[time-nuts] chrony vs ntpd

John Ackermann N8UR jra at febo.com
Sat Oct 28 17:34:56 UTC 2017

Jim, I thought about using an RF-input sync pulse for alignment during 
the Solar Eclipse measurement experiment, but ended up running out of 
time to implement it.  But some very crude experiments indicated that 
it's not hard to generate an edge out of a PPS that creates a comb well 
past HF.  My idea was to do a divide-by-sixty to end up with 
pulse-per-minute rather than PPS.  The lower rate would be less annoying 
to filter out of the results.

I'm interested to hear if you end up doing this, and if so how.


On 10/28/2017 12:04 PM, jimlux wrote:
> Now that I have successfully connected my GPS receiver to my beagle and 
> I'm getting pps ticks into the driver, etc. (thanks to info from several 
> folks on this list!) the question arises of whether to use ntpd or chrony.
> For my particular application, I'm more interested in synchronizing time 
> on the local machine, not necessarily being a NTP server - all of my 
> beagles have a GPS on them.  Of course, there may be times when a GPS 
> doesn't work, or something else comes up where it would be useful for 
> one of the machines to "get time" from somewhere else.
> What I am doing is using the Beagle to capture RF samples (RTL-SDR) in a 
> distributed array, with wireless connections among the nodes.  The 
> processing isn't necessarily real-time (maybe later..), for now, it's 
> "trigger some seconds of capture at approximately the same time" and 
> post process in matlab/octave.
> There's all kinds of nondeterministic latency issues with the 
> USB/RTL-SDR path, so I'm under no illusion that I can capture samples 
> aligned to the 1pps.  However, what I *can* do is generate a "sync 
> pulse" from the 1 pps and feed it into the RTL's RF input in some (TBD) 
> way.
> And the 1pps might give me a clever way to calibrate the frequency drift 
> of the RTLSDR's clock.
> Right now, I'm interested in HF signals (so the period is 30 ns at the 
> top end, and 500 ns at the bottom end)
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