MIL-STD-469B APPENDIX A
figure 13. Note the increase (k, in dB) of the spectrum envelope produced by increasing the analyzer IF bandwidth for identical frequency sectors. In the example as shown on figure 13, k equals 19.5 dB. Photograph the display and calibrate the analyzer frequency and amplitude scales using the procedure given (see 40.4.4.5).
40.5.4.2 When it is necessary to employ the second part of the spurious emission test procedure (where the FSVM replaces the spectrum analyzer), the process for obtaining the k factor should be modified slightly. Using the radar emission bandwidth photograph which shows the rolloff spectrum region for reference, a frequency toward the end of the rolloff where the display amplitude is 10 to 15 dB above the noise should be selected. The FSVM should be tuned about this frequency for a maximum response, and the amplitude for reference noted. A calibrated pulsed RF signal should be substituted at the input to the FSVM. The PRF of the pulsed RF signal should be set to equal the radar PRF. The RF pulsewidth (t) should be adjusted to satisfy the following:
t > 2/BFSVM
where BFSVM is the nominal instrument bandwidth. The frequ
ency of the pulsed RF signal should be adjusted
for maximum response on the FSVM, then the signal level adjusted to obtain the reference FSVM response.
The frequency of the pulsed RF signal should be measured and the value along with the signal level noted. The CW signal level corresponding to the amplitude of the spectrum envelope should be determined in the photograph at the frequency noted. The k factor, in dB, should be determined by comparing the CW signal level (from the photograph), P CW, to the pulsed RF signal level, P PULSE, as follows:
P
k = PPULSE CW
where:
PPULSE an
d P n dBm.
CW are i
40.5.4.3 When spurious emissions, which are 20 dB or more above the test receiver noise level, are found the spectrum analyzer test receiver should be used to determine the power spectral level. The analyzer bandwidth should be returned to the original value used in the radar emission bandwidth test.
40.5.4.4 After the upper frequency limit has been reached (see table VI), the analyzer should be tuned to the frequency corresponding to the lower frequency of the maximum allowable emission bandwidth and the scan for spurious emission should begin below the operating frequency. The entire scan should be performed for each of the three standard test frequencies and at the maximum duty cycle. The same tests should be performed at the mid-standard test frequency using the mean pulsewidth and repetition rate of the system.
40.5.4.5 Spurious emissions measurement test procedures in the open field should be the same as those for the closed system tests except that additional measurements should be made to determine the antenna coupling factor (ACF) from the terminals of the radar antenna to the terminals of the test antenna in the open field over the test frequency range. When the ACF coupling factor is known, it should not be essential for the radar-to-test antenna distance to satisfy the minimum distance requirement given for the radar antenna pattern test. The polarization, bearing, and elevation of the radar and test antennas should be adjusted for maximum signal transfer over each portion of the test frequency range.
40.5.4.6 For the antenna coupling measurement at each frequency, a calibrated CW signal should be applied to the radar antenna input. The level received at the test antenna terminals should be measured with the spectrum analyzer or FSVM. Signal substitution with a calibrated CW signal generator should be used for
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