MIL-STD-469B APPENDIX A
obtained in the open field, the overall coupling from the radar antenna terminals to the test antenna terminals
is required for application in the data reduction. The coupling factors and attenuation values are required over the entire frequency range covered by the emission spectrum measurements.
40.4.4 Procedure. The block diagram for the transmitter emission test is shown on figure 10. This test should normally be performed as a closed system test in accordance with the test point selection priority list (see 30.16.1).
40.4.4.1 The test procedure for closed system measurements applies to open-field measurements except that the point of measurement is the test antenna terminals rather than signal sampler output. Therefore, the antenna-to-antenna coupler factor replaces the signal sampler coupling factor in the data reduction process. In either case, the radar signal level at the sample point is termed P 2.
40.4.4.2 If open-field measurements are necessary, the test antenna should be located as described (see
50.2). With the radar antenna scan stopped, the alignment of the radar and test antenna should be adjusted for maximum signal at the test antenna terminals. The test antenna polarization should be the same as that of the radar antenna.
40.4.4.3 With the sample point connected to the spectrum analyzer through the appropriate transmission line and calibrated attenuators, the analyzer should be tuned until the radar signal spectrum appears centered on the analyzer display. This adjustment is performed using the maximum analyzer bandwidth. The final analyzer bandwidth should be selected using the following procedure:
a. Adjust external attenuators for an on-scale display.
b. Decrease the analyzer bandwidth in increments (a 1:3:10 sequence is normally available) and photograph the resulting displays.
c. Determine the maximum analyzer bandwidth for which the shape of the spectrum display (envelope) is independent of the bandwidth setting (i.e., no longer changes as bandwidth is reduced).
d. The analyzer bandwidth determined in step c. should be used for obtaining emission spectrum
data (photographs) at the radar F o and required points in the spectrum away from F o (e.g. B 40dB).
The analyzer IF bandwidth (3 dB) determined in step c. should satisfy the relationship B
NOM>1.7 PRF for
pulse radars. The analyzer controls and external attenuators should be adjusted to provide the maximum
amplitude on-scale display that does not result in overloading the analyzer input. The analyzer should be checked for signal overload as follows. After the analyzer controls and external attenuators are set, a 10 dB external attenuator should be added at the analyzer input. The amplitude of the spectrum envelope should decrease by a corresponding 10dB over all parts of the display. If a 10dB decrease is not noted, the analyzer controls and external attenuators should be changed as required to produce the desired 10 dB decrease when the overload check is performed. After verifying that overload is not occurring, the 10 dB attenuator added for the check should be removed.
40.4.4.4 The analyzer sweep width should be adjusted for an optimum display showing the first null points on each side of the maximum emission at F o. The sweep time should be selected to satisfy the following inequality:
(B )2(T IF )>5
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