[time-nuts] Need advice for multilateration setup
magnus at rubidium.dyndns.org
Mon Apr 6 17:02:01 EDT 2015
On 04/06/2015 11:21 AM, Attila Kinali wrote:
> On Sat, 04 Apr 2015 08:49:01 +0200
> Magnus Danielson <magnus at rubidium.se> wrote:
>> 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.
> This shouldn't be much of a problem. Using a chiping rate of a couple
> of kHz should be enough for this application. The signal strength
> can be rather large, directive antennas can be used and the expected
> noise level is rather low. So there no need to use a high chipping
> rate to compensate for noise effects. Of course, using a higher
> chipping rate makes it also easier to get an higher accuracy, but
> I would start with something easy to do first, like a 100mW transmitter
> in the 70cm band with 10kHz chipping rate (or go to a sub-band,
> where 200kHz signals are allowed). With that kind of setup it should
> be possible to use something like RTL-SDR for the first experiments
> and then gradually upgrade to better hardware to improve accuracy.
You want to keep your chip-rate up to make the integer ambiguity of the
carrier phase simple. The carrier frequency divided by chipping rate
ratio indicate how difficult problem it is to solve (GPS L1 C/A code has
1540). The 70 cm band has rather narrow allocations. The 23 cm band
allow for much wide allocations. The benefit of the 70 cm band is
naturally the easy of getting hardware.
Another benefit of a higher chipping rate is that it can allow for a
higher bandwidth, allowing for tighter tracking of the rocket dynamics.
The chipping rate at some code legnth creates the maximum tracking rate,
and some fraction of that is the highest bandwidth tolerable.
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