Jim,
On 04/06/2015 03:13 PM, Jim Lux wrote:
On 4/6/15 2:21 AM, Attila Kinali wrote:
On Sat, 04 Apr 2015 08:49:01 +0200
Magnus Danielson <mag...@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.
One strategy for this kind of application is to do the "fine
measurement" using carrier phase, and use the PN code to do ambiguity
reduction. Then, a low chip rate is fine: you're basically using it as
a check that you haven't "slipped a cycle".
I would think that the RTL dongles would work just fine, especially if
you radiate a pilot tone from a fixed location as well as the tone from
the rocket. You basically set up two PLLs in software one to track each
tone, and subtract the phase of one from the other for each ground station.
Indeed. Considering that in the start location you can solve integer
ambiguity, especially with a pilot-tone or several radiated. Hacking in
on the RTL-SDR to steer or replace the clock with a more stable clock
might be considered.
Cheers,
Magnus
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