[amsat-bb] Re: 2.4GHz broadband router on satellite?

Greg D ko6th.greg at gmail.com
Thu Feb 21 21:30:58 PST 2013

Lee Maisel wrote:
> James French wrote:
>> What are the possibilities of building a satellite that uses a Linksys
>> WRT54GL router with a modified DD-wrt or HSMM-Mesh software as a store
>> and forward BBS, to route a received request from one station to another
>> station, or even to connect to a on board networked camera to receive
>> images?
>> What kind of uplink power would be needed from the home station?
>> How fast could the speed(s) get theoretically?
>> How big would the antenna have to be on the craft and for the ground
>> station to even be able to do this adequately?
>> Would the doppler be too much to even consider this?
>> Would the space environment be too harsh for something like this?
>> This is just something I was thinking about this morning and thought I
>> would toss it out.
>> James W8ISS
>> _______________________________________________
> THAT is an AWESOME Idea!
> I don't see why it wouldn't work, I don't know if doppler is an issue 
> though, it may not be if the modulation is FM.
> The antenna would not have to be big, it's 2.4Ghz
> Why don't you post this on the HSMM-MESH.org web forums and get ideas?
> 73
> Lee
Hi James, Lee,

If you are thinking of using standard Wi-Fi as the link protocol, be 
aware that the timers that drive the protocol don't well work over long 
distances (few miles).  Something about the speed of light not being 
fast enough.  Real bummer.  These would need to be adjusted, though I 
think the implications for a point-point connection may not be too severe.

Besides doppler shift, which could be a problem depending on how agile 
the ground station is, the modulation scheme (it's NOT simply FM) uses 
about 20 mhz of bandwidth, so you will need significant power to get the 
20db S/N needed to decode anything halfway reliably.  Remember, a 
typical AP runs 100mw on 2.4 ghz, and gets reliable communication over 
distances of 100's of FEET with omni antennas.  Add some gain on both 
ends (so now you need attitude control on the satellite!), and you can 
go a few miles.  But 100's of miles to orbit?  I need someone to "do the 
numbers", but I bet it's not too good.

Greg  KO6TH

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