I seem to recall a while back that Arecibo was having funding difficulties and was looking for new programs. There is another 'something that shoots straight up' with a little bit of ability to tilt the beam. They have to move the feed around to change pointing angles, no idea if they can track fast enough for a cubesat or what their lateral limits are. I think they can at least track as fast as the moon moves because they've done EME stuff in the past.

using a quick online dish gain calculator, and i know arecibo is spherical not parabolic, (http://www.satsig.net/pointing/antenna-beamwidth-calculator.htm) at 437 MHz, with 50% efficiency and a 300m diameter, your looking at almost 60dB gain on boresight. So 1W at the feed gets you a Megawatt EIRP. The price you pay for that though is a 0.2 degree 3dB beam with probably minimal tracking capability.

could be a neat experiment though to try to time things right with the orbit and give it a go. I'm pretty sure Arecibo is 'ham-friendly' and would probably be open to the idea. I think the folks at Greenbank are similarly 'ham-friendly' because I've heard stories about the use of old systems there (not the 100m telescope that is actively used) for EME as well (maybe a better tracking capability?).

Also, I cant remember clearly, but I think there was a program back in the 60s (maybe 70s?) to deploy little X shaped dipoles into orbit. I think these were designed to resonate at microwave (possibly X-Band) frequencies and the idea was to create a 'cloud' of them and bounce comms off them between ground stations (maybe it was an initial investigation into X-band for satcom work? I can't remember, I think i read it in the history of the DSN or something like that). I bet a cubesat could be a handy little 'deployment mechanism' for something like this (1u's worth of rolled up thin tape measurers or piano wire cut for 70cm, pop the door just like a PPOD and now you've got a cloud of 70cm dipoles). There was a lot of concern even back then about causing significant orbital debris problems, but as predicted the little tiny hair-like X's decayed relatively quickly after a few weeks. If you deployed at a low altitude (maybe 350-400km or less?) I bet you could get past the orbital debris mitigation requirements. Slap a transponder on the thing too, so it can be used while we wait for the orbit to decay low enough for the filament deployment.

Fun mind game.

-Zach, KJ4QLP

Research Associate Ted & Karyn Hume Center for National Security & Technology Virginia Polytechnic Institute & State University Work Phone: 540-231-4174 Cell Phone: 540-808-6305

On 8/8/2016 4:05 PM, 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-ownershi...

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...

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