Single-Point Direct Method for Calibration of Io

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  • Signal generator output calibrated in absolute dBm
  • Power meter for checking the signal generator calibration

This calibration method uses the TTY setup commands.

  1. Use the power meter to check the calibration of the signal generator.
  2. Turn off the radiation and connect the signal generator to the test signal injection point.
  3. Raise the antenna to at least 20°, and set the azimuth to point away from any known RF sources including the sun.
  4. Select the pulse width using the Mt command.

    See Mt — Triggers and timing.

  5. Select the pr command and use the commands to set the following: 
    Plotting Received Power Spectrum...
Rx:Pri, Zoom:x1-x8, Navg:25, Start:100.01 usec (14.99 km), Span:50 usec
  6. Set the signal generator to the approximate radar RF frequency with a power level corresponding to a strong signal (30 dB above the noise), and use a CW signal (not a pulse).

    This signal should be visible as a peak in the spectrum display.

    Adjust the signal generator's RF signal frequency so that it produces the precise IF frequency (for example, IF frequency of 30 MHz).

  7. Turn the signal generator off and record the Filtered power level.

    Because of large averaging, it takes several seconds for the average to stabilize.

  8. Turn the signal generator on, verify that the peak is still at the IF frequency and adjust the power level to obtain precisely 3 dB more Filtered power than was observed with the noise only.

    Allow several seconds for the averaging to stabilize after you make each amplitude adjustment.

    This is the value of Io, that is, the test signal power equals the noise power.

  9. Correct the value for losses.

    See Treatment of Losses in Calibration.