[amsat-bb] Re: SDX transponder timing delay measurements?

[Robert McGwier]

Howard Long wrote:
> Hi Ken
>
>   
>> As a design goal, it would be helpful to the 
>> OD process if the delay could be made consistent 
>> within about +/-5 micro-sec -- i.e., 1500 meters 
>> (smaller is better).  It is also important to
>> quantify the standard deviation to that bias is 
>> since that is also factored into the OD process.
>>     
>
> I may be wrong, but I can't think of a reason why it wouldn't be well under
> this figure. I was thinking more in terms of 100's if not 10's of
> nanoseconds.
>
> The SDX (a) takes a batch of samples, (b) does its processing, then (c)
> outputs the processed batch of samples.
>
> Each of the three parts takes the same amount of time and all three are
> executed in parallel like a production line using DMA for (a) and (c), and
> the DSP CPU for (b). This time is dictated by the CPU's crystal oscillator.
>
> I am guessing any variation would be predominantly from the analog circuitry
> (R's and C's changing value with temperature?), but Bob may have other
> suggestions I hadn't thought of.
>   

Right on the money.  We can learn the variation in these parameters in a 
joint process with determination of the pseudo-ranges.  It is my opinion 
that doing this joint estimation will yield very good results.  I would 
not be surprised in the least if James and/or Stacey had not already 
done this code.  Stacey has worked on a project he calls Ranger (for 
obvious reasons) and I have not yet studied all of the details but I 
know ranging experiments have been done with it.

Bob
N4HY
> 73, Howard G6LVB
>
>
>
>   


-- 
AMSAT VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats,
NJQRP/AMQRP, QRP ARCI, QCWA, FRC. ARRL SDR Wrk Grp Chairman
"You see, wire telegraph is a kind of a very, very long cat.
You pull his tail in New York and his head is meowing in Los
Angeles. Do you understand this? And radio operates exactly
the same way: you send signals here, they receive them there.
The only difference is that there is no cat." - Einstein