Today I did a first real measurement of our living room quartz clock
using a prototype of a GPS/timer/counter.
See photo of the test setup: http://athome.kaashoek.com/time-nuts/clock.JPG
The GPS/timer/counter has a build in GPS with PPS to measure and correct
its internal reference. Nothing special
On the display you can see from left to right at the top settings
related to the three sources of time/frequency:
- Input A, nothing connected, waiting for input
- Input B, where the quartz clock is connected to (DC, 0.8 V trigger
level, 1.8s gate time).
- GPS status
Below the top row you have 3 (can be 1 to 6) numerical data lines
showing data derived from the inputs mentioned above
- Frequency of the quartz clock. As the clock outputs alternating wide
and narrow pulses to drive the coil I had to set the trigger level to
only catch the wide pulse so the frequency is 0.5 Hz
- Instantaneous GPS PPS frequency
- Averaged GPS PPS frequency
And below the data lines you have a graph area where you can graph any
of the data lines. In this case a plot of the measured frequency of the
quartz is shown
The input B is directly connected to the coil of the quartz, no other
signal conditioning is used.
Using the above setup the ADEV of the quartz clock was measured, see:
http://athome.kaashoek.com/time-nuts/Quartz%20clock.png
The measurement of the setup above was labeled with "tinyCount"
I also measured the same quartz clock using a U6200A and a Rb reference,
this is labeled with U6200A
These two measurements seem to be in broad agreement but this may be
just me being overly optimistic.
For people that have worked on atomic clocks or GPS systems this may
look like childsplay and it indeed not very impressive but I am happy
with what I have accomplished.
Erik.
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