[time-nuts] Need advice for multilateration setup

Jim Lux jimlux at earthlink.net
Mon Apr 6 09:13:06 EDT 2015


On 4/6/15 2:21 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.


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.




>
> 			Attila Kinali
>




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