[ntp:questions] Raspberry Pi error in PPM offset

james.peroulas at gmail.com james.peroulas at gmail.com
Tue Aug 27 01:46:33 UTC 2013

On Sunday, August 25, 2013 1:38:02 PM UTC-5, Hans Jørgen Jakobsen wrote:
> Loking at the link I see that they try to do some magic at line 54 of 
> https://github.com/JamesP6000/WsprryPi/blob/master/wspr.cpp
> " #define F_PLLD_CLK   (500000000.0*(1-2.500e-6)) "

That's actually my code so I'm very familiar with it :) I'm hard coding a 2.5ppm offset to compensate for the difference between the measured frequency and the ntp reported frequency. The reason I'm posting is that I'm unhappy with this workaround and has hoping to dig down and eventually find the real problem :)

> https://github.com/JamesP6000/WsprryPi/blob/master/BUILD
> taks about:
>  "Make sure you are using the latest kernel by updating your system. The latest
> kernel includes fixes wich improve NTP ppm measurement accuracy"

Right. The offset used to be 10PPM and by doing an "apt-get dist-upgrade" a few weeks ago the offset became 2.5PPM. So this offset is clearly influenced by the software, I'm just not sure where :(

> Until the next calibration you dont know how valid your curent measurements are. :-)

"A man with one clock knows what time it is. A man with two clocks is never sure." :)


More information about the questions mailing list