Hi,
On 04/07/2015 02:08 PM, Attila Kinali wrote:
On Mon, 06 Apr 2015 23:02:01 +0200
Magnus Danielson <mag...@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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