6.3 TDR Test

A TDR test is used for troubleshooting the transmission line when performance problems occur. It is not a requirement for verification of performance, but a measurement, after installation, is useful as a record when problems may occur.

EQUIPMENT: HP-8753A Network Analyzer and an HP-85046A S-Parameter Test Set (or equivalent).

TEST:

(1) Calibrate the equipment.

(2) Using the VSWR test adaptors, attach a 50-ohm load at the antenna end of the line and interface the transmitter end to the test equipment.

(3) Examine the TDR trace for variations in transmission line impedance.

NOTES:

When using the HP equipment as a TDR, use an upper frequency of 30 MHz to allow long lengths to be tested. At 30 MHz:

  • Section bends will appear as (negative) impedance variations, normally no larger than 0.25 ohm.

  • Other than bends, impedance variations are no larger than 0.10 ohm. However, due to dimensional tolerances, variations in impedance over longer distances may be ±0.25 ohm.

    For fault detection, the locations where the cable should be examined are determined when results such as the following are observed (at an upper frequency limit of 30 MHz).

  • At locations where the impedance variation exceeds 0.50 ohm.

  • At locations where the impedance variation in a straight cable section exceeds 0.25 ohm.

  • At locations where the impedance variations differ by more than 0.25 ohm from initial data recorded after installation (if available).

    7. PERFORMANCE CHARACTERISTICS

    7.1 General

    Nominal size: 10 inches (254 mm)

    Impedance: 50 ohms

    Cable type number: SCL950

    7.2 Electrical Characteristics

    Maximum frequency: 510 MHz
    		• Velocity: 97.5%

    Unpressurized cable peak power rating:

    DC-based: 5760 kW

    RF-based: 2820 kW

    Average power rating for specific conditions of VSWR, temperature, and and pressure:

    Condition Condition Condition
    Frequency A B C
    1 MHz 2820 kW 7560 kW 7900 kW
    10 MHz 2110 kW 2390 kW 2500 kW
    26.1 MHz 1310 kW 1480 kW 1550 kW



    Parameter    		 Condition
    A    		 Condition
    B    		 Condition
    C
    VSWR 1.0 1.0 1.0
    Ambient
    temperature    		 104°F
    (40°C)    		 122°F
    (50°C)    		 122°F
    (50°C)
    Inner
    conductor
    temperature    		 302°F
    (150°C)    		 302°F
    (150°C)    		 302°F
    (150°C)
    Pressure 1 bar 2.5 bar 3 bar


    Attenuation at:

    1 MHz: 0.005 dB/100 ft (0.14 dB/km)

    10 MHz: 0.014 dB/100 ft (0.46 dB/km)

    26.1 MHz: 0.023 dB/100 ft (0.76 dB/km)

    VSWR in HF broadcast bands: 1.05

    7.3 Mechanical Characteristics

    Outer conductor: Aluminum

    Inner conductor: Copper

    Diameter over outer conductor: 10.0" (254.0 mm)

    Weight including flanges: 5.2 lb/ft (7.7 kg/m)

    Maximum overall shipping length: 38.9 ft (11.86 m)

    Recommended minimum bending radius: 20 ft (6.1 m)

    Standard section length: 38.0 ft (11.58 m)
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