Category Archives: Amateur Radio

Ring Oscillator Das Blinkenlights

Crap, the original entry I made for this got screwed up somehow. Oh well.

Alan, VK2ZAY, was experimenting with ring oscillators, which make some very nice blinking light displays indeed.

YouTube – Ring Oscillator Das Blinkenlights



Before this post got mangled, I was experimenting with putting the circuit into LTSpice and analyzing it. My brain was too enfeebled to figure out the relationship that governed the selection of the values for the bias and current limiting resistors and the capacitors, so I figured I’d just code it up. Of course, now that this post is mangled, I’ll have to redo the LTSpice analysis, but what I discovered was that under some conditions, LTSpice predicted very long start times for the ring oscillator, or it simply failed to initialize. This is because I typed exactly the same value for the components. If I varied the value of the components by just 0.1%, the oscillator had no problem firing up.

I’ll redo the schematic and the graphs tomorrow. Stay tuned.

Addendum: Couldn’t wait. Redid the simulation using the values that Alan thoughtfully provided on twitter. Here’s the screen dump: commentary to follow at a later date.

LTSpice simulation of a ring oscillator

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?

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.

It receives!

Well, I found a BNC connector, hooked up my antenna, and voila! Before testing it, I tried listening up on my FT-817, and the band seemed pretty dead. But the DC40B had signals!

First powerup of my DC40B

I can hear a bit of hum, which I suspect will only get better once I use a better power supply (I was just using a wall wart) and get it in its case, and its wide, but you can definitely hear signals. At the end, some QRM comes in and spoils it, but I’m encouraged.

Addendum: My morse is pretty rusty, but the loudest signal at the beginning of the recording is a QSO between K6LQ and W6JHQ. W6JHQ would appear to be about 360 miles away, just west of Victorville.

DC40B, Day 4 + over a year…

Back in October of last year, I was eagerly putting together one of Doug Hendrick’s DC40b kits, a nifty little transceiver, complete with a nice metal case. Here’s where the assembly got to prior to today:

brainwagon » Blog Archive » DC40B, Day 4, and stupidity on my part….

Yes, I didn’t install a chip backwards, I merely screwed up and swapped the op-amp (8 pins) and the Atmel chip (similarly 8 pins). At the time, I sent an email to Doug and he kindly sent me replacement parts, and they sat in my “box o’ radio stuff” for quite a while. Until today.

Today, I dusted them off, and then tried to figure out where I left the rig. In the end, I just plugged in the new chips, hooked up a set of ear buds, and fired it up.

This time, and voila. The AVR is running! I hooked up paddles, and the keyer seems to work fine. I can hear the QSK thump in a little bit when the receiver kicks back in, but all seems well. I’ll drag out my oscilloscope and test voltages and the like: when I left it last time I thought the oscillator wasn’t actually oscillating, but now that things are hooked up, maybe all will be better. Now, all I need to do is find the two parts that I need to finish it: the BS170 that serves as the final amplifier and the BNC connector so I can hook my antenna to it.

And then, I’ll have to brush up on my CW. I found my Gordon West CW CDs too. 🙂

An AO-51 recording, and an attempt at a QSO…

Well, it’s been quite some time since I tried to work any of the FM birds, but I dusted off my TH-D7A, my voice recorder and my Arrow antenna, and decided to give it a go. It was pretty busy, and as usual I found it a bit difficult to get in. I got myself in the downlink once, and KB6LTY responded, but I couldn’t get through to confirm the QSO. Oh well. I’ll give SO-50 a try later, it is usually a bit more civilized there, and we have an 85 degree pass coming up shortly.

Until then, here’s a recording of the pass, a bit scratchy in the beginning, then it gets better.

2010-12-12-AO-51

Congratulations to SpaceX, and a new Cubesat!

Lost in yesterday’s thrilling launch of the SpaceX Falcon-9/Dragon launch was that during their flight, they also apparently deployed a cubesat: CAERUS (which is apparently Greek for “opportunity”). It has a 900mw FM AFSK beacon downlink on 437.600, and operates under the amateur callsign KJ6FIX. I have not as yet been able to locate TLEs for the satellite, so I’m not sure of its orbit, period and the like, but it might be good to try to give it a listen.

