TM 11-5840-360-14-1-1
NOTE: The loss of six feet of RG
6. Measure pulse width (PW) and pulse repetition
214/U coaxial cable is approximately
time (PRT) from oscilloscope display; record both in
terms of seconds (PW = 1 x 10-6 sec, PRT = 1.11 x 10-
1.1 dB at S-band frequencies. The
3 sec).
actual loss of the test cable should
be measured at 3050 MHz.
7. Calculate radar duty cycle (0.0009) as follows:
7. Connect oscilloscope at receiver output
PW
connector A9J1 in Receiver Transmitter RT-1241;
Duty Cycle = PRT
trigger oscilloscope from pulse generator.
8. Adjust signal generator attenuation and
8. Calculate transmitter peak power (50 kW
frequency controls to identify test video signal on
minimum) as follows:
oscilloscope; set attenuation control for non-saturating
test signals and carefully adjust frequency vernier to
Average Power Recorded in Step 4
maximize test signal amplitude.
Peak Power = Duty Cycle Calculated in Step 7
9. Increase signal generator output attenuation
setting until test signal is just visually discernible in the
5.24.2 Receiver Sensitivity (Minimum Discernible Signal
displayed noise.
- MDS) Measurement
NOTE: Adjustment of the pulse
1. Set (master) Indicator POWER switch to ST BY.
generator delay control will aid in
2. Calibrate signal generator (HP 8616A or
identifying the test signal at the
equivalent) output power level at 3050 MHz per its
threshold of discernibility.
instruction manual.
3. Set signal generator controls as follows:
10. Verify MDS, calculated as follows, is less that or
equal to -98 dBm.
MDS = (Signal Generator
a. Frequency: 3050 MHz
Attenuation) - (Directional Coupler Attenuation) (Test
b. Output Level: -67 dBm
Cable Attenuation)
c. Modulation: External pulse
NOTE: For 20 dB directional coupler
4. Adjust pulse generator (or equivalent) for an
loss and 1.1 dB cable loss, the signal
output pulse having the following characteristics:
generator must be set to -76.9 dBm
or less for an MDS of -98 dBm.
a.
Voltage: 25 5V peak
5.24.3 Antenna/RF Cable VSWR Measurement
b.
Frequency: 1800 Hz
c.
Width: 10 usec
1. Perform steps 1 through 11 of paragraph 5.23.3.
d.
Rise/Fall Time: 2 usec maximum
2. Convert return loss to VSWR using the chart
given in paragraph 5.23.3; verify VSWR is less than
5. Connect pulse generator output at signal
1.67.
generator external pulse modulation input.
6. Connect signal generator RF output to
NOTE: The VSWR requirement is
FORWARD port of directional coupler using six foot
1.65:1; this requirement is based on
RG214/U coaxial cable.
a 1.5:1 VSWR for the rotary joint and
antenna and a 1.1:1 VSWR for the RF
interconnecting cable.
5-121
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