[time-nuts] GPS simulator,

Luis Cupido cupido at mail.ua.pt
Fri Nov 26 16:02:29 UTC 2010


 > But they mention software to generate sequences.

Hummm... right...
so I think we need to look inside one to be sure what it is...

lc
ct1dmk.


jimlux wrote:
> 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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