brainwagon "There is much pleasure in useless knowledge." — Bertrand Russell

2Jan/110

Cascode 7 Experimental Receiver

Here is a nice little receiver project which has many features that are similar to the ones I noted as desireable in my post earlier today.

Cascode 7 Experimental Receiver

Noted for future examination.

2Jan/115

A few thoughts on D-Star

Some chatting on the #hamradio IRC channel on irc.freenode.net have made me think about D-Star a bit more, and I thought I'd write them down to see what other people thought.

If you don't know what D-Star is, it's a digital voice and data technology for amateur radio which can currently be found in radios manufactured by Icom. The Wikipedia page will fill in a few additional details. I'm going to presume that you already know a bit about D-Star, so if you don't, go ahead and click the link.

A lot of people have what I consider to be unreasonable criticisms of D-Star. Of course, whether they are unreasonable is actually a matter of perspective, so you might disagree. Bitching about the trademarked name is pretty unreasonable from my perspective. Complaining about the "brick wall" of digital performance (either the message gets through and sounds perfect, or it fails utterly) is something I think of as unreasonable: all modes have tradeoffs. Arguing that P25 might be a better choice is rather silly, because P25 equipment is horrifically expensive compared to D-Star radios. And I especially think that complaining that D-Star radios are expensive is unreasonable (with some caveats below).

The single biggest reason that we should all be cautious about wide adoption of D-Star is that it relies on a patented digital voice codec. This is bad on multiple fronts. First of all, the DV (digital voice) protocol that the D-Star network uses to send voice data has no way to select alternative codecs (there is simply no place in the protocol to specify an alternative). This means that every investment in D-Star radios locks us into a product which is unavailable to amateurs for any other use. We can't legally write a compatible codec to work with voice data on the D-Star network, nor can we substitute a freely available voice codec and carry that traffic on the D-Star network. What we've essentially done is guarantee that we'll be sending $20 or so to the patent holder for every D-Star radio. That doesn't really sound all that crazy, but there are further problems. As a practical matter, if this company (say) went out of business, we'd have no legal recourse to get new equipment which would inter-operate with our existing investment in D-Star (at least until the patent expires). The current patent holder could just flat out decide to not manufacture the chips anymore, and we'd have lost our investment in D-Star radios.

Think it can't happen? What's the average lifespan of a technology company?

But let's suppose that I am being unreasonable. Maybe DVSI (the patent holders) and Icom (the current single source of radios employing D-Star) are good companies that will continue to sell products at reasonable prices. Isn't D-Star a good choice then?

I'd submit the answer is still no, and here's the reason. Since AMBE is currently patented, we are unable to make our own implementations of the digital voice component of D-Star. If we could do that, a whole raft of interesting applications could be created. We could fully integrate D-Star with other VOIP technologies currently in use on amateur radio such as IRLP and Echolink. We could provide free, open source software to send D-Star traffic over the D-Star network, just as we can now for Echolink. We could adapt the technology for links aboard satellites, where the harsh environment may make the chips which currently implement AMBE an unwise choice for use in space.

Our investment in D-Star doesn't provide us with any of that. In fact, investment in D-Star pretty much precludes any of that.

D-Star does have one huge advantage: it is available today at your local radio store. You go down, you plunk down your money and you can get an HT which provides you all the advantages of digital voice. All of my criticisms aside, I haven't really got an alternative. In fact, I don't even know when the alternative will be available.

David Rowe is currently working on an unpatented codec for low rate speech. He thinks he can get a good sounding voice codec running at less than 2400bps, and his early results are promising enough to make me believe him. Surf on over to see what it currently sounds like. Once we have this up and running, I think there will be a whole host of interesting applications that could be developed for digital voice on HF and up. If there is a project that I think needs the help of the amateur radio community, this is it!

The program WinDRM is a program which implements digital voice over HF frequencies (and higher) using COFDM. It uses the LPC-10 codec at 2400bps (which sounds pretty robotic, but is in the public domain) and Speex (which similarly is a bit rough at only 2400bps). It is sadly Windows only, and not open source.

