Radar Field Analyser - RFA641 Edition Date: 28-Feb-18
4.4.3. Software
The program will ask to load the correct receiver calibration file. The receiver calibration file is required in
order to be able to calculate the exact power level corresponding to the measured pulse amplitudes. The
Down Calibration table2.vi will pop up with a dialog box to select a calibration file. Select the file and click
OK. The selected calibration file is then displayed. By clicking Cancel in the file dialog it is possible to select
a default table, in case no receiver calibration file is available. Use Slope and Offset to change the default
table to your needs. The calibration file can always be reloaded afterwards using the Load Rx Calibration
button.
1. Adjust the Power settings as required. Select the correct Tx frequency (default 1090MHz) and the
correct Attenuation value. The Power control sets the power level present after the extra
attenuation at the RFA641’s Tx connector, so indicating the power injected in the radars receiver
input. The max. output power of the RFA641 is guaranteed +10dBm at 1090Mhz. Choose a level in
the linear calibration part of the radar receiver to obtain a satisfactory result. Typically it is set so that
the receiver receives a power level of -40 to -50 dBm.
The external attenuator added is typically 30dB in order to reach the maximum receiver input power
of about -20dBm. In most cases however, the connection will take place through a fixed coupler
already present in the system. This attenuation must also be taken into account when filling in the
Attenuation parameter. Therefore if the receiver is measured through an extra fixed coupler of
30dB, the transmission power must be set to -50dBm, extra attenuation in this case is 60dB.
The program will synchronize to the ARP and interrogations of the radar. The azimuth information is
indicated in the PPI Pict window. Once the number of interrogations per revolution (IPR) is constant,
the azimuth can be calculated correctly and the measurement buttons are enabled.
2. Set the time sweep parameters: The sweep Start Delay is used to determine the time delay
between the first test pulse and the trigger pulse. The Stop Delay is used to determine the time
delay between the last test pulse and the trigger pulse. The RFA641 transmits a set of 128 RF
pulses, spread over the selected range from the set minimum (Start Delay) to the set maximum
(Stop Delay) to measure the complete STC at once at the azimuth of the interrogation.
3. The #sectors parameter determines the number of measurements to be executed during one
revolution. In fact it acts as a divider for the IPR count, so that each IPR/#sectors amount of triggers
a measurement is performed. Each time one of the measurement parameters is changed, the
measurement buttons Sum, Delta and Omega will be disabled until the next ARP occurs.
4. If you want to perform the RFA Selftest/Calibration, this is possible by clicking the Cal RFA
button.
5. Before starting the measurement it is important to check the position of the output pulse and the
setting of the sampling point. Click the Preview button to open the Preview STC.vi window.
IE-UM-00165-005 RFA641 User Manual.odt 53/110
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