On 7/6/13 7:23 PM, Bob Camp wrote:
Hi
Ok, lets *assume* there is some uber secret gizmo in the sat that makes the
unsupervised signal absolutely perfect when transmitted from the sat.
The sat still moves relative to the ground. It's speed is a vector in three
dimensions (up / down , north / south, east / west). Depending on your location
relative to the sat, the doppler will be different.
A cheap GPSDO will give you 1x10^-11 all day long, pretty much forever. It'll
do much better over long time spans. At 1.5 GHz, that would be 0.015 Hz.
If doppler is in the 50 to 100 Hz range, you need to cancel it by > 1000:1
simply to get the carrier as good as a simple GPSDO. That's going to require
accurate position data on the sat, it's velocity (all real time), and your
location.
-----------------
Next you need data on the rest of the constellation. They fly in the same space
as the WAAS birds, and transmit on the same frequencies. As they pass within
the capture area of your antenna you will need a way to figure out which is the
GPS and which is the WAAS sat.
The easy way to do that would be to run a GPS to get all the data and then
process it…..
----------------
Dish costs something
Downconverter costs something
Signal processing the received signal costs something
You still need a GPS
You still need a good local OCXO as a flywheel
It's going to be tough to convince me that's any cheaper than a GPSDO
I think you're right..
But time-nuts don't always go for the "easy" way..
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