Information Sciences Institute – CAERUS.

Addendum: The Falcon9 also carried a nanosatellite for the Army.

The BPSK1000 Telemetry Modem for ARISSat-1

The legendary Phil Karn, KA9Q is apparently the brains behind the digital telemetry modem that will be used aboard the ARISSat-1, a satellite designed to be tossed off the ISS sometime next year. From his paper:

ARISSat-1 will carry a new telemetry modulation and coding scheme, BPSK1000, designed to handle the severe fading often encountered with low orbit satellites without attitude control. Its performance and the link budgets for the ARISSat-1 spacecraft are such that reliable reception should require only a simple whip or ground plane antenna, a conventional 2m SSB receiver, and a reasonably modern personal computer with audio A/D input.

BPSK1000 uses differential binary phase shift keying (DBPSK) at a channel symbol rate of 1 kHz in a SSB bandwidth. With constraint length 7, rate ½ forward error correction (FEC), the user data rate is about 500 bits/sec. HDLC framing provides application flexibility (including the ability to carry AX.25 in other applications) and a deep (16 second) convolutional interleaver provides strong protection against fading.

The BPSK1000 Telemetry Modem for ARISSat-1

I wasn’t able to find any links to the software, but I’m not panicking, since the launch is several months away, but worth looking into.

While googling, I found that KE9V had mentioned this a couple of days ago. One of his comments asked “Why not just use AFSK/FM like all the traditional packet satellites?” The reason is simple: it doesn’t work as well. The way these things are usually evaluated is in terms of Eb/N0, which is the “energy per bit, per unit of spectral noise density”, usually defined for a given error rate (10^-5 seems typical). For AFSK/FM at 1200 baud, Eb/N0 works out to 24db. For Karn’s proposed technique, it works out to a mere 6.7db. In practical terms, this means the satellite can operate at much lower power levels (it’s going to only be sending out 100mw) and the signal can still be reliably detected by omnidirectional antennas.

Very cool.

Software for the SDR-IQ

Earlier this year, I blogged about my acquisition of an SDR-IQ receiver, made by RFSpace. I hadn’t had it hooked up for quite some time, so I dusted it off, fired up the Spectravue software that drives it, and did some scanning around the bands. Yep, it still works. I really like Spectravue for the most part. It isn’t that hard to get used to, and allows you to easily scan the ham bands looking for signals.

But the one thing it does seem to lack is some noise reduction. Listening to hours of white noise is a bit fatiguing, and I was hoping that I could find something that would make listening a tiny bit better.

Enter SDR-Radio. It’s a spiffy program that knows about the SDR-IQ, and among other things seems to include three different types of noise reduction, as well as some better (IMO) automatic gain controls. There are aspects of the interface that I find less intuitive, but overall it is a very pretty and well done program. If you have a supported radio, check it out.

SDR-RADIO.com > Home.

GPS Visualizer

GPS visualizer takes all sorts of data from various GPS type hardware/applications, and can convert into bunches of other output formats, like Google Earth’s KML files, GPS files, output for Google Maps, and JPEG/PNG/SVG. It’s free. Stashed for future reference.

GPS Visualizer.

APRS experiment: OpenTracker + Kenwood TH-D7A

On Saturday, I decided that the missus and I needed to do two things: get out of the house and get some exercise, and test my OpenTracker. So, I thought that we’d drive out to Mount Diablo, get a hike around, and then see how well the combination of my TH-D7A and the OpenTracker worked. For added difficulty, I set the TH-D7A to use the “EL” power setting, which is a very minimal 50mw, fed to the mag mount whip on the top of my Expedition.

Here’s the path it recorded:

OpenTracker, Kenwood TH-D7a at 50mw

It worked pretty well, which bodes well for the balloon launch. It suggests that power levels of a couple hundred mw would be entirely adequate for balloon launches.