[time-nuts] iGPS?

David I. Emery die at dieconsulting.com
Tue May 19 01:57:20 EDT 2015


On Mon, May 18, 2015 at 09:52:03PM -0700, Jim Lux wrote:

> Why iridium?  Why not Sirius or XM or DBS. Unless you want something 
> world wide, as opposed to "populated areas served by broadcast radio and 
> TV"

	Well it seems to me I remember Iridium is time domain duplex
around 1610 MHz or thereabouts... which isn't too far from the L1
civilian GPS at 1575.42 and quite possibly inside the bandwidth of
some civilian L1 LNAs and antennas.

	Sirius XM is not that close at 2320-2345 Mhz.

	And inside its spot beam the Iridium signal is quite a bit more
powerful and coming at one from constantly changing angles... whilst 
the Sirius XM birds are either geosync or in Molninya orbits and don't
move much over short intervals - as does an Iridium signal.

	And of course (for the military especially) it IS worldwide and
not just restricted to NA (where such an anti-jam capability is less 
useful at least at the moment).  Something that works world wide
is of course what the military folks need.

	And I suspect timing can be derived from the satellites TDD
and message timing pretty easily if that is accurately synced to some
reference...

	Others more familiar with the details may comment here...

-- 
  Dave Emery N1PRE/AE, die at dieconsulting.com  DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."



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