[time-nuts] Speaking of Costas loops

[Bob Camp]

Hi

There are two batches of GPS / WAAS sats up there:

1) The ones with numbers above 100 that are geosync and that only do WAAS

2) The ones with numbers <= 32 that do nav. These are not geosync. 

I believe the only ones with corrected / high stab clocks on board are those in the second group. The stuff in the first group aren't dedicated sats, just leased transponders on conventional multipurpose geosync birds. 

Bob


On Jul 2, 2013, at 5:06 PM, jmfranke at cox.net wrote:

> Valid concerns all. What I am building is a squaring circuit for recovering the carrier from a WAAS GPS satellite. Granted there is still some Doppler and other issues, but the accuracy would not be bad and it just looks like a fun thing to do. Plus, I can use my four foot diameter dish antenna to reduce the number of satellites seen, reduce thermal ground noise, and get some signal gain.
> 
> John  WA4WDL
> 
> ---- "J. Forster" <jfor at quikus.com> wrote: 
>> More on your question:
>> 
>> I'm prettyt sure that just sticking up an antenna and hooking up a simple,
>> phase tracking receiver for GPS will yeild nothing useful, because there
>> are always several birds in view, so you will get a superposition of their
>> signals in the bandpass and each signal will be Dopplar shifted be a
>> different amount- a time-varying amount.
>> 
>> You have to use a complete GPS receiver that can unravel it all.
>> 
>> -John
>> 
>> ================
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>>> Here we go again - the first send didn't seem to get through. This is
>>> the second attempt.
>>> 
>>> This talk of Costas loops reminded me of something I wanted to
>>> investigate some day. I read somewhere a while back about
>>> carrier-phase measurements, and various methods for recovering the
>>> GPS carrier frequencies, including the Costas loop, and something
>>> with carrier-squaring. Nothing I found showed actual examples or
>>> detail of how this is done, only high-order mathematical descriptions.
>>> 
>>> For my needs, I'm more of a frequency-nut - I usually don't care
>>> about getting time info, but I'd like perfect 10 MHz for reference.
>>> Can using only the carriers lead to simple ways to get the same (or
>>> better) frequency stability as a conventional GPSDO, but without the
>>> time and location info, or is it pointless to worry about it, and
>>> just go with full GPS decoding of everything? Or, is carrier-phase
>>> just an enhancement only if you already have the full GPS info?
>>> 
>>> I know that the group could redesign the whole GPS system with tubes
>>> if necessary, considering recent philosophical discussions on that,
>>> so I think there's plenty of knowledge here about carrier-phase
>>> related stuff too.
>>> 
>>> Ed
>>> 
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>> 
>> 
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