Monthly Archives: September 2007

What does RTTY look like?

I recorded some in Audacity. Here you can see the spectrum display. It wheedles back and forth between two tones which are clearly visible. You can also see some considerable fading in the signal. Them’s the breaks of propagation.  If you look really closely, you can see another, weaker signal in the spectrum directly below it which fades out entirely as the band conditions change.

RTTY viewed as a spectrum in Audacity

Signals from the Galapagos — HC8N

While tinkering with my little TenTec receiver, I’ve been hearing a ton of radio teletype signals. Apparently it’s the CQWW RTTY contest this weekend, which my ham friends who are more into all this say is the biggest contest of the year. I’m more interested in actual conversation, so I was kind of bored, but heard signals from all over the U.S., including Texas, Arizona, and Minnesota. But then I saw someone calling CQWW HC8N, I wasn’t sure where that was. (Each country has a different set of letters to start their callsign). I looked it up.

HC8N — Home

That’s from the Galapagos Islands! Awesome! Signal was really booming in here too.

Someday I’ll have to get a transmitter. 🙂

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Pascal Implementation

Pascal is one of my least favorite languages, but reading about how compilers work and examining real code of the (actually fairly simple) system works is fun. Check out:

Pascal Implementation

Included here is the Pascal source of a public-domain Pascal compiler and interpreter, the P4 compiler and interpreter. It is coded entirely in Pascal, and produces a high-level so-called intermediate code as output. The program ‘pint’ is an assembler and interpreter for this language.

The complete text of the book explaining the compiler is also available.

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TenTec 1056, in a case!

Well, I finally bored some holes in the case (kind of banging it up a little in the process, next time, I’ll put tape over all the edges) and mounted my radio in a real metal case. After warmup, it seems quite a bit more stable, and there is less problem with microphonics and frequency wandering now that it is inside.

TenTec 1056, in its casePardon for the slightly bad picture, I snapped it using PhotoBooth from my apple laptop, since I couldn’t find even a single SD card for my real digital camera. Sigh. I’ll get a better picture up later.

I got ready just to catch some 30wpm code practice from W1AW. That’s too fast for me, but fldigi did a pretty good job of decoding it. I also caught a bunch of RTTY stations calling CQ, but no real QSOs.

I’ll be having more fun with this. Now, to put all the tools away.

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Pattern for My TenTec 1056

Well, i was playing with the TenTec some more, and noticed that it wasn’t very mechanically stable . The VFO wanders considerably just from the capacitance of objects in its vicinity, by as much as a couple of hundred Hertz. It’s time to get this thing mounted permanently in the box I ordered for it. I’m not sure that will help, but it certainly won’t hurt either.

I sat down for a few minutes, and typed up some raw PostScript to design the front panel and the base pattern, along with markings for all the holes in the case. I’m betting the holes in the circuit board are #4 screws, which require a 7/64th inch hole, and the potentiometers in the front require 5/16″ pilot holes. I’m going to print these out on big label stock, and then cut them and mount them on the case as patterns for drilling.

Don’t know if this will be useful to anyone else, but here ya go.

PDF Template for TenTec 1056

I still have to figure out what other connectors to add. I suspect i’ll put a regular SO-259 to connect the antenna, sockets for an external speaker or headphones, and maybe a BNC connector for adding an external frequency counter. But this is a good start.

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Recording from my TenTec 1056

Well, I feel stupid. After days of figuring out why I was getting an ugly feedback squeal coming everytime I tried to plug in my TenTec 1056 into something. Finally, today, on a total lark, I swapped out the cable. And… voila. Worked perfectly. So, here’s some Morse code recorded directly from my radio (recorded using GarageBand):

Recording from my TenTec 1056

Addendum: You could read the morse directly from this spectrogram that I made of the resulting audio this improved spectrogram that I made of the resulting audio. You can see the obvious strong signal at the bottom, but at least three or four other signals scattered up in frequency from there.

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Addendum: the two loudest signals in the above translate to:
= SEE U R IN MN EARL BUT NOT SURE WHERE BIGFORK IS LOCATED = I LIVED IN MN
MANY YEARS AGO

and
BUT I GUESS WHEN WE GET MORE IN TO WINTER THINGS GO BTR AT LEAST NOT SO MUCH QRM = HR ON 40 ES 80 SU

Ten Tec assembled, and it appears to work!

