Reality intrudes on most engineering projects, and produces a discrepancy between rosy project plans and actual progress. A small example of this showed up in my Rover “Radio Control Link”. This is of course a trivial function with hobby RC systems. But I like to make things difficult.

Actually, I want to use this as a test bed for hardware which I will use in orbiting NanoSat links and in actual GLXP operations near and on the Moon. Finding the real problems now, rather than using a different RC link, one incapable of working at Lunar distances, is actually quite a blessing!

All of my projections for lunar control and communication assume very narrow bandwidth and high gain antennas. High gain antennas are practical only at UHF and microwave frequencies. Standard RC equipment uses much wider communication bandwidth, which requires much more RF power for the same range but makes tuning less critical. Limiting system bandwidth to less than 200Hz at frequencies above 400MHz requires tuning accuracy of about 1/10 part per million. This is far below the accuracy of even pretty good crystal oscillators. For spaceflight, Doppler shifts produce many ppm of frequency shift, so coordinated tuning of the links are necessary to operate in narrow band modes with relatively low RF power. Those systems I have planned and breadboarded for space use.

But attempting to use the same hardware for open loop control (without a coherent – phase locked – return link) was unworkable without modifications. An “Automatic Fine Tuning” system (once a novelty but now common) had to be added to the RC receiver to operate in this mode. That of course takes care of the problem, and gives me an additional circuit option for the Phase Lock portion of the space system. Bit by bit, progress continues.