Why did you even do it?

Persistence

There have been a lot of people who have criticized me for staying with this project for so long.  People have asked, "Why did you advertise your failures to the world?"  In the beginning, the World Wide Web was a place where people could share information on interesting technical projects they were doing.  Now, people see it as just a gigantic shopping mall.  It's not my intent to "advertise" anything, but many in the consumer-oriented rocketry crowd see it that way.  I can't tell you how many people have emailed and told me they learned something from the DARTS site.

One reason people do this simply sociological: there are people who ALWAYS 'humbug' anyone doing anything new and different. Mr. Roosevelt said it best:

"It is not the critic who counts; not the man who points out where the strong man stumbled or where the doer of deeds could have done them better. The credit belongs to the man who is actually in the arena, whose face is marred with dust and sweat and blood. At best, he knows the triumph of high achievement; if he fails, at least he fails while daring greatly, so that his place shall never be with those cold and timid souls who knew neither victory nor defeat."

Theodore Roosevelt

"The greater the difficulty, the more glory in surmounting it. Skillful pilots [captains] gain their reputation from storms and tempests."

Epicurus, Greek philosopher

A very good question.  It think the answer boils down to two points:

1. Contributions to the experimenter community:  DARTS expands the bounds of what amateur radio experimenters can do, with frequencies and design  concepts that are at the very edge of the experimental envelope.  Also, such a capability does not exist within the mainstream of amateur (sport) rocketry, so DARTS represents the leading edge in experimental technologies in that field, too.
2. Technical Challenge / Notoriety:  Alright, I admit to being proud of what I and my team members have done, our successes and what we've learned from our failures.  I originally took up this project back in 1989 because it represented a high technical challenge to me then.  Even after I have learned so much and come so far, it still contains significant technical challenge and opportunity for creative expression.

Advancing the State of the Art

One would think by now that there would be a system on the market that does this.  Where are these systems?  I suspect people have tried, and like me, discovered that it costs too much to develop with darned little financial return.

Digital recording altimeters are all the rage, but they have their problems, too:

1. You crash the rocket, you lose your data. It's that simple.
2. No velocity or acceleration data.
3. Only vertical coordinates, so you have no idea what the altitude "could have been" if the rocket hadn't tilted at launch.

What about GPS?  Civilian GPS units are intentionally crippled for high-altitude, high-speed operation--they simply stop working.  See the GPS info on APRS.NET.  For low altitude rockets, I'm sure this would work.  But-- it doesn't have the "cool" factor that a tracking dish has!

I'm convinced that sport rocketeers, by and large, simply don't know what the technology is capable of.  Most sport rockeers think that ground recovery is all they can hope for.  Others think flight tracking equipment would be so expensive that they don't dare ask for it, setting instead for ground recovery only.

Sometimes "old technology" is all that's required to challenge the state of the art.  For instance, if a radar system were built with an angular accuracy of about +/- 0.5 degree, it would be much better than the accuracy of any optical tracking means now emplyed in amateur rocketry.

Some people have asked, "Is a three station doppler tracking system is more expensive than a single angle-tracking base station?"  Most definitely.  I've been down that road, taking my cues from Bjork's work for in the NASA Trailblazer project in the early sixties (see my History page).  First, you must have THREE nearly-duplicate stations which still have to keep their antennas pointed to some degree of accuracy, if any reasonable antenna gain is to be realized.  Further, the intercommunication and station coordination issues are very difficult for a three-station real-time trilateration setup.  And, Bjork's work showed that you really need FOUR stations to subtract out the apparent doppler shift due to error in transmitter frequency.

The Technical Challenge

Some people who ask this question have had (sad) experience with using 5.7 GHz wireless LANs (local-area computer networks) indoors. One reason they don't propogate well in indoor settings is all the metal and water-containing materials in a typical building! (I think most of this was due to phase variance of the chipped direct spread-spectrum signal.)

5 GHz signals do pass well through thin fiberglass, paper, and phenolic.  Loss depends not only on the properties of the materials, but also on the thickness.  A thin material is desirable for airframes, and also desirable from a transmission standpoint. I don't have actual numbers for the amount of loss, but I have put thin phenolic and paper (cardboard) in the microwave oven (2 GHz), and neither absorbs enough energy to get hot.  I don't have any 5.7 GHz data on fiberglass, but the radar guys tell me that you can receive 3.5 GHz signals through a fiberglass radome.   From my testing, I can find no significant attenuation from either plastic nose cones or fiberglass body tubes.
 

