While looking at the hadie high altitude balloon project, I got to thinking about making a microcontroller that could send RTTY. I knew that traditional Baudot (more properly the ITA2 code) was a five bit code with codes designed to switch back and forth between “letters” and “figures”, but I had never looked at the actual matrix. Here is the diagram from Wikipedia:
Tell me, is there ANY rhyme or reason to this layout? It literally looks like they just scattered the letters and numbers onto the codes more or less completely at random.
I was just curious: can anyone tell me what I am missing?
While listening to the Amateur Radio Newsline podcast this week, I was interested to hear that a group of hams from Ireland had launched a balloon which transmitted digital pictures back from the balloon while it was at altitude, using a version of dl-fldigi. While I was familiar with fldigi, I hadn’t heard of this version, so I did a bit of searching on the web.
First of all, you can find details about the hadie high altitude balloon project here:
Sadly, the balloon had a slower than predicted rise rate (2m/s instead of 3.5) and so overshot England after floating across the Irish Sea and landed in the North Sea. But it’s very cool that we got these live photos back.
Digging a bit more revealed this nice project web page which had many details about the hardware and software they used. They used a serial based camera module previously sold by Sparkfun (now apparently retired), an NTX2 module from Radiometrix which broadcasts on 434.075Mhz, and a cpu based upon the ATmega644P chip. The flight software appears to be written in C, and reads the data from a GPS and the camera module, and repackages it in a custom format called ssdv for transmission over 300/600/1200 baud 8 bit RTTY which can then be decoded by a custom version of fldigi known as dl-digi. Very neat. The radio module that they use has an output power of just 10mw, and yet was successfully decoded over distances greater than 500km. What’s kind of cool about this technique as opposed to (say) the analog Robot32 mode that ARISSAT-1 uses is that the image is broken up into packets, which are transmitted and received independently. The dl-fldigi can send any received packets to a central repository, and thus if any station successfully decodes a packet, then the image can be reconstructed (something that is difficult with analog SSTV).
I didn’t have much to add to this, I just wanted to stash this for later. While the images they got don’t really compare to some of the awesome HD footage that we are seeing shot with GoPro cameras, the immediacy of this seems very appealing, and it’s a good technical challenge.
For some reason, I’m getting back into the universe of QRSS, or very slow Morse code. I goofed around with this for a while, writing some software to record audio and produce the necessary FFTs so that you can read Morse from these incredibly long Morse messages, but lately haven’t done much lately.
Hopefully, that will change during my time off for the holidays.
Somewhere in a junkbox, I built this circuit (from Hans Summers, G0UPL):
It’s really just a Colpitt’s oscillator, with a reverse biased LED acting as additional capacitance to “tune” the frequency around the nominal crystal frequency. When I built this circuit, I played around a bit with using an Arduino with an digital to analog converter to drive the LED back capacitance, and that worked fairly well. Here’s a timewarp back to that project, in the form of two of my earlier YouTube vids:
It worked, but I never put it on the air. But I got to rethinking it a bit more, and thought that maybe I’d assemble a new version and see how much I learned. I’ve got some ideas for improvements:
Make it “real”. Think about the layout a bit, and built it to be completed inside an (Altoids?) case.
The 4.7pf cap is too much to be driven by 0-5v (it induces too much frequency swing). Use a “gimmick” cap in its place.
Build in a small “dummy load” (just a 50ohm resistor), and add some test points so you can monitor the supply voltage and current from (say) an Arduino. It would be interesting to monitor temperature as well.
Oh, and use an Arduino to key it. Or maybe just an ATtiny.
Spend some time thinking about solar powering it.
I also was considering making a better dedicated antenna for it. I suppose I could just use a 30m dipole, but I think it might be fun to try something a bit smaller. Alan did some experimentation with a center loaded short dipole which might be fun, but I’m still pondering that.
The micro-power transmitter is fun, and unlikely to cause anybody any anguish, but might also be a bit hard to get any real DX with. So, I started thinking about what I needed to change. Higher voltage, to generate more power. A buffer and power amplifier to generate maybe 100-200mw. And a harmonic filter, so I could be a good citizen. But then I realized something: Hans was offering a kit that had all of those features already, and for about $15 US. So, I’ve got one of those on order too.
I hope to be on the air come the New Year. Stay tuned.
I mentioned that Roger, G3XBM was shifting from the very low frequencies to much higher frequencies. His interest has already uncovered some links that I hadn’t seen before. One very cool thing was his discovery of a local 477Thz beacon (that’s red light) that is aimed roughly in his direction at a distance of around 30km. The beacon is the work of GB3CAM, and uses ten 10mm red LEDs, running with about 400mw DC power input. What a cool idea! The entire circuit consists of a PIC processor and an XR2206 monolithic function generator.
