[time-nuts] Speaking of Costas loops

Dennis Ferguson dennis.c.ferguson at gmail.com
Fri Jul 5 19:55:22 EDT 2013


On 5 Jul, 2013, at 08:33 , Bob Camp <lists at rtty.us> wrote:
> The sat needs to transmit at the GPS frequencies and have an uplink that works exclusively with those frequencies. (or at least that sub band). A "normal" transponder probably would not radiate at the GPS allocation, simply to be a good citizen. I believe the "specialization" is simply a frequency mod to allow WAAS to pass through. There is no mention of a space qualified Cs and / or Rb flying on those birds and no indication that the ground segment is controlling such a payload. If all that *was* present, then including them in the normal navigation solutions would be a "zero cost" next step. 

Addressing the last sentence I found a government WAAS reference
which indicates that the WAAS satellites are indeed interchangeable
with GPS satellites in navigation solutions.  It is is on page 7 of
this

    http://www.gps.gov/technical/ps/2008-WAAS-performance-standard.pdf

where it says

    The WAAS GEO broadcast also provides an additional ranging source
    for improved availability of navigation services. When a WAAS receiver
    is using the corrections and integrity messages broadcast by the GEO,
    only four GPS or GEO satellites are needed, which increases the
    availability of service versus RAIM or RAIM/FDE.

While what is or isn't required in the satellite to support this is
still a mystery it seems like the timing accuracy coming back must
end up being equivalent to a real GPS satellite.  What this is good
for is interesting to think about.

Dennis Ferguson


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