Manually calibrating signal processor

note For manual siggen control, it is best if the control for the signal generator and the workstation are located next to each other. Otherwise, 2 people and some coordination are required to perform a calibration.
cautionCaution The sensitivity and dynamic range of the radar can be affected by the gain of the IF signal entering the IFD. First adjust the IF signal level (see the test procedure in RVP10 User Guide (M212604EN)).

To protect the signal generator, the radar is not usually set to transmit during calibration. Check with your manufacturer. If it is OK to transmit while the siggen is connected, it better simulates operating conditions. If transmitting is not recommended, turn everything on, but do not set the transmitter. This assures that all sources of noise are accounted for.

  1. Set the antenna elevation greater than 20° to reduce the effect of earth temperature noise which is detectable by modern, sensitive receivers.

    If you are transmitting, this eliminates the possibility of weather signals interfering with the calibration.

  2. Check that the signal generator is set for the CW (continuous wave) operation and not for pulse mode operation.
  3. Select a pulse width.

    Note that the pulse width lines of the DSP issue the appropriate signal. If this control is implemented on your system through the antenna controller, it is set correctly.

  4. Set the plot range limits.

    If you do not know what limits to set, use the system defaults. You can adjust them later without losing data.

  5. Collect the plot points for the calibration:
    1. Enter the siggen value in the unlabeled field next to Sample. You can use the slide bar.
    2. If the siggen is not controlled by the RCI, set the signal generator output to match the specified value. Otherwise, this is done for you.
    3. Select Sample.

      Zauto draws the point on the calibration plot

    Repeat these steps until you have collected a sufficient number of points (for example, 6 points in the linear range of the curve). If you make a mistake, select Delete to remove the point or reset the pulse width and start again.

  6. After you have collected the points, set the plot limits to include only those points in the linear range.
  7. Turn down or disconnect the signal generator and select Noise.

    A horizontal line is drawn at the average noise level.

  8. Select Fit.

    Check the line and results to make sure they are reasonable.

    Reset the limits or collect more data as required to get a representative fit to the straight line portion of the curve (typically from 15 dB above noise to 70 dB above noise).

    The calibration results are filled in each time you select Fit.

  9. When you are satisfied with the calibration, select Update to update the View Calibration display.

    You can use results from one pulse width to update other pulse widths. However, for the most accurate results, you should perform a separate calibration for each pulse width.

    Errors are likely to be less than 3 dB if the update technique is used.

  10. Move on to the next pulse width, if necessary, starting with 3.
  11. When you are finished, check that the View Calibration display shows the values that you want to save.
  12. Select File > Save and then File > Exit.
tip

You can also modify the calibration file, using the Zcal utility to enter the calibration reflectivity by hand.

You typically use the Zcal for testing or after a component has been replaced by another with known calibration.