[time-nuts] Need advice for multilateration setup
magnus at rubidium.se
Sat Apr 4 02:49:01 EDT 2015
We essentially propose that you mimic the GPS system.
The original GPS birds are relatively stupid.
In GPS, the core clock produces 10,23 Mhz (modern GPS rubidiums output a
different frequency, but that is not the point here), for C/A code it is
divided down with 10 to produce the C/A chipping rate of 1,023 MHz and
considering that the Gould-codes being used is 1023 chips long, they
will wrap around every 1 ms. The same 10,23 MHz is then used to produce
the carrier frequency which is 154 * 10,23 MHz. The produced PRN
sequence alternate between +1 and -1 and when mixing this with the
carrier frequency a BPSK signal is produced which is amplified and
transmitted. A second carrier is also produced as 120 * 10,23 MHz.
This is on either side of the amateur 23 cm band. That's also the first
band where you have bandwidth enough to fool around with stuff like this
without breaking the bandplan.
On 04/04/2015 05:12 AM, Robert Watzlavick wrote:
> I have an amateur radio license (mostly CW/HF and some VHF/UHF
> experience) and I've written some driver software for an IQ demodulation
> board but I have to admit, I would have no idea how to begin setting up
> that system as initially described by Attila and expanded by you and
> others. I have a rudimentary understanding of the modulation schemes
> involved but I don't fully understand how the various codes mentioned
> fit in. I've poked around a bit at some articles on PN codes and I can
> see how data would be transmitted but I think I'm missing something key
> that allows you to extract positions, velocities, etc. out of the
> various links. I think I have some more reading to do :)
> On 04/03/2015 06:08 AM, Magnus Danielson wrote:
>> I think this is a good idea, and it is relatively straight-forward to do.
>> You can observe both code and carrier phase this way, given that the
>> transmitting radio is coherent with the code generation clock. Doppler
>> also pops out of the tracking station.
>> A good coding-gain reduces the need for a strong transmitter.
>> The issue might be the allowed width of the signal being transmitted,
>> forcing the chipping rate down.
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