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

[David I. Emery]

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."