Ditto for FDMDV. Uses LPC-10, and appears to be Windows only, and not open source. It also hasn't been updated in two years.

I think we need an open source digital voice project using Codec2. I think that in the long run, this kind of experimentation is vital to amateur radio, and will provide a greater lasting benefit than saddling ourselves with single source digital voice appliance.

What do you all think?

Filed under: Amateur Radio 5 Comments
2Jan/111

Welcome 2011, with some project ideas…

Hope everyone has had a wonderful holiday. I must admit that my own vacation wasn't productive in the sense of completing projects: I spent far too much time sleeping in, relaxing and playing far too much Epic Mickey on my Wii. But I have also spent some time thinking about the past year and year to come with respect to the kind of fun projects that I like to do.

2010 wasn't actually a banner year for my outside projects. I did a few smallish programming projects (mostly having to do with generating simple sounds). Tom and I managed to loft a camera on a kite once. I simulated some rainbows. I gathered some parts for a high altitude balloon launch. I bought an FPGA board and got it to blink some LEDs, but made relatively little traction on my ultimate goal of implementing a processor. And I did relatively little amateur radio.

So, here's my list of projects that I'd like to see completed in 2011.

A high altitude balloon launch. It seems now that everyone is doing these, but I still would like to do one. I've got an OpenTracker to provide the APRS downlink, and have radios and cameras that could be used. What's really required is for me to dedicate time to the construction and testing of the completed payload, and then start working on getting the necessary helium tank rentals and balloons. This would be a great project to fly in the summer when the cloud cover is minimal. Maybe a 4th of July launch?

Homebrew a radio. I did manage to get closer to finishing some of my kits over the vacation, but I'm increasingly dissatisfied with assembling PC boards as an intellectual activity. For one thing, if you make a mistake, desoldering and replacing components on a PCB is annoying, particularly when the PC board has been optimized for area by packing as many components onto a board as possible. But more than that, the PCB approach means that your design is fixed: modifications aren't there to be explored. Classic fabrication techniques such as "Ugly" or "Manhattan" construction means that you can simply add or change components, and still arrive at RF circuits which perform well.

So, here's my idea: construct a radio (receiver more important than transmitter) as a series of modules constructed with Manhattan style construction on a number of small boards. Concentrate on learning how each part functions and can be tested. Try to use common, inexpensive components. Make the final radio lunchbox size, rather than Altoid size, because that means we'll have extra space to make modifications. Concentrate on improving your test equipment and the testing techniques.

Antennas. I live in one of those places with restrictive CC&Rs. In addition, the terrain of my lot presents some significant challenges. Currently, most of my ham radio operation is antenna limited: without better ability to hear signals, there is little point in beaming out more power. I've been reading a lot about small antennas (transmitting loops, helically wound verticals and short verticals). Develop and test some of these, perhaps using WSPR beacon operations using different antennas as comparisons.

FPGA cpus. I've wanted to learn about FPGA techniques to design a CPU for years. I now have a BASYS2 board from digilentinc, and while I've gotten it to blink some LEDs, I'm quite a long way from making a CPU. I have a feeling this project will linger on for quite some time, but I'm keeping it on the list.

Experiment with the Kinect. Carmen got me a Kinect for Christmas. I have a couple of projects that I want to keep under my hat until I make some progress on them, but it is a gadget with lots of hacking potential.

Meta issues. It dawns on me that part of my problem isn't coming up with project ideas, it's figuring out how to accomplish them. First of all, there are the usual problems of productivity. Balancing work and home life with the requirements of your hobby activities. I'm not always good at that. But I also think also that I spend a great deal of time working in isolation, and seeking out other enthusiasts, collaborators and mentors would significantly enhance my productivity. I'll be working on that in 2011 as well.

If you made it this far, what are your projects that you'd like to see done in 2011? Either scribble them in comments, or make a post on your own blog or whatever and link them in the comments.