MIL-STD-469B APPENDIX A
60.4.4.1 The tunability test should begin by tuning the radar receiver for normal operation on one of the test frequencies specified. The test signal should be modulated to equal the nominal characteristics for which the radar system or equipment specifications are given. The test signal should be triggered from the radar modulation trigger, with a delay to place the signal at an equivalent range such that any sensitivity time control (STC) is not activated (unless allowance for the effect of STC has been made in establishing the standard response). The test signal should be tuned to the receiver frequency. The receiver output should be monitored with the oscilloscope. The generator level should be adjusted to obtain the standard response at the receiver output. The generator frequency should be measured with the frequency counter and the value recorded along with the receiver output level required for the receiver output standard response. The procedure should be repeated for the remaining receiver test frequencies as specified. The entire procedure should be performed with the radar system or equipment operating under the environmental temperature conditions as specified.
60.4.4.2 The receiver frequency stability should be determined by accurately measuring the frequency stability of the local oscillator frequency with the frequency counter. In case of the multiple conversion receiver, the frequency of all local oscillators should be measured. The time over which the receiver stability is measured should include the stability requirements specified by the contracting activity or contract. The frequency stability test should also include the frequency measurement over a period of 4 hours at the following intervals:
a. Within first hour: After receiver turn-on, at time T o, measure frequency at 10-second intervals during first 2 minutes of operation. Beginning at times of T o + n minutes, where n = 5, 10, 15... up to 60, measure frequency at 10-second intervals for a period of 1 minute.
b. Over the next 3 hours: Measure frequency at time of T o + 60 + n minutes where n = 0, 10, 20,
30... up to and including n = 180.
The turn-on time in a. from a cold start may vary from one piece of equipment to another. Turn-on time will be defined as "the earliest time, from a cold start, that the equipment is intended to radiate and receive signals". The receiver tuned frequencies at each point over the required time interval should be determined from the measured local oscillator frequency and the receiver intermediate frequency. The variation in the receiver tuned frequency at times T o + n compared to the tuned frequency at time T o should not exceed the frequency tolerance as specified.
60.4.4.3 Sample data forms for recording receiver tunability and frequency stability measurements results are shown on figures 34, 35, and 36.
60.4.5 Sample calculations. The results from the receiver tunability measurements typically consist of the receiver sensitivity measured at the required test frequency (see 60.4.2). Sample calculations for spurious response (see 60.3.5) are applicable for sensitivity measurements. The results from the receiver frequency stability test consist of receiver local oscillator(s) frequency measurements and associated information such as mode of receiver operation, cold start time, turn-on time, and time for each frequency measurement point.
60.4.5.1 In the stability data reduction, the measured local oscillator frequency is first converted to the equivalent frequency at the receiver input.
Measured data:
Local oscillator frequency at start of test (F , T ): 1250.764 MHz
Local oscillator frequency at time T 1 (Flo, T1): 1250.748 MHz
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