[time-nuts] Need advice for multilateration setup

Magnus Danielson magnus at rubidium.dyndns.org
Tue Apr 7 14:33:22 EDT 2015


Hi,

On 04/07/2015 02:08 PM, Attila Kinali wrote:
> On Mon, 06 Apr 2015 23:02:01 +0200
> Magnus Danielson <magnus at rubidium.dyndns.org> wrote:
>
>> 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.
>
> Yes. But I would do carrier phase tracking only after code phase
> tracking proved to be not accurate enough. Improving later and
> switching to another band is relatively easy, once you've proven
> that the system in principle works.

One might look at the available frequencies and see if there is a 
telemetry band available which allows wider bandwidth. For the 
application, I don't see that very much transmitted power is needed.

There is definitely a benefit in locking up the carrier and chipping 
rate, preferably so that there is an integer number of carrier cycles 
per chip.

For those unused to the terminology, a "chip" is a single 0 or 1 out of 
the pseudo-random generator. It's encoded as +1 or -1 before being mixed 
with the carrier, thus forming an BPSK signal.

There is a gain for the receiver if the transmitter has the carrier and 
code synchronized to each other like this.

>> 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.
>
> That's a very good argument for higher chiping rates.

I expect that the launch is a bit challenging for the tracking loop.

Much of these challenges should be relatively easy to simulate, such 
that testing can be done before a the first solder-joint gets soldered.

Cheers,
Magnus



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