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

jmfranke jmfranke at cox.net
Sat Jul 6 14:19:12 EDT 2013



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From: "jmfranke" <jmfranke at cox.net>
Sent: Saturday, July 06, 2013 2:09 PM
To: <time-nuts at febo.com>
Subject: Re: [time-nuts] Speaking of Costas loops (WAAS)

> A lot of the changes from "bent pipe" to the new system including C-band 
> uplink is explained here:
>
> http://www.insidegnss.com/node/697
>
>
> While there, downlink the extended PDF version.
>
> John  WA4WDL
> --------------------------------------------------
> From: "Magnus Danielson" <magnus at rubidium.dyndns.org>
> Sent: Saturday, July 06, 2013 12:57 PM
> To: <time-nuts at febo.com>
> Subject: Re: [time-nuts] Speaking of Costas loops (WAAS)
>
>> On 07/06/2013 06:29 PM, Joseph Gwinn wrote:
>>>>> 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).
>>>>
>>>>
>>>> This is interesting. Does it imply that they regenerate the code on 
>>>> board?
>>>
>>> Very unlikely, because then the bird would have to understand every
>>> possible code, including those not invented when the bird was launched.
>>
>> If it is within the Gold codes being used for GPS and WAAS, they only 
>> need to alter the 10 bit reset-value of the G2 PRN code. See the WAAS 
>> specification, as this method is being recommended for receivers.
>>
>> Within that limit, it is relatively cheap to provide code tunability.
>>
>> Cheers,
>> Magnus
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