Tuesday, May 27, 2008
I am debugging again. Why can’t things just work?
I am debugging again. Why can’t things just work?
[This was drafted for the Palomar Amateur Radio Club newsletter, the Scope.]
Here are a few interesting tidbits from the AMSAT Space Symposium held near San Franciso in October. The big news seems to be that “software-defined transponders” (SDX) are coming soon. A traditional satellite transponder connects the analog IF output of a receiver to the analog IF input of a transmitter, repeating every signal on the uplink band, amplified, on a downlink band. An SDX modifies this by sampling the received signal, passing it through a DSP for processing, and sending the output samples directly into a digital transmitter. The digital transmitter is more efficient, and has a much higher dynamic range (80+ dB) than HELAPS (26 dB), the high-efficiency analog technique we’ve been using on transponders. The SDX demonstration at Dayton was a hit; everybody said it “sounds sweet” and it was quite robust to interference. As a nice side effect, the DSP can also make every input signal the same strength, so that “alligator” stations using too much uplink power won’t cause a problem anymore. Beyond that, the DSP can insert signals of its own (such as telemetry beacons) and even receive and act on uplink signals, all with no additional hardware. This technique is scheduled to be used not only in AMSAT’s big Eagle project, but also in AMSAT-DL’s Phase 3E satellite and much smaller satellite projects such as AMSAT-UK’s ESA SSETI ESEO.
Many small satellite projects are in the works. The US Naval Academy is working on ANDE, RAFT, and MARScom missions. South Africa AMSAT is working on Sumbandila (roughly, “Pathfinder”). AMSAT-ZL (New Zealand) is working on KiwiSAT. And that’s not to mention all the tiny “CubeSAT” spacecraft from educational institutions world-wide. AMSAT’s policy of concentrating on larger, high-orbit spacecraft and leaving the small, low-orbit spacecraft to the rest of the community seems to be working out well.
AMSAT’s Eagle project has been subjected to some hard-eyed engineering scrutiny. There’s a new mechanical design and a definite, feasible set of payloads now. An analog transponder will cater to the traditionalists with primary uplink on 70cm (U band) and downlink on 2m (V band), plus secondary uplink on 23cm (L band) and downlink on 2.4 GHz (S1 band). The U/V transponder should be usable over 75% of the orbit, but the L/S1 transponder will have a shorter access window due to antenna constraints. All these transponders will be implemented digitally with SDX, but ground stations will still use normal SSB/CW equipment.
Piggybacked on Eagle’s U/V transponder will be a digital short message service intended to be workable from a hand-holdable device. Envision a standard PDA clipped into a transceiver cradle, with a smallish omnidirectional antenna on top. AMSAT will have to develop the cradle and make it available to all at a reasonable price. Exact details of what kind of services will be offered are still to be determined, but expect something like internet Instant Messaging with some exciting twists. A hand-held satellite station could be just the thing in some emergency communications scenarios.
The primary service on Eagle will be a digital voice and data system called the Advanced Communication Payload or ACP, with uplinks on 3.4 GHz (S2 band) and downlinks on 5.8 GHz (C band). Steerable phased array antennas on the satellite will make these links available for 75% of the orbit. Two classes of user stations are envisioned. A user with a single 60-cm (about 2 feet) diameter dish will be able to operate digital voice or about 4800 bits/second of any kind of streaming data. A user with a big dish (6 feet) will be able to do the same, and also handle higher-rate data streams, fast enough for compressed digital video. Here too, AMSAT will make available ground station equipment kits to make it possible for anyone to get on the air without being a microwave guru or independently wealthy. The small dish service is specifically designed to be usable by apartment dwellers and those constrained by antenna restrictions: the small dish isn’t so different from a satellite TV dish. It will have to be pointed at the satellite, but only in one axis if the preferred orbit is attained.
