[time-nuts] how good an oscillator do you need for a GPS simulator

Magnus Danielson magnus at rubidium.dyndns.org
Sat Dec 17 14:18:25 UTC 2011


On 12/17/2011 02:37 PM, Azelio Boriani wrote:
> Jim, you're right a DAC is not needed: I was thinking of generating the
> BPSK by a DAC but it is not necessary. I have seen some BPSK hardware
> modulators: easier than generating samples and feeding a DAC.

For a single bird a digital output could be made to work, but for a 
constellation you would need individual bits which would then be mixed 
together using a resistor network since the birds will not have the same 
information due to different PN-cods, same rate since they will have 
different doppler rates etc. etc. Having a three or four bit DAC would 
be an alternative. Also, the square carrier waves would require more 
filtering than what a few-bit sine would require.

So, saving a DAC is not necesserilly as smart as it looks.

Looks like there is room for a GPS/GNSS receiver and simulator list.

Cheers,
Magnus



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