[time-nuts] Compensating phase differnces in dual frequency GPS receviers?

Attila Kinali 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.

Hmm.. right...

> 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.

				Attila Kinali

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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