Ten Tec 1056
Well, I decided to tack together my Ten Tec 1056 receiver kit. It took me about three hours to assemble. It was pretty straightforward to assemble, only one thing confused me: a group of three resistors which were supposed to be 220K ohms didn’t seem to be in the package, however, a quick inventory found three otherwise unused ones which were all 160K. So, I used ’em. I was also a bit concerned that when I tested the audio stage half way through assembly, I could hear the 60hz buzz when touching one of the resistor leads, but tweaking the bandpass control didn’t seem to help modify the noise background. I harumphed, but decided to just press on.

It took me a while (and a brighter light) to find the final two capacitors (they include a bunch, so you can build it for any band). But finally, my squinty eyes revealed the right components and all seemed to work. I hooked it to my old 13.8 volt regulated supply, added 20 feet of random wire as an antenna, and cautiously powered it on.

I heard the rush of noise. It’s got plenty of audio gain. Turning that down, I tweaked the main tuning inductor, and… voila! Morse code signals!

I’ll tweak it around some more, get it in a case, and wire up some connectors so I can hook it to my dipole. But so far, mission accomplished!

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YASI — Amateur Radio Interferometry

Wow. This is just too cool. I got my TenTec 1056 receiver kit in the mail the other day, and was just randomly searching for links on the internet giving people’s experiences with it, when I ran across this:

YASI

This website describes the construction of an amateur radio interferometer using equipment that isn’t much beyond the budgets of other typical hobby activities. In particular, the “poor man’s version” uses two of the TenTec receivers that I bought, each wired to a common local oscillator. This enables them to correlate the signals from two widely separated antennas, and thereby determine the direction of radio sources in the sky.

It’s a fascinating project. Very cool. I’ll be back to read more later.

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Part of the 40m band, viewed graphically

This isn’t really all that amazing, but I thought I’d place it here anyway. As part of my experiments in decoding PSK31, I recorded a minute of the 40m band and saved it out as an uncompressed 8000 samples/second WAV file. This morning, I dusted off the fftw library, and wrote a 30 line stub program to convert the one minute of audio into a graphical interpretation of the spectrum. If you click the link, you can see what that looks like:

Audio Spectrogram of the 40m band

Frequency increases from 0 to 2khz from left to right, time increases downward. Each scanline represents about 1/50th of a second. Horizontal, fuzzy lines are usually temporary bursts of static. The strong vertical lines are each individual transmitters, all operating the PSK31 mode (except for one brief unmodulated tone of undetermined origin, see if you can spot it). When the trace separates into two distinct lines, the transmitter is in a pause state: the person at the keyboard is typing slowly. One person obviously types quite a bit slower than PSK31 can transmit.

There is also some fairly clear indication of fading, and when the unmodulated carrier comes on, you can see that it is so strong that it might be desensitizing the receiver.

Anyway, I just thought it was fun. The demodulator requires some filter design and digital PLL design that I don’t completely understand, but this was a first step. Incidently, the amount of time to do the FFTs here is so close to trivial as to be not worth mentioning.

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Power Spectrum of the Audio Signal

Addendum: Above you can see the total power over the entire minute, scaled logarithmically.  In it, it isn’t hard to see that around 0.4 (corresponding to 3.2khz), the background noise ramps off considerably.  This is just the crystal filter in the Drake ramping off background noise.  You can also see its response below about 300hz is quite low, and can easily recognize peaks which correspond to the carriers and PSK31 signals in the spectrum that I linked above.  Neat.

Rob Pike on Newsqueak

Rob Pike is an interesting guy. Formerly Bell Labs researcher, now at Google, Rob Pike has not only done more innovative and development in operating systems and programming languages than I can shake a stick at, he’s also built telescopes, appeared on Late Night with David Letterman, and was the 1980 Olympic Silver Medalist in archery for Team Canada. What I find compelling about his work is his ability to think outside the current paradigms offered current operating systems (mostly Unix or worse) and current languages (mostly C++ and Java or worse) and see what we could really do.

In the video below, he dusts off some work on the interesting language Newsqueak, which had many good and innovative ideas which were not widely adopted in successive language designs. This is part of Google’s lecture series on programming languages. Enjoy.

Advanced Topics in Programming Languages: Concurrency/message passing Newsqueak

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Addendum: Here’s Rob’s page at Google, which has links to many of his papers.