The ACP is designed to take advantage of advanced digital techniques to maximize performance. It can handle about 20 simultaneous digital voice (or low rate data) channels, and all of the voice channels are transmitted as a single unified data stream. That means that a user station can, if desired, listen to any or all of these channels simultaneously. Each user’s uplink can be addressed to a logical channel, which might be a one-on-one QSO or a conference room. It’s all done in software. This opens some very interesting possibilities. As part of the campaign to get the ground station hardware into the field, I am hoping that AMSAT will make this system available for terrestrial applications, well before Eagle’s launch.
For those interested in antenna design, Tony AA2TX came up with two novel variants on the Lindenblad antenna. A traditional Lindenblad is four folded-dipole driven elements in phase, arranged in a square, each tilted 30 degrees from horizontal. It generates a nice omni sky-coverage pattern, circularly polarized, just the thing for low-orbit satellites with relatively strong signals. Tony’s design for 2m replaces the folded dipoles with regular dipoles, and uses a tuned coax phasing harness and slightly overlength elements to achieve low SWR without the mechanical complexity of folded dipoles and their twinlead feedlines. Tony’s design for 70cm eliminates the feedlines altogether, driving a Lindenblad-like array of parasitic elements with a vertical dipole at the center. Both designs are easy and inexpensive to build using hardware-store plumbing parts and aluminum tubing.
More information on Eagle and other upcoming satellites is available on www.amsat.org. The printed Proceedings of the Space Symposium will be available from the AMSAT store — www.amsat.org and click on “Store”.
I was asked to write up a page or two on the “genesis and early development” of the AMSAT.org web site. Here is what I submitted. The new webmaster is going to fill in the later history, add some comments on coming attractions, and wrap it up into a paper for the upcoming AMSAT Space Symposium.
Once upon a time, in the late 1980′s and into 1992, AMSAT was paying real money for key volunteers to use a commercial dial-up electronic messaging system called GTE TELEMAIL, and this budget item was becoming a problem. A cheaper alternative was needed so that more volunteers could be included. The obvious choice at the time was CompuServe, but that still cost money for each volunteer added to the system. A dial-up BBS could be run at a modest cost, but long distance was still too expensive for the users and multi-user operation would be a big deal. The discussion went on while Internet email snuck up on us.
Tom Clark (now K3IO, then W3IWI) began operating a spare IBM PC AT under his desk at Goddard Space Flight Center as tomcat.gsfc.nasa.gov. “Tomcat” (Tom C’s AT) supported the use of Internet email for AMSAT functions by providing callsign mail aliases (firstname.lastname@example.org) and bulletin mailing lists for the AMSAT News Service (ANS) bulletins and Keplerian elements (KEPS). It was also an FTP server for projects such as the original Microsat development and the TAPR/AMSAT DSP Project. Tomcat was operated semi-manually and began to take up too much of Tom’s time, while at the same time it became more and more important to AMSAT communications.
At the 1991 AMSAT Space Symposium in Los Angeles, an informal session about Tomcat drew a crowded room full of interested people. At that time there were over 200 users, and system overload was starting to set in. The Board could see that it had become an essential resource for AMSAT.
In May of 1992, AMSAT acquired a surplus Sun 3 workstation. Through the efforts of Brian Kantor, WB6CYT, it was installed in the network machine room at the University of California San Diego (UCSD), and registered as amsat.org. Tom put out a call for a new volunteer to take over day-to-day operation of the system, and Paul Williamson, KB5MU, was selected for the job. The new system started out with nearly 300 users and three mailing lists: ANS, KEPS, and a discussion “bulletin board” called AMSAT-BB. It also took over FTP duties. Other services such as private project mailing lists and additional public mailing lists (e.g., SAREX) were already in the plans.
Not everybody had Internet email in those days. Generally Internet access was at work or at school, and individuals at home had no affordable way to get on. That changed when CompuServe began supporting email to and from the Internet for users of its system. AMSAT was able to replace the big TELEMAIL bill with a few CompuServe accounts for key volunteers without other Internet access, at an estimated savings of more than $20,000 per year. Everybody else had to provide their own Internet access.
