http://www.navipedia.net/index.php/WAAS_Signal_Structure
Doppler Shift: The Doppler shift, as perceived by a stationary user, on the
signal broadcast by WAAS GEOs is less than 40 meters per second (?210 Hz at
L1) in the worst case (at the end of life of the GEOs).
Carrier Frequency Stability: The short term stability of the carrier
frequency (square root of the Allan Variance) at the input of the user´s
receiver antenna will be better than 5x10-11 over 1 to 10 seconds, excluding
the effects of the ionosphere and Doppler.
Polarization: The broadcast signal is right-handed circularly polarized. The
ellipticity will be no worse than 2 dB for the angular range of ±9.1o from
boresight.
Code/Carrier Frequency Coherence: The lack of coherence between the
broadcast carrier phase and the code phase shall be limited. The short term
(<10sec) fractional frequency difference between the code phase rate and the
carrier frequency shall be less than 5x10-11 (one sigma). Over the long term
(<100 sec), the difference between the change in the broadcast code phase
(convert to carrier cycles) and the change in the broadcast carrier phase
shall be within one carrier cycle (one sigma).
Correlation Loss: Correlation loss is defined as the ratio of output powers
from a perfect correlator for two cases: 1) the actual receiver WAAS signal
correlated against a perfect unfiltered PN reference, or 2) a perfect
unfiltered PN signal normalized to the same total power as the WAAS signal
in case 1. The correlation loss resulting from modulation imperfections and
filtering inside the WAAS satellite payload is less than 1 dB.
John WA4WDL
--------------------------------------------------
From: "Joseph Gwinn" <joegw...@comcast.net>
Sent: Saturday, July 06, 2013 10:50 AM
To: <time-nuts@febo.com>
Subject: Re: [time-nuts] Speaking of Costas loops (WAAS)
Re: time-nuts Digest, Vol 108, Issue 29
On Fri, 05 Jul 2013 19:55:42 -0400, time-nuts-requ...@febo.com wrote:
Message: 6
Date: Sat, 06 Jul 2013 00:27:33 +0200
From: Magnus Danielson <mag...@rubidium.dyndns.org>
To: time-nuts@febo.com
Subject: Re: [time-nuts] Speaking of Costas loops
Message-ID: <51d74855.9090...@rubidium.dyndns.org>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
On 07/05/2013 10:39 PM, Joseph Gwinn wrote:
Re: time-nuts Digest, Vol 108, Issue 28
Message: 2
Date: Fri, 05 Jul 2013 09:18:39 -0700
From: Jim Lux<jim...@earthlink.net>
To: time-nuts@febo.com
Subject: Re: [time-nuts] Speaking of Costas loops
Message-ID:<51d6f1df.9090...@earthlink.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
On 7/5/13 8:44 AM, Bob Stewart wrote:
Wouldn't a Cs or Rb clock in orbit be slow due to relativistic
effects? I'm pretty sure there is a relativistic correction to the
GPS clocks.
Bob - AE6RV
I believe that the original WAAS repurposed transponders intended for
other L-band satellite signals (e.g. Sirius/XM/LightSquared).
As noted earlier in the discussion, the new satellites might have a
specialized payload, which could have a purpose specific coherent
transponder, rather than a linear translator.
If it is purpose specific and single channel, then making it immune to
the local oscillator is straightforward.
I worked on a proposal for the original WAAS system. The WAAS signal
is not a timing signal in the sense that GPS signals from space are
timing signals. WAAS instead sends out a stream of correction data
that allows one to greatly improve the accuracy and reliability of GPS
signals.
So, unless things have changed greatly, the geostationary satellite
that broadcasts the WAAS signal need not have an atomic clock.
This is naturally still true, but we are into the level of "there's a
signal here, what can we use it for?". Doing a much simplified receiver
could serve some well enough, without going the full monty. It's like
taking the color-carrier of analog TV broadcasts.
OK. Given that the birds WAAS uses were built for communications
purposes, not timing purposes, I'g guess that their frequency reference
is a very good quartz unit. I suppose Rubidium is possible, but Cesium
is very unlikely.
Bent-pipe channels do a frequency change to eliminate singing. I
imagine the datasheet for the rentable comm channels will give the
frequency error and stability of the downlink signal.
Joe Gwinn
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