I’ve mentioned Codec 2 a few times in the past, but for those who don’t rememember, David Rowe has been working on a very low bitrate codec optimized for speech applications. This is of interest in amateur radio because we don’t have a suitable speech codec which isn’t patent encumbered (if for instance, DSTAR’s AMBE codec was not encumbered by patents, we could create open source versions which would be compatible with the DSTAR network).
David just announced that’s he’s got the codec down to 1400 bits per second. Check it out: it sounds pretty good.
I’ve stopped hacking on my Arduino/Gameduino satellite tracker for now. Here’s the final video demonstrating it running:
I’m currently working on the final schematic which will be posted on this permanent page. The code will be available github.com, for right now, it includes the library that I wrote that does the satellite prediction. I’ll be updating the code sometime later this week.
If you take it and use it, let me know: it will motivate me to do more with the code.
I was looking for beacon circuits, and ran across VK3YE’s USB powered 40m transmitter. Unlike most simple beacon transmitters, this one transmits double sideband, which makes voice transmission possible. I like the basic idea!
Very cool. He’s also got an awesome awesome YouTube channel, with over 180 vids uploaded. Lots of good information on crystal radios, homebrew, and low power operation. Snoop around! I was particularly intrigued by this video showing low power SSTV operation:
Legendary QRP hacker Steve “Melt Solder” Weber has some awesome stuff on his website, particularly if you are interested in homebrew ham radio gear. (Indeed, it appears he’s about ready to offer his legendary ATS-4 5 band rig kits again, experienced kit builders might want to check it out.) But what drove me to his website this morning is quite clear exposition of buck and boost voltage converters in PDF form. Remember my ATtiny13 powered Halloween pumpkin? It was inefficient: about half of the power consumed in the circuit was simply lost as heat in the current limiting resistor. Had I read Steve’s exposition a month out from Halloween, I might have tried to do better.
Here’s the relevent circuit cribbed from his PDF:
Pretty simple! A couple of things to note: the NDT2955 is a logic level P type MOSFET, which turns fully on with a gate threshold of just 4V. Readers may remember that my own experiments with the IRF510 didn’t succeed in some small part because the IRF requires 10V to switch entirely on. Secondly, the ATtiny13 is powered directly from a 6V supply, through two diodes. These are there simply to drop the voltage to the 5.5V level which is the maximum safe amount. The ATtiny13V is very forgiving on voltages, and can operate all the way down to 1.8V, long after the batteries will have given up the vast majority of their power.
I’ll try to work through the equations and design a similar driver for my 1W Cree LEDs. To build it, i’ll need to come up with an appropriate MOSFET. Stay tuned.
Like nearly everyone in the Bay Area, I spend too much time in my car, and one of the ways that I endure it is by listening to a lot of podcasts. Most of these are technical in nature, and in particular, I’ve sampled most of the ham radio podcasts out there. One of the primary sources of news is the Amateur Radio Newsline, and most weeks, I download it and listen to it.
And increasingly, every time I do, I shake my head and wonder why I am bothering.
Here’s the thing: it’s hardly got any amateur radio content on it at all.
Seriously. Go download any audio transcript, and try to find an actual story that contains something that actually enhances your enjoyment of amateur radio.
Let’s see how long it takes this week’s episode to get to a story that’s actually about ham radio:
News about the earthquake in Turkey. Yep, they had an earthquake. TRAC, the Turkish amateur radio society is helping out, Other than just saying that amateurs should stay off specific emergency frequencies if they are in use, no hint about anything any radio amateur can do. No names. No place to send donations. No mobilizations.
The FCC approved a set of new BPL rules, which don’t protect amateur frequencies from harmful interference. Might be interesting to people out there, but again, nobody to contact, no call to action, no names.
The FCC is going to have a national EAS test. Nothing to do with amateur radio.
Lots of intruders on 10m. Yes, illegal operators abound, particularly on 10m, and now that it is heating up, we’re hearing them. Is this news?
The National Capital Radio & Television Museum needs some space. Sounds like a fun place. Rather than talk about it, the story was mostly about their increasing lack of space and lack of handicapped access.
Odessa, Texas is considering a no-texting law. Yeah, hams get all upset when any law that might remotely keep them from operating mobile seems possible, but it’s not clear that this law applies to hams. My guess is: it doesn’t.
Enforcement actions. This is what annoys me absolutely the most about Amateur Radio Newsline. In every single episode, and sometimes even more than once, they take time to run essentially the same story over and over again (this week, there were enforcement actions against people in San Francisco and Florida):
Somebody was operating an unlicensed radio transmitter, most often which interferes with traditional broadcasters or police, fire, or other public safety services.
Said person is tracked down, and is found by the FCC to have been naughty.
The FCC fines them some amount (ten thousand dollars is typical), and gives them the customary 30 days to appeal.
This blogger dies a little inside.
