MIL-STD-469B APPENDIX A
60. RADAR RECEIVER MEASUREMENTS
60.1 Requirements summary. The radar receiver measurements and procedures described in this section provide data for comparison to the acceptance bandwidth, susceptibility characteristics, frequency tolerance, tunability and oscillator radiation requirements and limits (see 5.5).
60.2 Overall selectivity.
60.2.1 Objective. The objective of this test is to determine the receiver response characteristics at and near the receiver tuned and image frequencies.
60.2.2 Requirements. The overall receiver selectivity characteristics should satisfy the requirements
(see 5.5) for the appropriate category of radar.
60.2.3 Application notes. In the first part of the test, the receiver response to test signals at and near the radar tuned frequency should be determined. In the second part, the response to test signals at and near the receiver image frequency should be determined. Both parts should be performed with the radar receiver tuned to the mid-frequency of its tuning range (F M). If the receiver switches bandwidth during its operation, this test should be repeated for each bandwidth used in the radar operation.
60.2.3.1 The receiver selectivity characteristics give an indication of the overall gain and sensitivity of the receiver at its tuned frequency as well as its responses at frequencies slightly removed from the tuned frequency. The selectivity characteristics are mostly determined by the IF amplifier tuned circuits and should be fairly symmetrical about the center frequency. The level of these responses near the fundamental and image frequency indicate the ability of the receiver to discriminate against off-channel radiation through the acceptance bandwidth or selectivity.
60.2.3.2 The radar receiver measurements specified herein should be performed on all receivers of the same radar except in the case of phased array radars with more than fifteen identical parallel receivers. For these radars fifteen of the receivers should be selected through the use of a table of random numbers. The standard deviation of the measured data, corrected for any antenna weighing, should be calculated. If the standard deviation is greater than 2.0 dB, additional receivers should be measured. The number of receivers to be measured should be determined using the student-t distribution. The total receiver response (all receivers) should then be determined statistically.
60.2.3.3 For pulsed radar receivers, the test signal generator should be modulated with a pulsed signal which is approximately 10 times the longest operating pulsewidth for the tuned circuit being measured. The wide pulsewidth produces a relatively narrow energy spectrum in comparison to the receiver bandwidth. This narrow spectrum avoids erroneous bias buildup in the receiver's gain control circuits. In addition, the narrow spectrum provides a close approximation of the CW selectivity characteristics of the receiver.
60.2.3.4 For nonpulsed receivers, the test signal should be unmodulated (CW). The point for measuring the receiver output should be past the receiver second detector, if possible, and should give a signal which represents normal operation of the system.
60.2.4 Procedure. The block diagram of the test setup should be as shown on figures 25 and 26.
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