The other day I was watching the 1939 movie The Adventures of Sherlock Holmes, a rather fun film staring Basil Rathbone and Nigel Bruce. Early in the film, the maniacal Professor Moriarty (played with great zest by George Zucco) is menacing his butler Dawes for allowing one of his prize orchids to wither while he was in jail awaiting trial for murder. He laments the injustice of him serving six weeks in jail for murdering a man, while a more suitable punishment for murdering one of his flowers would be to be “flogged, broken on the wheel, drawn and quartered and boiled in oil”.
Immediately after, he takes on of his orchids and presses it meaningfully into a copy of Baedeker’s London and Its Environs. I love old books, so I looked i up on archive.org. And, of course, they have digitized it, at least the 1901 version. It’s a traveler’s guide, carefully documenting all the kinds of things you might want to know about when visiting London at the turn of the last century. Neat! What’s also cool is that Moriarty puts the orchid at a place where there is a map or diagram on the left side of the book. A few minutes of perusing reveals that it’s a map of the Tower of London, which plays a key role in the story. Nice bit of foreshadowing! Digging around, it kind of makes me wish that I had a copy, and as luck would have it you can get a digital version of the 1899 edition for your kindle. It also appears you can get facimiles of original Bradshaw railway guides for about the same. If I ever return to working on my Sherlock Holmes story, I’ll have some useful references.
Scott Haley mentioned my old Hellduino post on Facebook: a simple project that used an oscillator powered by an Arduino to send Hellschreiber, a kind of simple fax mode invented by Rudolf Hell in the 1920s. I did this mainly as a simple test, inspired by Steve Weber, KD1JV’s “temp2morse” project. But unfortunately, that page seems to be gone, so the schematic isn’t available. It’s not a huge deal: almost any Colpitt’s oscillator would do in its place, with the main power rail being powered by a digital output on the Arduino, but I thought I’d see if I could find one suitable. I’ve built this low power oscillator documented by Hans Summers before, it’s probably overkill (it’s meant to drive a 50ohm antenna, and actually radiate some single digits worth of milliwatts). K7MTG’s HF Thermometer project was the inspiration for Steve’s, so is probably a good place to start. If you look at his schematic, you’ll see it has no antenna, and no power amplifier. It is actually a bit more sophisticated than my first test circuit was: L1 and C3 form a tuned circuit, which probably makes the waveform a bit more sine-like (if you look at my video, you’ll see the waveform isn’t ideal). To convert this circuit to send Hellschreiber is just a question of software, since Hellschreiber is (like Morse) just sending dots at the right time.
Addendum: Jeff Kellem was nice enough to do some heavy lifting and find a copy of the original schematic for Weber’s temp2morse project:
He found it on LB3HC’s blog. The original article (without images) is archived via the Internet Wayback Machine: click here to enter time vortex.
I’ve been doing a bunch of reading about digital ATV operations lately. I was originally motivated by hearing about the HamTV project aboard the ISS. Back in 2007, I got re-energized into ham radio by learning that for the 50th anniversary of Sputnik, the amateur satellite AO-51 would broadcast a cool message that I heard with a simple HT. I’m wondering if I’m having that kind of a moment now: the idea of creating a station to broadcast digital television seems challenging but doable.
While reading up on the necessary bits for a HamTV downlink station, I found that this little satellite receiver which sells for less than twenty-five dollars could be used to decode signals from the ISS. It receives DVB-S signals, which are used by direct satellite broadcasters like Dish Network. But in thinking about how to go forward with the project, it seemed to me like trying to aim directly for a satellite downlink station was likely to be a frustrating endeavor. It requires a number of different subsystem to work together, but trying to receive the DVB-S from the ISS (given an intermittent schedule) would be difficult to test together. So, I started looking for resources that I could use to build a similar terrestrial station, including both a transmitter and receiver.
A couple of cool links:
The DATV-Express board is a $300 exciter board that is in limited production. It seems very cool. Reading the Tech Talks on this site yielded a lot of good information, I’m particularly pondering the information in this one, about designing a digital TV station.
Another similar project, but available more as a board/kit is the Digilite project. An interesting variation of this project is the DigiliteZL project, which makes for a compact and interesting setup.
I also like the CQ-DATV magazine. It’s got lots of cool information, published in a series of magazines available in a variety of e-book formats. They also have a broad collection of interesting articles on the Digilite project, which I’m currently reading over.
I’ll probably stick to more experimentation with SSTV, but this stuff fascinates me, and I may have the opportunity to do something interesting with it in the future.