bad audio (mic on camera in the back of the room, so full of reverb), but the information is worth the pain.

He begins with a review of the current FreeDV system for HF Digital Voice. The new VHF stuff starts about 5 minutes in. At about 12 minutes you’ll hear the most amazing comparison of FM and DV I’ve ever heard. The FM is too noisy to understand. The DV is solid. It turns the typical FM/DV comparison on its head. The rest is semi-deep technical stuff that hits my limit, but I get the broad strokes (and all the coughs and sneezes of the audience – I think I might catch a cold just from watching).

Bruce Perens has noted that any of the big or little manufacturers could implement FreeDV for free – it’s open source. FlexRadio has incorporated the HF version in their 6000 series. Nobody had expressed interest in the VHF version, yet. It’s pretty new. So David is developing a radio mostly as a demonstration project, but it will be something you can buy. It won’t be your main radio.

If FreeDV VHF catches on, it’ll be somewhat game changing. A bit narrower than D-STAR, it is also TDMA like DMR – it can switch between TX and RX rapidly. DMR uses that to put two ‘voice channels’ on one RF channel. David Rowe talks about building an on channel repeater that needs no duplexer. Paging Frequency Coordinators!

I would love to have a radio that can do all the digital voice modes. I would like to see what FreeDV could do to VHF/UHF operation, though I’m conflicted about the TDMA repeater concept. That could make repeaters so cheap and easy that everyone could do it… and they would! And the bands would be a mess. Part of the reason the frequency coordinators can more or less cap the number of repeaters in bands that are “full” is that repeaters are fairly difficult and expensive to build and maintain. But if David’s radios work well, that’s what’s gonna happen.

Index:

HRN 44 – Practical Handheld SDR, from the DCC https://youtu.be/YrbmlP1M1AI

HRN 149: What’s a Whitebox? https://youtu.be/WF9SK5f0NUM

HRN 193: Digital Voice is Exploding (maybe) (David Rowe interview) https://youtu.be/SmyVEwjhG_k

HRN 194: HT of the Future https://youtu.be/wq29i8gMm8c

HRN 226: K6BP – Open Hardware Challenges https://youtu.be/kE6mrwTCxus

HRN 238: ‘Front Panel’ (for the HT of the Future), from the DCC https://youtu.be/xHaYrDVYPO8

HRN 262: Digital Modes Now and for the Future https://youtu.be/ZK_qLSKlqIY

FreeDV SM2000 Presentation at Gippstech 2016 https://youtu.be/sg08zgiSFG8

Gary Pearce, KN4AQ, is the host of HamRadioNow.tv. If you enjoy this and other HamRadioNow programs, help keep them 'on the air' with a contribution. Contact him at [email protected].

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