It’s that most auspicious of holidays: National Talk Like a PIrate Day. All ye scurvy dogs, y’ed best be ex-agg-eratin’ yer ayes and arrs lest Davy Jones rise from the briny bottom and haul ye back to his locker.
And now, a scene from the best pirate movie of all time:
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!
[tags]Amateur Radio,Electronics,Kit,My Projects[/tags]
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:
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.
[tags]Radio Astronomy,Amateur Astronomy,Radio[/tags]
The best description that I’ve found of PSK31 decoding is actually in the WinPSK Technical Manual. Its remarkably informative.
WinPSK Technical Manual
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.
[tags]Amateur Radio, Digital Signal Processing, My Projects[/tags]
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.
Heh, I was following an innocuous link this morning, and found this little rant by Linus (yes, that linus) about the use of C instead of C++ in git. He could have been channelling me.
[RFC] Convert builin-mailinfo.c to use The Better String Library.
[tags]Rants and Raves, C++[/tags]
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
[tags]Rob Pike,Newsqueak,Google Research[/tags]
Addendum: Here’s Rob’s page at Google, which has links to many of his papers.
So called “steam punk” has been getting fairly popular lately. The idea is to take modern implements and reimplement and restyle them as if they were constructed in the Victorian era. It’s kind of silly in a way, but there are lots of opportunities for interesting craft projects and techniques. Today, I encountered this interesting page on copper plating and salt etching, which were really quite interesting. I might have to try this.
Copper Plating and Etching Altoids Tins
[tags]Steam Punk, Arts and Crafts[/tags]
Yep, I’m still on my radio kick. Ran across a link to this interesting book, available for download as a bunch of PDF files that entices you to homebrew your own ham radio equipment. Cool.
Book Copyright (c) 2006, Frank W. Harris / HTML and PDF assembly Copyright (c) 2006 AmSoft
In one of my previous posts, reader Jim suggested that:
The use of digital modes in amateur radio really puzzles me. The beauty of radio is its technological simplicity. If I want to communicate digitally, there are wonderfully complicated and beautiful ways to do it on the Internet. But give me a few transistors and some wire, and I can communicate around the world, at least in principle.
I can understand his point, but I don’t agree.
First of all, it is simply a fact that while in principle one can build a transciever out of a couple of transistors, a crystal and some wire, that’s simply not what the vast majority of hams are doing. To draw an analogy, if building your own transciever and running two watts into a chunk of wire is analogous to backpacking, the vast majority of hams are either picnicking (using 2m ht and mobile rigs via repeaters) or are driving enormous RVs around. To be fair, backpacking, picknicking and driving an RV are all pretty fun things to do, and it would be a mistake to pretend that they aren’t, but they are also somewhat different.
I have a general philosophy that tells me that the only way to really understand something is to do it. Build stuff. Figure out why it does or doesn’t work. Do it again. Hence, the QRP/homebrew world of ham radio has considerable appeal. But to me, QRP has an almost unnatural obsession with CW operation. There is dogma in the world of radio amateur world that says that “CW gets through when nothing else will”. It was a reasonable thing to say back when your alternatives were AM and SSB. But it’s wrong. Other alternatives do exist, and they really aren’t very complicated at all. A $4 dsPic can <em>replace</em> lots of complexity in traditional transceiver design, and enable communications in situations where CW would just fall to the ground. Yes, it converts an analog hardware problem to a digital software problem. I don’t view that as a bad thing.
[tags]Amateur Radio[/tags]
Well, after listening to one of the soldersmoke podcasts which described the old Drake 2-B as one of the premier communications receivers of all time, I began eyeing mine in a slightly different light. I’ve had this little guy in storage for eight years or so, and my experience with it was that it was pretty deaf. But I began thinking: to be fair, I’ve never used it with anything but a chunk of random wire. Might my experience be different with a more proper antenna?
Clearly a test was in order. I stopped by HRO today and picked up a simple 40m dipole. (Yes, I’m lazy, I could have built it myself). I have 50 feet of RG58 feedline from Radio Shack but couldn’t locate it, so once again, I couldn’t hook up the antenna properly. Still, I hoped it would make some difference. I unwound only one leg of the dipole, which stretched all the way across my living room. I left the other coiled behind the receiver. Hardly optimal. I hooked up a little stub of feedline that I had.
The CW band (Morse code to most of you) was alive with signals, where previously I might have had difficulty finding one. Huzzah! Clearly it was much better. I don’t know why I was surprised, but I was. But I wasn’t ready to stop then. I remember that I had a “digipup” live CD floating around. This is a distribution of Puppy Linux especially for ham radio, including the program fldigi, which can decode many of the digital modes that are active on HF. I booted my old (slightly unreliable) laptop into it, and set about looking for PSK31 signals.
PSK31 is a relatively new (< 10 year old) digital mode based upon BPSK (binary phased shift keying). It emits a sort of warbling sound, the peaks of which are separated by a mere 31 hz. It has rapidly become very popular with hams because of its ease of use, its speed, and its very narrow bandwidth.
PSK31 activity on 40m is supposed to be centered around 7.035 megahertz. I suspect that my calibration is off, because I found signals mostly near 7.050 khz on my band, but several were active. I clicked on one… and voila! Digital decoding! Click on the thumbnail at the right for a closer look. This wasn’t even the strongest signal, and I was receiving 100% copy.
I was psyched. I am psyched. I have a little PSK80 kit (a dedicated transciever for PSK31 on 80m) that I hope to get on the air soon, but this taste was fun!
Addendum: A closeup of fldigi can be seen in this picture.
[tags]Amateur Radio, PSK31[/tags]
The original Apple iPhone was released on June 29th of this year. 68 days later, Apple announces that they are cutting the price by $200.
I guess we can infer from this that Apple decided the iPhones weren’t selling as well as they would like, and that the new (very good) price point will help stimulate sales. But it’s a bitter pill to swallow for those who bought at the $600 price, with some expectation that it would be the going rate for more than sixty days.
I hope you enjoy my $200 Apple.
I continue to love my iPhone incidently. I’d just love my $200 too.
[tags]Apple,iPhone,Infuriated[/tags]
Well, not the rear panel of my Drake 2B. The markings on the back of mine have faded considerably, so much so that it is hard to read the lettering associated with each of the connectors. Luckily, I found a good picture of the rear panel on the web, which I’m archiving here for the moment.
[tags]Amateur Radio, Drake 2B[/tags]
Recently, my brain has shifted back into ham radio mode. My license had expired back in May, and I decided to renew it, and as a result, my interest was also somewhat renewed. I’ll probably bore you some more with this in the future, but I was down at Ham Radio Outlet, picking up a book, and the sales guy recommended a podcast dedicated to homebrew radio:
There have been 65 episodes thusfar, and I’ve got ’em all on my iphone. You have to be pretty hardcore to find it interesting, but if you are a radio amateur, you might find it interesting. Check it out.
[tags]Amateur Radio[/tags]
