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Development and testing of a fast Fourier transform high dynamic-range spectral diagnostics for millimeter wave characterization
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Image of FIG. 1.
FIG. 1.

Noise floor of the frequency measurement system without signal input. The ADC’s maximum input power of is normalized at 0 dB. The measurements are in good agreement with the predictions.

Image of FIG. 2.
FIG. 2.

Flowchart of the LABVIEW application used for data acquisition.

Image of FIG. 3.
FIG. 3.

Left: uncalibrated spectrogram of a measurement without any input signals, showing that 80-sample waveforms are acquired at a rate of 200 kHz, giving spectra with a frequency resolution of 100 MHz. The noise floor is at −63 dBm. Right: detail of the spectrogram, zoomed in at the time interval of 40.00–40.20 ms, showing 40 spectra.

Image of FIG. 4.
FIG. 4.

Left: uncalibrated 320 000-sample spectrogram of a test signal produced with a backward wave oscillator (BWO) at 138.79 GHz. The frequency resolution of the spectra is 25 kHz, while the acquisition rate of the waveforms is 120 Hz, yielding more than 85 dB dynamic range. The figure on the right shows a close-up of the BWO signal, jittering up and down in its frequency band illustrating the high frequency resolution. The 10 MHz frequency range has about 400 frequency bins.

Image of FIG. 5.
FIG. 5.

Hardware calibration curve of the complete frequency measurement system. The high peaks are caused by the dielectric plates in the in-line ECE system. The pink curve is based on the blue conversion loss of the system but is limited to a maximum calibration of 30 dB.

Image of FIG. 6.
FIG. 6.

Measured frequency spectrum with the diagnostic placed in the in-line ECE feedback unit on TEXTOR being partly calibrated. The original 320 000-sample waveform size is reduced to only 5000 frequency bins, limiting the frequency resolution to 0.8 MHz. The peak of the test source at 138.8 GHz, −40 dBm is clearly visible. The dynamical range is .

Image of FIG. 7.
FIG. 7.

Calibrated plot (see Fig. 5) of time-resolved frequency spectra of millimeter-wave radiation in the TEXTOR tokamak, shot No. 108086. The DED is used to move the magnetic island slightly back and fourth through the observation region with a frequency of about 2 Hz. The thin green lines in the 139.8 GHz range are the reflections on the plasma of the gyrotron and one of its harmonics. The gyrotron signals are being suppressed below 120 dB. The frequency resolution is 4 MHz with a time resolution of 1 ms. The dynamic range of signal power exceeds 60 dB.


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Table I.

High-speed data acquisition systems examined.

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Table II.

Trade-off matrix indicates the performance of the various types of digitizers. The cPCI system of Acqiris meets or exceeds all requirements. Digitizer performance is indicated per channel, if applicable.

Generic image for table
Table III.

Calculation of the total equivalent noise temperature of the heterodyne receiver. The total equivalent noise temperature is used to calculate the total NF.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Development and testing of a fast Fourier transform high dynamic-range spectral diagnostics for millimeter wave characterization