Building Your Own Tracking Radar

You _could_ build a 10 GHz "police" Doppler radar kit (Ramsey Electronics, www.ramsey.com I think), but I take it that isn't the direction you're going. You _could_ buy a surplus military radar unit, but in many ways that would be more confusing than developing your own, since much of that technology is so dated.  Also, they are _huge_, heavy, and mostly use 3-phase 440 Hz power (where do you get that?).

There are _no_ kits for real tracking radars anywhere in the world, as far as I can tell.  Heck, there weren't even decent microwave semiconductor components commonly available until recently.

My advice, such that it is, is to read _everything_ you can get your hands on, and to experiment. Read in all electronics disciplines, but especially in radar, antennas, signal processing, analog, digital, and RF electronics.  (Check out my Radar Resources page for some ideas) Read up on control systems, and mechanical engineering.

Learn from the people who've done similar things.  Read all the stuff on my web site.  Read W1GHZ/N1BWT's web site, ESPECIALLY the Online Antenna Handbook.  Read _ALL_ the Microwave Updates from the ARRL, cover-to-cover.

Learn _everything_ you can about radio electronics. Get an amateur radio license, if you don't have one.  Start experimenting with microwave radio. Join North Texas Microwave Society and one of the ham VHF Societies.  Put together some microwave kits from Downeast Microwave (www.downeastmicrowave.com).  Read and understand everything in the HP RF and Mini Circuits data books.

And did I mention antennas?  Get some antenna software (like MiniNEC from www.arrl.org) and start experimenting with antennas.  You _must_ get a copy of Savatini's "Microstrip Antennas for Wireless Applications", because antenna design software comes with the book (only $90!)

Oh, yeah, DSP.  Buy a DSP demo board from Texas Instruments or ADI and write some signal processing programs.  Learn all the DSP algorithms you can, from control systems, to filters, to radio receivers in software.  You'll need 'em. Learn C if you don't know it.

Also, learn metal-working skills.  Learn to operate a drill press, a gas or electric welder and a Dremel tool.  Learn to measure twice, drill straight and cut true.  Heaven knows I've had to learn those lessons more than once.

This quest t has brought me sweat, tears, and delicate, hand-built electronics driven into the ground by runaway rockets! I couldn't even begin to count the money and time I have poured into my search for the tracking radar grail.

Career Advancement?

• My first board I build for DARTS was a digital signal processor.  I learned how to write software for it in assembly language.  So, at work, they started looking for someone who had DSP experience, and could write a real-time pattern synthesizer for a Navy radar simulator.  I raised my hand ;-)  On DARTS, and on this radar simulator, we used Analog Devices DSPs. I used a little-known side effect of the floating-point normalize instruction to count bits in the radar data stream.  I had learned that, you guessed it, on DARTS.
• I completed a 1296 MHz synthesizer design (my first PLL ever) for DARTS just MONTHS before I was called on to design a PLL synthesizer at work.
• After studying monopulse radar design for DARTS, my employer (a mil contractor) needed someone to design RF test hardware/software for, you guessed it, a monopulse radar.  When the boss asked who had radar experience, I raised my hand ;-)
• I originally got into PIC programming to control the DARTS transponder.  Now, I have a string of designs behind me, all driven by various permutations of PICs.
• I learned about traveling-wave antennas and built my own for DARTS.  Later, a project at work required an antenna with a downtilt.  I chose a microstrip traveling-wave array, frighteningly close to what I designed for some DARTS experiments.
• I learned assembly of tiny electronic components under a microscope, so I could solder beam-lead PIN diodes into phase-shifter assemblies for a DARTS phased-array experiment.  Now, I design telemetry radios at work, and the prototype assembly is of course done under a microscope, using the steady fingers I trained on DARTS.
• Log-amps (logarithmic amplifiers) used to be a mystery to me, until I built several for various DARTS versions. A receiver on a telemetry radio I'm working on has an RSSI circuit, amazingly similar to those old DARTS log-amps.
• Once, I actually got an engineering job when the owner of the company happened to to be at a rocket launch where I was testing a 5.7 GHz version of DARTS.  He virtually hired me on the spot after looking at the hardware.