Thanks to everyone who replied. There seem to be enough questions that I am going to provide more detail on the projects.
Two boys, Joshua Fournier, KI6PJW (Gen), and Michael Binon, KI6QOC (Tech), set out to build a totally-self-contained portable HF station that is small enough to fit into a backpack and still allow them to carry necessities for survival. Michael is in sixth-grade and a Boy Scout well on his way toward earning his Eagle Scout rating. He and Josh both like to hike so decided that it would be cool to take the radio with them. The goal was to have it be completely self-contained and provide its own power regardless of the duration of the hike, hence the desire for solar power to keep the battery charged. Last year I had students who tried to do projects together which did not work out. One student ended up doing most of the work and the results were clearly not a team effort. This year I told them that they could not collaborate and must each produce an individual project. That way one student's failure to perform would not impact another student. Since both Michael and Joshua had an interest in constructing the backpack station, I suggested that they define it as two separate engineering problems to solve and then each could solve their own particular problem independent of the other. Joshua took on the problem of the power system and physical design while Michael tackled the problem of selecting the best antenna to go in the backpack. Joshua's problem was pretty straight-forward: 1. do a power budget to determine required battery capacity; 2. select an appropriate battery technology (LiPoly, NiMH, or lead-acid); 3. determine necessary PV panel size; 4. come up with a rugged, adjustable mounting for the PV panel that would allow room for the rest of the stuff in the backpack, e.g. sleeping bag, tent, food, water, etc. Joshua even provided a fall-back position on the antenna by building and testing a center-fed, non-resonant doublet fed with 300-ohm twin-lead and tuned with a small, balanced-line tuner. Josh did some serious engineering. He would come up with ideas, sketch them in his engineering notebook, bounce his ideas off of me, research materials, and then go build. He got his father and grandfather to help with metal fabrication. I wish that some of the engineers that I once had working for me did work of this quality. Michael discovered about half-way into his project that antennas are a much more difficult topic than he originally anticipated. He had some real false starts and darned near broke up his parents' marriage getting his father, who knows nothing about radio, to help. I had to take a more proactive role and guide him through understanding the various antenna types and their construction. His original plan was to build 1/10th scale model antennas at 2M and test those as neither he nor I had come up with a way to test antennas in real-time with the same signal. Instead we were going to use my miniVNA to measure path-loss in the far-field. Being able to quickly build and test scale antennas gave him a much better understanding of what was happening. It also left our technology lab at school looking like a spider web with students having to crawl on the floor to get to open workspace. :-) About that time I was talking about multiple receivers in the F5K vs. the K3. We were talking about diversity reception and a light bulb went on for me. I suggested to Michael that he use the F5K to measure two antennas simultaneously. He came up with a test plan using the dipole as the reference antenna against which to test each of the other antennas; i.e. 1-wave delta loop, 1/4-wave ground plane, and end-fed non-resonant wire. Michael drew up a layout for the antennas which would minimize interaction and collected materials. The head administrator for the school gave him leave to use his classmates and class time to set up his antenna test range as a practice run setting up antennas for field-day. (Field Day at our school is an official school event.) Nothing went according to plan. Everything took three times longer than planned and Michael only managed to get his data last weekend. Still, it was good data. He used PSK31 signals as his test signals because they are narrow, constant power, and all the power is concentrated close in to the carrier allowing narrow filters to minimize power from adjacent signals and to provide good S:N. The only problem was, last weekend was a big PSK31 contest and it took real skill to collect data points with the quick exchanges. OTOH it also meant that there were a lot of stations on the air so he didn't lack for sources. When we got done (yeah, I got roped into running the F5K and calling out signal-level readings) we had quite a bit of data. Because of the 1dBm resolution Michael took many readings and then averaged the differences. I was surprised at the accuracy of the results. His data showed that the loop had a 2.6dB advantage over the dipole; the ground-plane had 0dB advantage over the dipole, and the end-fed wire with counterpoise came in well behind the dipole, -15dB. After taking data for the dipole and loop and seeing the loop's consistent 2-3 dB advantage, he became concerned about the data from the dipole and ground plane with no apparent consistency. I had him put on the headphones and listen to signals in diversity mode. Understanding led to a discussion of polarization rotation. We took lots of data points and averaged the data. This time the average indicated that there was no advantage to the ground-plane over the dipole. The end-fed wire was a big loser. Its only saving grace was that it was the easiest antenna to build and erect so it actually didn't end up too far down on his comparison matrix. Now it is possible to glean this information from the various ARRL handbooks but the act of doing the work and getting good data in the field both aids in building understanding and confidence. When Josh and Michael talk about antennas they now sound like old hams. Turns out that Michael and Josh were their own competition. Michael placed 1st and Joshua placed 2nd in the engineering category. If I had a choice I would have reversed those because this is Joshua's last year (we only go to 8th grade) and he really did his project 100% independently. Michael is only in 6th grade so has several years to compete in the Junior division. Also Michael needed more help and direction. Regardless, he did the actual work, does understand the material, and could certainly replicate it completely on his own without assistance now so I think he earned the award. Moving on, I had several low-end 434MHz part-15 transmitter and receiver modules intended for wireless remote control kicking around for the kids to use in projects. I originally got them to use in making hidden transmitters to t-hunting and also to send up in balloons as balloon-sats for tracking and simple telemetry. I figured we could afford to lose the $8 100mW transmitter modules. The $8 receiver modules are superregen but they work and I am again unconcerned about something happening to them. Frankie, KI6QYS, looking for something to do that involved some kind of remote control, latched onto the modules. He has written simple programs to control the robots but this became a crash-course in learning about async serial communications. I gave him a plan working up from simple 4-line programs keying the transmitter and detecting that at the receiver, to sending data from a PC, framing it, and displaying it on a small LCD at the receiver. Again, nothing went as planned and I spent a fair amount of time giving him small experiments to try to determine what was happening. We ran into all kinds of limitations with the small modules and with the Basic Stamp microcontrollers which ended up reflected in the final code. (The final framing has the transmitter sending pad characters to deal with timing constraints in the receiver code.) Regardless, he finally converged on code that would allow reliable transmission of arbitrary-length messages from one microcontroller to the other. It isn't quite AX.25 or TCP/IP but he understands what he did and what all the problems were. He even asked me about how to do a preamble that wasn't characters so it shows he is thinking. Next I probably need to show him how HDLC is framed. Not bad for a 6th-grader who started out thinking that this science fair stuff was boring and not worth doing. The key to me is that these were real engineering projects with real goals. Every single project presented serious problems that required creative problem-solving. All students went from almost zero knowledge to being able to troubleshoot problems effectively which indicates significant understanding. You can't ask for more than that. It is also somewhat serendipitous to me in that I won the regional and California State science fairs two years running back in the 1960's. It will be interesting to return to the place where I won 42 years later with my own students in tow. 73 de Brian, WB6RQN/J79BPL _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flex-radio.com/ Homepage: http://www.flex-radio.com/
