[time-nuts] Commercial software defined radio for clock metrology

Bob Camp kb8tq at n1k.org
Sat May 28 07:55:28 EDT 2016


Hi

The normal process with a 10 Hz beat note in a DMTD is to have something like a 6 Hz two
pole high pass and a 15 Hz two pole lowpass after the mixer and before any zero crossing stuff. 
This is after down conversion, but before any demodulation.  This of course is based on the 
fundamental assumption in a DMTD that the inputs are within a fraction of a Hertz of the target
at all times. In a system that has one input offset 12 to 121 Hz and the other at 80 to 9,000 Hz, 
the approach isn’t going to work as well. 

Bob

> On May 27, 2016, at 9:58 PM, Hal Murray <hmurray at megapathdsl.net> wrote:
> 
> 
> bruce.griffiths at xtra.co.nz said:
>> All the filtering and down mixing is done in the digital domain.
>> Anitialiasing filters in front of the ADCs are also be required. 
> 
> What sort of bandwidth is expected?
> 
> The usual trick with audio ADCs is to have a low cost analog filter that 
> does't have a sharp corner but lets everything you want through, sample at a 
> high rate - say 16x, run that through a digital filter with a sharp cutoff, 
> then decimate down to the desired sample rate.
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.



More information about the time-nuts mailing list