Here’s the thing: I don’t care. I can’t imagine that anyone cares. Operating an illegal transmitter is, well, illegal, but it has nothing to do with amateur radio. If I never hear the terms “notice of apparent liability” or “customary 30 days to either pay the fine, or file an appeal”, it will be too soon.
Gasp! Something actually ham radio related! A new 10m Digital Net! Huzzah!
We made it almost to the second break before we got something which might actually enhance your enjoyment of amateur radio.
Okay, I ranted enough: if you’ve made it this far, you deserve to have something nice tossed your way. Instead of listening to Amateur Radio Newsline, check out Martin and Colin’s ICQ Podcast. A father/son team, this good natured duo of hams from the UK pack together news, a feature, and typically propagation report or some other guest into each bi-weekly episode. Ham radio news, gathered and distributed by hams. I like it.
I’m not much of a contester (not any kind, in fact) but this weekend is one of the biggest: the CQWW SSB Contest. Expect the bands to be completely awash with chatter from 0:00 UTC October 29th through 23:59UTC October 30th. I doubt I’ll do much, other than maybe hookup my SDR-IQ to scan around some of the higher bands like 17, 15 and 10m to see what’s up.
This morning, I consulted the little revolving map over there in the left column, and found that I had passed 99,000 views. I reset that counter back in February, and since then nearly 100K people (or more realistically, 99K robots and maybe 1K people) have viewed a page here on brainwagon. I’d like to thank all of the people who take time to read my chaotic jumble, and would especially like to thank those who take the time to comment. While this blog is mostly a sort of personal journal, your participation makes the time I spend here seem more valuable.
I hope in the next year to continue to improve and expand the kind of materials that I post here, documenting more of my own projects, and linking with more people who share a common philosophy. I hope you will stay tuned and participate going forward.
A few months ago I acquired a used IC-735 from my boss, and other than getting it hooked up and using it for the occasional bit of RX, I haven’t actually powered it up and done any QSOs with it. Part of the reason is my inherent “mic-fright”, but I also know that my impossibly low and decrepit 40m dipole is simply the wrong thing to use. I’ve been thinking of making a better antenna for the higher bands (20m, 17m, 15m, and 10m) but I haven’t gotten around to it.
But today, I was spinning around on 15m, and heard the T32C station calling. I’ve been reading a lot about how easy they were to work, so I thought I’d give it a try. I summoned up some courage and responded to the call for CQ. “Kilo Six Hotel X-Ray”. No dice. I gave it a couple of more tries. It was obvious he wasn’t hearing me.
After 10 minutes, I spun the dial down to 17m and hunted to see if I could find him there. I heard him calling on 18.145, operating split and listening 5khz up. A few minutes of fumbling made me figure out how to operate split on the IC-735, and I called him.
Bam. Immediate success. We exchanged 5-9 signal reports, and he goes in the log book.
This was also my first contact logged on 17m.
When the QSO was done, I tried to remember exactly where Christmas Island was. I was initially confused, because it turns out there are two islands known as Christmas Island. The first (and the one where T32C is operating from) is Kiritimati, in the mid-Pacific. The other Christmas Island is an Australian territory, and lies north west of Australia in the Indian Ocean.
Wow. Pretty good jolt today. I was sitting in my office when I began to feel some high frequency shaking, starting weak, but then growing sharply in intensity. I’ve been in California long enough that such things don’t usually perturb me too much, but this one was as strong as I can remember in the twenty years I’ve been living here (I missed the Loma Prieta earthquake in 1989). The noise was loud. Less rolling than I’ve felt before, but lots of energy in fast shaking. I bolted out of my office, but didn’t even make it twenty feet before it stopped. So, what did I do? Headed back to my desk to check the Internet.
Turns out it was a 3.9 (downgraded from an early estimate of 4.2) but less than three miles or so from where I am. Here’s the seismogram from Pinole Ridge:
A pretty good ride. I think I’ll head home a bit early to make sure the cat is okay.
While I’m still trying to shake a respiratory infection, I’m hoping that by the weekend I’ll be hale and hearty enough to attend this years Pacificon 2011. It’s a bit of a drive for me in the North Bay, so I suspect I might be there only for Saturday, but it’s remotely possible I’ll try Sunday as well. If any readers are going to attend and want to contact me and maybe say “hi” or go have lunch, feel free to contact me beforehand via email, or via twitter (@brainwagon) during the conference. I’ll also be wearing my spiffy K6HX nametag, and probably a hat with all sorts of nutty pins stuck in it.
My cat Scrappy decided it was time to film a brief progress video of my Arduino/Gameduino satellite tracker. I completed the basic port and testing of my Plan13 implementation to C++ for the Arduino, and got it running pretty well. It doesn’t seem to be much more compact than Bruce Robertson’s qrpTracker code, but it isn’t any worse, and I like the way I modularized and call it a bit better. Eventually all this code will be released on this website for anyone crazy enough to want to build one for themselves.
