yes, for yesterdays measurements 7.435 MHz/V.
But that number changes from measurement to measurement as i'm changing the setup every time to improve SNR (or bring back stuff i've stolen from 40m )
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So, from the first plot, is the calibration factor for cable delay technique ~ 8MHz/Volt?
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Found at least two (minor) problems:
- So far i measured the zero-crossing of the mixer signal and both peak values and modeled the signal using a sine.
For calibration i used the slope of the sine near the zero-crossing.
As the frequency range for pi in shift is about 60MHz the function is almost linear for the range we measure over 24h (~2MHz).
Today i measured the mixer signal in small steps and compared both techniques. The result surprised me a little bit:
it is not a lot of difference in slope but it is surprisingly linear over a range of 40MHz!
- the channel which contains the calibrated VCO monitor signal uses a wrong sign.
The fit is right, but i remembered that i exchanged the BNC to 2-pole LEMO connector some time ago because it had the wrong sign.
However, the frequency tuning curve i measured with the old (wrong) cable.
I used the right sign on my computer but implemented the wrong one in EPICS, so that data was/is wrong. Will change that tomorrow.
This can't explain the problems i had last week as i used Matlab to convert the monitor signal into frequency, not that channel.
Anyway, this is how the data i took last night (19h) looks like using the right slope (see item 1):
so i think once the EPICS channel is fixed we can trust that channel
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