Multipactor in Low Pressure Gas and in ... - of Richard Udiljak

correspond to huge increases in the decibel scale, which can be seen in
Fig. 6.8.
(dBm)
−60
−65
−70
−75
−80
−85
Noise Power (100 samples noise average)
0 10 20 30 40 50
Time (s)
60 70 80 90 100
Figure 6.8: The same sequence as in Fig. 6.7 (except that in this case the
entire sequence is shown). The small initial steps of Fig. 6.7
become huge steps on the logarithmic scale.
The above examples, which used the new detection method, relied
on close-to-carrier noise measurement data. However, the mechanism
which is utilised requires primarily that the input signal is amplitude
modulated, that the detected signal is proportional to the difference
between the input power and the multipactor threshold and that the
detected signal responds quickly to changes in the multipactor event.
The two first conditions are likely to be fulfilled by all detection methods
for multipactor, but the last will have to be verified for each method.
Results from measurements presented in [14] show that third harmonic
detection is faster than close-to-carrier noise detection, which should
make it excellent for AM detection. In general, probably any method
can be used provided that a suitable AM frequency is chosen and that
the instrument used for detection has a sampling frequency that is more
than two times larger than the modulation frequency in order to fulfil
the Nyquist criterion.
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