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

Bob Camp lists at rtty.us
Thu Jul 11 10:36:47 UTC 2013


Hi

The pseudo random spreading / looks like noise / buried signal thing is the most common way people piggyback low level signals on a bent pipe.

Bob

On Jul 11, 2013, at 12:00 AM, David I. Emery <die at dieconsulting.com> wrote:

> On Wed, Jul 10, 2013 at 07:40:50PM -0400, David I. Emery wrote:
>> 
>> 	But if the satellite radiates what a local GPS package would and
>> transmits ephmerides defining  its position and motion it could be
>> included in a GPS solution and could be used for timing and frequency
>> purposes the same as any other GPS satellite subject to whatever degree
>> of relative accuracy the bent pipe clock obtains and the degree to which
>> the ephemerides in the format transmitted allow an accurate position to
>> be determined.
>> 
>> 	And from what I have read it seems very likely the WAAS birds 
>> meet these criteria..
> 
> 	Thinking some more about the bent pipe repeater aspect of
> WAAS, aside from allowing any kind of WAAS like signal someone might
> invent in the future to be retrofitted to existing satellites without
> a long replacement cycle and expensive launches being involved - there
> are some interesting properties of the design.
> 
> 	One is that one COULD bury in the WAAS uplink cryptographic
> (eg essentially random to users not in possession of the key) spreading
> sequence transmissions that would be radiated globally and could be
> received with "unique" GPS hardware... such a covert channel in civilian
> GPS could have various purposes... and would look rather noise like
> to the rest of the world.
> 
> 
> -- 
>  Dave Emery N1PRE/AE, die at dieconsulting.com  DIE Consulting, Weston, Mass 02493
> "An empty zombie mind with a forlorn barely readable weatherbeaten
> 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
> celebration of what could have been, but wasn't and is not to be now either."
> 
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