For comparison, these cables show the following attenuation characteristics*:

RG-6A/U: Down approximately 3 dB for 100 feet at a frequency of 100 Mc/sec.

RG-114A/U: Down approximately 3 dB for 100 feet at a frequency of 100 Mc/sec.

5.2.4 The Effect of Temperature on Pulse-Height Attenuation and D-C Resistance

A variety of cables were tested for pulse-height attenuation at several temperatures. A description of the cables is given in Table 5-2, and the results of the tests are shown in Figure 5-5.

The main contributor to variation of attenuation with temperature is variation of the resistivity, д of the conductor. A plot of measured resistance of several materials, normalized to 20 mils diameter by 100 feet long, versus temperature is given in Figure 5-6.

Note that the theoretical data do not include calculations for the cables using nickel or nickel clad copper as conductors, because the attenuation equations are not valid for cables having conductors with magnetic properties.

Note, also, that the above procedure is valid only for cables in which the attenuation at f = 1/(2T) is not much greater than that at low frequencies. If these two attenuations are significantly different, the shape of the pulse changes in traveling along the cable and the method of calculating output pulse height would be more involved than the approximate method outlined above. The ratio of high-frequency to low-frequency attenuations is given by

where p is in ohm-meters and a, b, and x are in feet.

♦Catalog W2, American Phenolic Corporation.

TABLE 5-2

CABLE DESCRIPTION

СЛ. —————————- .

1 ‘

~ NOTE: Quartz fiber insulated cables have braided guards and shields of 4-mil wire.

0 TOO 200 300 400 500 600 700 800 TEMPERATURE (°F) ‘

Figure 5-6. D-C Resistance Variation With Temperature — Normalized to 20 Mils Diameter