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

[jmfranke]

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" <joegwinn at comcast.net>
Sent: Saturday, July 06, 2013 10:50 AM
To: <time-nuts at 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-request at febo.com wrote:
>>
>>
>> Message: 6
>> Date: Sat, 06 Jul 2013 00:27:33 +0200
>> From: Magnus Danielson <magnus at rubidium.dyndns.org>
>> To: time-nuts at febo.com
>> Subject: Re: [time-nuts] Speaking of Costas loops
>> Message-ID: <51D74855.9090805 at 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<jimlux at earthlink.net>
>>>> To: time-nuts at febo.com
>>>> Subject: Re: [time-nuts] Speaking of Costas loops
>>>> Message-ID:<51D6F1DF.9090800 at 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
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to 
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>