Radar Field Analyser - RFA641 Edition Date: 28-Feb-18
6. A measurement can always be interrupted by clicking the Stop button.
7. When all channels are measured, click the Save button to save the measurement data to disk.
The VI will prompt a standard file dialog, by default pointing to the CALIB subdirectory of the MSSR
or PSR subdirectory of the active campaign folder. Type in the desired file name and save the data
to disk or select Cancel if you do not wish to save the results.
4.2.4. Troubleshooting
1. A “File not found” message pops up the minute you run the instrument
◦ Check whether the RFA calibration files are installed correctly.
4.3. STC/DSTC Calibration
4.3.1. Theory
The STC measurement result consists of an RF input power versus time table. To be able to measure the
gain vs. time delay, the RFA641 needs to be synchronised to the interrogation signal of the radar under test.
The position of the RFA641 transmitters output pulse is then altered in discrete steps, ranging from a set
maximum (Stop Delay) to a minimum (Start Delay). The power level for the measurement pulses can be set
in the Tx power control. Make sure that the power of the measurement pulses is within the receiver range.
Two measurement methods are implemented:
1. STC: Measurement of the STC curve in case the STC is implemented in the receiver and directly
measurable at the output of the receiver. The RFA641 will inject pulses of a fixed (selectable) power
level into the receiver. These pulses will then be varied in time delay vs. the interrogation trigger. The
(M)SSR’s analog video output signal is then sampled by the RFA641. This amplitude is passed
through the calibration curve in order to build the STC curve: a gain [dB] versus time delay curve.
2. DSTC: In this case the STC is implemented after the receiver section, by applying a variable
threshold when digitising the video. Therefore the video level to be sampled for each of the receivers
is the quantised video. The Radar Field Analyser will inject pulses starting from a minimum delay up
to a maximum delay. For each delay step the power level injected starts from the selected maximum
power level and is decreased down to the DSTC trigger level. Depending on the delay, from a certain
RF power level, the pulse will not pass the digitising threshold anymore and disappears at the
quantised video output. By presenting the measured threshold level vs. time delay, the Digital STC
curve becomes visible.
4.3.2. Getting Started
The STC/DSTC Calibration is loaded from the RASS-S Toolbox using the Rx button.
In case of an STC measurement make the connections as shown in Annex 3: Rx, Bandwidth and STC
Calibration Connection Diagram, in case of a DSTC measurement make the connections as shown in Annex
4: DSTC Calibration Connection Diagram.
IE-UM-00165-005 RFA641 User Manual.odt 49/110
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