Dick Jansson-rr wrote:
Tom has an intesting suggestion of the 3x amplifiers/antennas. I have been suggesting this antenna configuration as I just take the P3C hardware and use it! Please help my poor brain understand how this gets the desired RHCP? Is is just the three rotationally oriented antennas?
Dick Jansson
rjansson@cfl.rr.com
Dick -- if you have 3 antennas at 0º,120º and 240º, you can make them be circularly polarized by feeding them the same RF signal, but at relate phases of 0º,120º and 240º (or 0º,-120º and -240º which is equivalent to 0º, 240º and 120º, i.e. swapping any two of the three, to get the opposite sense of circular). This is completely analogous to taking two elements 90º apart and feeding them in phase quadrature.
Of course, since the elements do not have their centers at the same physical point, the polarization purity degrades off-axis.
FYI -- P3A, P3B=AO-10 and P3C=AO-13 all had 2M antennas sticking out the three tips of the star and were fed in just this way. Of course, AO-10's polarization was screwed up when the launcher came up and "bumped" the satellite just after separation. [I did the mathematical simulation of the "half ZL-special" for Karl as we were building P3A. That was back in the minicomputer fortrash-4 era. Because interactive graphics were unknown, the simulation was an inch-thick pile of computer paper.]
My suggestion was that we basically that, if we had 3 amplifiers we could do the 0º/120º/240º phase split at low level, avoiding the "cost" of the inevitable losses in the 3-way power splitter that would be necessary if we did the split at the amplifier output. And we would have simple built-in redundancy too. As Bob pointed out, this might be too complicated for the DSP HELAPS to deal with.
73, Tom