[time-nuts] WWV receivers?
jimlux at earthlink.net
Sat Oct 29 12:35:25 EDT 2016
On 10/29/16 4:49 AM, Attila Kinali wrote:
> On Fri, 28 Oct 2016 23:01:52 -0700
> Hal Murray <hmurray at megapathdsl.net> wrote:
>> nsayer at kfu.com said:
>>> That single-chip version is going to have a *LOT* less (and less variable)
>>> latency than an SDR.
>> Latency isn't an issue as long as it is known so that you can correct for it.
>> Has anybody measured the jitter through SDR and/or tried to reduce it? I'd
>> expect that even if you counted cycles and such there would still be jitter
>> from not being able to reproduce cache misses and interrupts.
> Should not be too high. If Jeff Sherman's and Robert Jörden's paper
> is any indication, then the jitter should be dominated by the jitter
> of the ADC and its reference oscillator. So sub-ps, order of 100fs jitter
> should be possible with proper design. Long term drift is another issue
> and I have not completely figured out what are the contributors there.
> Temperature stabilizing for sure helps, but it doesn't seem to be the
> only effect.
Well, that's "jitter in the original samples" which can be very low, as
you describe. But I would interpret the original question as "jitter
*through* an SDR" which implies that we're looking at the timing of
output vs input.
Consider an SDR which receives a RF signal that's BPSK modulated, and
puts out a stream of data bits on a wire (as opposed to dumping into a
file or network connection)- and you want to look at an eye diagram of
> Attila Kinali
>  "Oscillator metrology with software defined radio",
> by Jeff Sherman and Robert Jörden, 2016
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