[amsat-bb] Modulating UHF Retro Reflector at RF?

Greg D ko6th.greg at gmail.com
Mon Aug 8 20:42:07 UTC 2016

Woah.  Are you basically suggesting an "RFID thing" at orbital distances?

How many bits could you transmit during the brief transit through the
fence?  RFID is a pretty low data rate scheme, no?

Greg  KO6TH

Robert Bruninga wrote:
> At the SMALLSAT conference there are always presentations on modulating
> optical retroreflectors so very low power passive pspacecraft can still
> communicate telemetry by simply modulating the mirror of a laser reflector.
> Can we do this at RF?  Unfortunately the 218 MHz megawatt radar fence in
> Texas is now shut down... But, now with the amateur radio announcement of
> the return of the HAARP ionosphere transmitters in Alaska, there too is
> another high power CW system.  But it is at HF.
> http://www.arrl.org/news/haarp-facility-to-reopen-in-2017-under-new-ownership
> So what other HUGE power continuous RF emitters are there that transmits
> straight up that could be used by a passivle ON/OFF modulation of a
> resonant dipole in space to convey a few bits of data from a piece of wire
> in space?
> I assume this is a 1/R^4 range equation.  If I do the numbers right, a
> passive dipole only 200 miles up with a 10 megawatts ERP transmitter at 300
> MHz could be detected by a good low noise CW receiver using a 15 dBi
> receive antenna at -128 dBm in a CW bandwidth?  How many dB can this be
> improved with DSP processing?
> Its just a mind game.  A small matchbox size satellite with dipole antenna
> could at least report a few bits of data per pass over the radar beam?
> I think the Airforce is re-building the radar fence but at S band.  At that
> frequency some gain can be added with multi passive dipoles on a cubesat
> size satellite gravity gradient stabilized to keep it pointed down.  If it
> could be made to work, what could we do with it?
> Just thinking...
> Bob, WB4APR
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