[time-nuts] Speaking of Costas loops

Dennis Ferguson dennis.c.ferguson at gmail.com
Thu Jul 4 23:16:24 EDT 2013


On 3 Jul, 2013, at 21:05 , Bob Camp <lists at rtty.us> wrote:
> If the WAAS sats were purpose designed to provide a high accuracy carrier, then yes there are ways to do it. The fundamental design concept of a "bent pipe" is that you don't do any of that. You do not care what's going through the bird, it just maps the input frequencies to the output and amplifies them (a lot). Again, the WAAS signal is simply piggybacking on existing hardware. The conversion oscillator is not locked to the GPS carrier (or to any other carrier). It's simply a free running quartz based oscillator, running into a synthesizer to get the appropriate microwave frequency. 

I'm not sure about the "Again, ..." part.  All three WAAS satellites are commercial
satellites but they were all launched recently enough (2 in 2005, 1 in 2008) to have
had WAAS-specific payload added.  The solicitation for the 2008 satellite is here

   <https://www.fbo.gov/index?s=opportunity&mode=form&id=f5aacd4bba2ef67b0c59b586900499b6&tab=core&_cview=1>

and is dated 2002; this isn't looking for service on a satellite already in orbit.  For
the 2005 satellites, the Telesat one is mentioned here

   http://www.telesat.com/services/government-services

which says

    Telesat’s Anik F1R includes a specialized payload for the Wide Area Augmentation
    System

while you look at the Orbital Sciences blurb on the last three satellites it built for
PanAmSat, here

   http://www.orbital.com/newsinfo/publications/galaxy_fact.pdf

you'll see that they are all exclusively satellite TV things, with 24 active
C-band transponders and 8 spares, except for Galaxy 15 which weighs 350 pounds
more than the other two and about which it says:

    The Galaxy 15 satellite, which features a unique hybrid payload
    configuration, was launched on October 13, 2005. In addition to C-band
    commercial communications, the spacecraft also broadcasts Global
    Positioning System (GPS) navigation data using L-band frequencies as
    part of the Geostationary Communications and Control Segment (GCCS)
    implemented by Lockheed Martin for the U.S. Federal Aviation
    Administration (FAA).

I don't think they can use any old satellite for WAAS, they added payload
for it.  Note that when Galaxy 15 went awol it took the WAAS service with it
for most of a year even though it was replaced in its orbital slot for TV service
by a spare within a week or so (though Wikipedia says the replacement was Galaxy 12
so I guess that's predictable from the blurb above).

So I've been assuming that while the WAAS satellites are commercial the WAAS
transmitters are specialized to the service and included for its exclusive use.
I hence guess they could have been designed to work however they needed to.

Dennis Ferguson


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