C. Prepare to Do a Coaxial Cable Test
S 022-002
(1)
Remove the applicable receiver or transmitter from the equipment rack.
S 862-003
(2)
Set the TDR front panel controls as follows:
~.............................
|FOCUS |Midrange |
...............................
|INTENSITY |Midrange |
...............................
|ZERO REF |Fully cw |
...............................
|POSITION |Midrange |
...............................
|mp/DIV |500 |
...............................
|DISTANCE |000 |
...............................
|FEET/DIV |1 |
| (METRES/DIV) |(.25) |
...............................
|X1-X.1 |X1 |
...............................
|CABLE DIELECTRIC |SOLID POLY |
...............................
|POWER |ON |
2.................…...........1
S 862-004
(3)
Adjust the INTENSITY and FOCUS controls to get a bright trace.
S 862-005
(4)
Adjust the POSITION controls to set the trace two divisions below the horizontal center line.
S 482-006
(5)
Attach the precision 50-ohms cable in the container to the CABLE connector.
S 862-007
(6)
Turn the ZERO REF SET control through its range to make sure that you can set the incident pulse edge on all vertical lines. (The incident pulse edge is the initial rise of the step pulse.)
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MAINTENANCE MANUAL
(7) S 862-008Turn the ZERO REF SET switch counterclockwise until the incident pulse edge is on a vertical reference line. (The vertical reference line can be one of the lines from the center line to the left side of the CRT display.)
(8) S 752-009Set the DISTANCE switch to 050. (a) Make sure that the top of the step (open cable reflection) shows.
(9) S 752-010Push the ZERO REF CHECK switch. (a) Make sure that the incident pulse edge goes back to the vertical reference line.
S 862-011
(10)
Set the DISTANCE switch to 000.
S 862-012
(11)
Change the mp/DIV to 50.
S 862-013
(12)
Adjust the POSITION controls until the top of the incident pulse is on the horizontal center line.
S 752-014
(13)
Push the NOISE FILTER switch.
(a)
Make sure the noise on the display decreases.
(b)
Make sure the scan rate decreases.
S 862-015
(14)
Set the mp/DIV to 500.
S 862-016
(15)
Push the NOISE FILTER switch.
S 862-017
(16)
Lift and hold the RECORD switch in the up position.
(a) Make sure that a bright mark shows at the left edge of the CRT.
S 862-018
(17) Release the RECORD switch. (The slow scan of the mark traces the waveform. When the scan is done, the TDR will automatically go back to its usual scan mode.)
NOTE: All of the antenna cables other than the ADF are 50 ohms.
____ The ADF is 75 ohms.
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MAINTENANCE MANUAL
S 722-019
(18) For cables with an impedance other than 50 ohms, do the test as follows:
(a) Set the GAIN control (screwdriver adjust) to correct the reflected pulse for +1p at the open end of a cable. (When the GAIN changes, the incident pulse will not be 1 p.)
S 862-020
(19) To set the GAIN for an impedance of other than 50 ohms, use one of the procedures that follows:
(a)
Attach an impedance-matching adapter (50 to 75 ohms) to the CABLE connector.
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