Cable classification

TM 11-5820-803-12

in the installation. Cable selection may be simplified by

(but only one) of the following outputs may be connected.

using the length requirement to determine the maximum

(1) 75-ohm balanced cable driver.

value of the loss characteristic (a) at 5 MHz which can be

(2) 75-ohm unbalanced cable driver.

used. The maximum value of a can be determined from

(3) 50-ohm unbalanced cable driver.

the relationship:

(4) LOS microwave driver.

Èmax = 3000 ÷

2-10. Test and Monitor Capabilities.

(2) Cable classification. The transmission of

a. Link Test. The PSK modem provides the

baseband data over an interconnect facility cable results

capability, with adequate coordination between earth

in unequal phase distortion at the output. The PSK

terminal sites, of measuring the quality of a digital

modem LOS/cable receiver and decoder circuits contain

communications link. The transmit link test setup (para

equalization networks to compensate for this phase

3-6) provides instructions for using the PSK modem to

distortion.

Detailed instructions for adjusting the

transmit an internally generated 2047 bit sequence over

equalizers are given in paragraph 2-21.

Further

the satellite link. The receive link test procedure (para 3-

information on configuring the LOS/cable receiver and

7) provides instructions for using the PSK modem to

decoder circuits to provide the appropriate equalization is

receive this same sequence from a satellite link, perform

given in paragraph 2-20, depending on whether the cable

an internal data comparison, and determine the error

is classified as long, medium, or short. Although the

rate introduced in the link. If necessary, the test may be

phase distortion is not directly related to the 5 MHz cable

performed for communications transmitted from a site

loss, the parameters are so closely related that cable

without disturbing the communications being received,

loss may be used to determine the equalization

and vice versa.

requirements.

To determine cable classification,

b. Terminal Test. If an earth terminal is configured

calculate the cable loss based on the cable length and

to receive its own transmissions, the link test capabilities

attenuation factor at 5 MHz (loss = È5/100) and assign

of the PSK modem may be used to determine the

the appropriate classification in accordance with the

operational status at the terminal.

following list to ensure proper alinement (para 2-21).

c. Self-Test. The PSK modem contains internal

self-test circuits which play a major role in the fault

Cable loss at 5 MHz

Classification

isolation of the modem.

In addition, this self-test

0 dB to 3 dB

short

capability provides a means of rapidly verifying modem

3 dB to 12 dB

midrange

operation to aid in isolating a communication system

12 dB to 30 dB

long

malfunction.

d. Signal-to-Noise Indication. The PSK modem

c. Input Signals. The desired input from the ICF

contains a circuit which monitors the operation of the

modem is internally selected at installation. Details for

baseband conditioner in the receiver during normal

the LOS/cable receiver and decoder input selection are

communications.

The resulting front-panel meter

given in paragraph 2-20f. The modem must also be

indication may be used to estimate the input signal-to-

configured to derive internal timing from and transmit the

noise ratio to the PSK modem (fig. 2-15) or the error rate

selected ICF input. Any one of the following input

occurring in the received data (fig. 2-16). For the most

sources may be selected:

accurate results, the operator should be instructed to plot

(1) 75-ohm balanced cable.

calibration curves at the operational data rate of the

(2) 75-ohm unbalanced cable.

receive link. The data for calibration curves is collected

(3) 50-ohm balanced cable.

by performing the noise test (para 4-6) and noting the

(4) LOS microwave receiver.

error rate and meter reading for each value of (Eb/No)

tested.

NOTE

e. On-Line Fault Monitoring. The on-line fault

If a cable is used for the ICF interface,

indicators monitor various characteristics of the signals

the required equalization procedure

being processed by the system. It is recommended that

is given in paragraph 2-21.

the function of the indicators be reviewed and utilized in

d. Output Signals. All outputs available to the ICF

the site operating and troubleshooting procedures.

system are present at the PSK modem rear panel and

their levels are controlled by a single internal switch.

Detailed instructions for setting this switch are given in

paragraph 2-20e. Any one

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