[time-nuts] Speaking of Costas loops (WAAS)

Bob Camp lists at rtty.us
Wed Jul 10 23:45:39 UTC 2013


Hi

If the WAAS  birds are run in a fashion that gives a true GPS payload performance, why not assign them a SN 32 or below and use them? 

If the WAAS birds are not in the "right numbers", why bother to set them up and spend the bucks to make them behave like a nav sat? What's the payoff?

Bob

On Jul 10, 2013, at 7:40 PM, "David I. Emery" <die at dieconsulting.com> wrote:

> On Wed, Jul 10, 2013 at 02:42:19PM -0700, J. Forster wrote:
>> David,
>> 
>> While I can easily see how you can do closed loop correctioin for Dopplar
>> from the transmission point for a 'bent pipe' repeater, at any other
>> location that correction would not be valid, because the paths are not
>> parallel.
> 
> 	Sorry for my poor choice of words.   That is precisely what I
> meant by "for an observer on the ground it is necessary to correct for
> the satellite orbit induced doppler".    This is true for ANY observer,
> since it would seem certain that the closed loop correction actually is
> structured and calculated to cause the satellite to radiate a carrier
> (and timing modulation on it) equivalent to what an accurate  local GPS
> satellite reference clock would generate if one was aboard the hosted
> payload rather than on the ground.   Anything else would make no sense
> as it is not incumbent on users to try to figure out ground relative
> timing for some unknown uplink antenna somewhere.   And offsetting
> radiated uplink time and frequency on the ground to make it right on the
> satellite at the output of the bent pipe repeater is very feasible and
> more or less a no brainer.
> 
> 	But if the satellite radiates what a local GPS package would and
> transmits ephmerides defining  its position and motion it could be
> included in a GPS solution and could be used for timing and frequency
> purposes the same as any other GPS satellite subject to whatever degree
> of relative accuracy the bent pipe clock obtains and the degree to which
> the ephemerides in the format transmitted allow an accurate position to
> be determined.
> 
> 	And from what I have read it seems very likely the WAAS birds 
> meet these criteria..
> 
> 
> 
> -- 
>  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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