On 07/03/14 19:28, Lars Walenius wrote:
Chris, about using one Arduino for two GPSDO controllers:
Even if a microcontroller has lots of capacity I would recommend to use
separate controllers for each oscillator. One of the reasons is what Tom van
Baak said about using only one interrupt to avoid jitter and even if you
trigger both channels from the same PPS and have just one interrupt you will
have a problem that you can´t read two ADC´s at the same time.
Even the HC390 I wouldn´t use for two different oscillators to prevent
crosstalk. Both the processor and HC390 is so cheap it isn´t worth the risk IMO.
Cross-talk typically happens though ground-bounce. Just using separate
chips reduces the effect. May not be much of an issue at ns level, but
below.
Actually I would also recommend to put them in separate boxes even if it is
more work (and I´m lazy ) to get best performance.
Having two GPSDO´s that you can compare is very nice as long as you understand
how they correlate , if that is not what you want to test. Of course you can
also set one or both in hold mode to test them freerunning.
Some telecom rubidiums have fairly noisy output. Steering an OCXO for
clean-up might actually provide the best of both worlds. Holdover of the
rubidiums and phase-noise of the OCXO. In that case, keeping them in the
same box makes sense. The arduino could contribute long-term integrator
memory and possibly do temperature compensation of the OCXO as a
feed-forward approach.
I have thought of connecting the M12 to the Arduino and if someone can help
with code to get the sawtooth correction value into the Arduino and decoded I
would be glad to have it.
I've proposed to some of my local friends here, and we will probably do
something with LPROs. We need to look at what GPS modules there is.
I think sawtooth correction should be added. It's not that hard. One
really wants two serial ports, one for the GPS and one for monitoring.
Cheers,
Magnus
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