(b)
Then attach a short length of cable (with impedance the same as the adapter, i.e., 75 ohms) to the adapter.
(c)
Attach the test cable to the CABLE connector.
S 862-021
(20)
With the mp/DIV control set at 500, move the trace on the display so that the cable shows on the display.
S 862-022
(21)
Adjust the GAIN control until the open end display (reflected pulse) is set two divisions above the cable display (horizontal center line). (This sets the reflected pulse to +1p from the characteristic impedance.)
NOTE: If an impedance adapter is not used, secondary reflections
____ will show as discontinuities after the open end of the cable.
S 862-023
CAUTION: DO NOT ATTACH LIVE CIRCUIT CABLES TO THE INPUT OF THE TDR.
_______ VOLTAGES MORE THAN 5 VOLTS CAN CAUSE DAMAGE TO THE SAMPLING GATE OR TUNNEL DIODE.
(22) Bleed the cables before you attach them to the test set to remove static charge from them. The 50 ohms termination and BNC adapter supplied can be used to bleed a cable charge.
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S 862-024
CAUTION: DURING AN ANTENNA TEST, DO NOT OPERATE CLOSE TO TRANSMITTERS
_______ THAT CAN OPERATE AT THE FREQUENCY THE ANTENNAS RECEIVE. THIS CAN CAUSE DAMAGE TO THE TDR.
(23)
Remove the precision 50-ohm cable from the CABLE connector. Put it in its container.
S 862-025
(24)
Attach the TDR adapter cable to the BNC connector on the front panel of the TDR.
S 862-026
CAUTION:_______DO NOT DIRECTLY TOUCH THE RACK CONNECTORS. THIS CAN CAUSE DAMAGE. USE A BREAKOUT BOX.
(25)
Attach a breakout box to the rack connector (Table I).
S 862-027
(26)
Attach the adapter cable connector to the applicable test point on the breakout box (Table I).
D. Coaxial Cable Fault Location Test
S 862-028
(1)
Turn the DISTANCE switch clockwise until the reflected pulse is on the reference display line. (The value on the DISTANCE switch times the multiplier gives the length from the CABLE connector to the end of the cable or to the failure).
S 762-029
(2)
Measure the Voltage Standing Wave Ratio (VSWR) of the test cable.
NOTE: A 20 percent difference of pulse from a 50 ohm reference line
____ is equal to a VSWR of 1.5:1. A 33 percent difference is equal to a VSWR of 2.0:1. If the VSWR is 1.5:1 or less, the system is good.
(a) Keep a record of the value (Include comments and steps done).
S 762-030
(3) Measure the fault location of the test cable.
(a) Keep a record of the location (include comments and steps done).
NOTE: All cable lengths of antenna systems are very important.
____ It is recommended that you replace defective cables and not repair them.
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MAINTENANCE MANUAL
~.............................................................................. | Cable Test Result Chart | | Table I | ................................................................................ | | | | | |MEASURED | | | | | | | |VSWR (20% | | | | | |RACK | |DEV=1.5:1)| | | | |CABLE |CONNECTION |BREAKOUT |(33% | | | |CABLE TYPE |LENGTH |POINT(S) - |BOX TEST |DEV=2.0:1)| | | SYSTEM |IMPEDANCE |FT/IN |CONNECTOR |POINT(S) - |AND ACTION| | | (REFERENCE) |IN OHMS) |*[2] |(PIN) |BLOCK (PIN)|TAKEN | VP | ................................................................................ |ADF-L *[1] |24 Gauge |55/0 |*[1] |*[1] | |NA | |(WDM 34-57-11)| (75) | | | | | | ................................................................................ |ADF-R *[1] |24 Gauge |52/0 |*[1] |*[1] | |NA | |(WDM 34-57-21)| (75) | | | | | | ................................................................................ |ATC-L (T) |*[4] RG393/U|25/10 |B(71) |C(12) | |0.69 | |(WDM 34-53-11)| (50) | | | | | | ................................................................................ |ATC-L(B) |*[4]RG393/U |25/11 |B(71) |C(12) | |0.69 | |(WDM 34-53-11)| (50) | | | | | | ................................................................................ |ATC-L *[5] |RG393 |11/0 |B(71) |C(12) | |0.69 | |(WDM 34-53-11)| (50) | | | | | | ................................................................................ |ATC-R(B) |*[4]RG393/U |26/2 |B(71) |C(12) | |0.69 | |(WDM 34-53-11)| (50) | | | | | | ................................................................................ |ATC-R(T) |*[4]RG393/U |26/0 |B(71) |C(12) | |0.69 | |(WDM 34-53-11)| (50) | | | | | | ................................................................................ |ATC-R *[5] |RG393 |17/0 |B(71) |C(12) | |0.69 | |(WDM 34-53-21)| (50) | | | | | | ................................................................................ |DME-L |RG393/U |24/0 |B(71) |C(12) | |0.69 | |(WDM 34-55-11)| (50) | | | | | | ................................................................................ |DME-R |RG393/U |23/0 |B(71) |C(12) | |0.69 | |(WDM 34-55-21)| (50) | | | | | | ................................................................................ |HF COM-L |5021K1011 |145/0 | B(71) | C(12) | | 0.80 | |(WDM 23-11-11)| (50) | | | | | | ................................................................................ |HF COM-R |5021K1011 |143/10 | B(71) | C(12) | | 0.80 | |(WDM 23-11-21)| (50) | | | | | | ................................................................................ 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：757 AMM 飞机维护手册 STANDARD PRACTICES - AIRFRAME(81)
