Luis Cupido wrote:
Hi,
The fact they refer that atmospheric s/n degradation and dropouts etc
being replayed precisely lead me to think this is just a spectrum
rec/play machine (no mod/demod of any kind)
like the ham-oriented "time machine" but for GPS.
http://www.expandedspectrumsystems.com/prod2.html
Luis Cupido.
ct1dmk.
But they mention software to generate sequences. It's actually a fairly
clever idea. It's easy to stream 16.3xx Mbps from a modern computer, so
you could generate an arbitarily complex signal off line..
For a lot of applications this would be great. A nice test source that
you could replay on command.
The only question I'd have is whether the 1 bit DAC can adequately
represent the real-life complex signal. I suppose, intuitively, since
your receiver is digitizing it with a 1 bit ADC...
And, I have a question whether the 1 bit DAC can produce a high enough
fidelity waveform for a higher performance receiver that uses a multibit
digitizer.
Since the clock you are recording and playing back with isn't
necessarily as good as the one on the satellite, you probably couldn't
use this for testing your precision receiver. It would be like
introducing a random propagation variation or coax length variation in
the system.
It is intriguing though.. a homebrew version could be quite simple.. you
can get the USB interface and a small FPGA pretty easily. One of those
10.23 MHz crystals from Rick might be handy...
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