Data collected with a sound card located in Besançon, France,
monitoring DCF77 emission from Mainflingen (Germany). The first measurement
is the frequency offset to cancel the frequency offset between the sound
card local oscillator and the signal received at 77500 Hz. The bottom graph
is the time delay between a GPS (U-Blox) 1-PPS output and DCF77 phase
modulation cross correlation maximum.<br>

<pre>
set xdata time
set timefmt "%s"
set xtics 5356800
set format x "%D" 
set yrange [.7:1.0]
set xrange [1477677970:]
set xlabel 'time (date)'
set ylabel 'freq offset (Hz)'
pl 'df' u 1:2 w d t 'freq. offset'
</pre>

<img src="df.png"><br>

Dataset: <a href="df">file</a> with time (seconds since 1/1/1970 as 1st column,
data as second column)

<hr>
<pre>
set xdata time
set timefmt "%s"
set xtics 5356800
set format x "%D" 
set yrange [-150:700]
set xrange [1477677970:]
set xlabel 'time (date)'
set ylabel 'time offset DCF77-GPS (us)'
pl 'moyenne4' u 1:(($2<0?$2+192000/59:$2)/(192000/59)*1e6-103000) w d t 'GPS 1 PPS - DCF77'
</pre>

<img src="moyenne4.png"><br>

Dataset: <a href="moyenne4">file</a> with time (seconds since 1/1/1970 as 
1st column, data as second column)