[time-nuts] Compensating phase differnces in dual frequency GPS receviers?
attila at kinali.ch
Fri Dec 2 09:28:57 EST 2011
On Fri, 02 Dec 2011 05:57:35 -0800
Jim Lux <jimlux at earthlink.net> wrote:
> Combs are used all the time for this kind of thing (e.g. calibrating
> Deep Space Network). There's an old paper about calibrating a
> interferometer radio telescope at Stanford using this kind of thing (by
> Bracewell, as I recall)
My google skills fail me on locating this paper. Could you give
me a bit more information? Like the title or the journal it was published in?
> It's easy to distinguish the comb from the GPS signal... the GPS is PN
> coded, the comb is not. If you pick your levels right, depending on
> your digitizing strategy, it might not even jam the GPS, so you could
> leave it on.
> However, even that's not a panacea, because generating and distributing
> that idealized comb is non trivial without destroying the phase
> relationship between the comb "teeth". I guess it really depends on how
> nutty you want to be. 1 nS is pretty easy, I would think. 1pS is a lot
> harder. 1 fS is very hard.
I don't think that sub 100ps is even necessary, as the rest of the
system will be hardly able to get to that resolution (The available ADCs
have <100Msps and too long integration times do not work well in hardware).
But <1ns should be feasible and desirable.
But, what's the problem in distribution of the signal? I would have
(probably naively) feed that into the input LNA.
The trouble with you, Shev, is you don't say anything until you've saved
up a whole truckload of damned heavy brick arguments and then you dump
them all out and never look at the bleeding body mangled beneath the heap
-- Tirin, The Dispossessed, U. Le Guin
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