This was a year before the release of Mosaic, the first graphical browser for a new thing called the World Wide Web. Email was the main thing. FTP was a workhorse for distributing files and software, but not very nice to use. The internet community was experimenting with ways to do more, but nothing really clicked until the web.
Two years later, at the 1994 Space Symposium in Orlando, Paul made a presentation to the AMSAT Board about the World Wide Web. From the minutes of that Board meeting:
He told about a powerful extension of the Internet called the “World-Wide Web” that is capable of interfacing with sources including not only text, but photos, movies, audio and hypertext documents. This can serve as an on-demand magazine or as a library. As such, it could be used to provide a source for AMSAT archival material. He offered to establish such a capability and make it available to AMSAT at no cost to the organization. The Board accepted this offer with thanks.
The Board also allocated funds for a hardware upgrade to a more powerful PC-based platform with more disk space. AMSAT President Bill Tynan, W3XO, created a new Electronic Publications department to own the budget item for these funds, and appointed Paul Vice President of that department.
Within a short time, with more help from Brian, the new amsat.org machine was online at UCSD, and serving http://www.amsat.org to a world that was just catching on about the web. Paul built the initial pages by hand, of course, since that was the only way to do it. They were mostly just plain text.
From nearly the beginning, occasional front-page feature articles were published. The first feature article called attention to a series of visible passes of the Russian space station Mir in December, 1994. It’s still available on the web, in its original location. We ventured into multimedia with “Sounds from the First Satellites” by Roy Welch, W0SL, and posted photographs from very early in the Phase 3D development project. The archive of downloadable software grew, alongside the listings of software and other products made available by AMSAT as fundraisers. The goal was to be the preeminent online resource for amateur radio satellites.
Paul envisioned the AMSAT web site as primarily a reference source. People would come to the site to find specific information. They would probably already know something about AMSAT and amateur satellites. Casual walk-in traffic wasn’t really expected to be heavy. News coverage was left to the AMSAT News Service. ANS bulletins were of course available on the web site, but the front page wasn’t news-oriented at all. Only major events of lasting interest to AMSAT would get any headlines on the front page. This kind of semi-static site design was increasingly out of sync with the dotcom-era web.
The 1994 web design evolved gradually over nine years. It got a lot bigger, and many new features were added. The basic design, however, remained pretty much the same: a hierarchy of text-based links rooted in a text-heavy, mostly static front page. It was overflowing with information, some fresh and some stale, and its hierarchy was getting difficult to navigate. The aesthetic design of the site was dated.
At the beginning of 2004 Emily Clarke (now N1DID, then W0EEC) undertook a complete redesign of the site. The new design was announced to AMSAT-BB (as a beta test) on June 22, 2004.
 For example, http://www.amsat.org/amsat/features/scope/scope.html
 The last version, more or less, is still visible at http://www.amsat.org/amsat/AmsatHomeOld.html
I finished installing a VHF/UHF amateur radio transceiver in the BMW Z4 today. The radio is a Yaesu FT-90, one of the smallest mobile transceivers around. The main unit is installed in the trunk, hanging from the hinge bracket near the right fender. The front panel stashes nicely in place of the ashtray. The microphone cable comes out on the passenger side of the center console, so the mic can be stowed in the cargo net there when not in use. The trickiest part was finding a satisfactory place for the speaker. I ended up mounting it behind the driver’s seat, as shown below. This means the seat won’t go back all the way, but my legs are short so that’s not usually an issue.
I just noticed that it was exactly one year ago today that I installed an antenna on the K1200LT motorcycle. There still isn’t a radio installed on the bike, though. I originally bought the FT-90 that went into the Z4 for the K1200LT, but I eventually decided it was the wrong radio for the bike. It can’t be operated without the extra buttons on the special microphone, and the hand-held microphone would be replaced by a helmet headset on the bike. Perhaps I will eventually put the Kenwood TS-942 from the RX-7 on the bike. Maybe by this time next year.