Table 4-4. BER Test Control Settings.

TM 11-5820-803-12

Control

Position

ALARM RESET/OFF

OFF

TRANSMIT SOURCE

LINK

TRANSMIT ERROR CODING

Same as normal operational setting for RECEIVE ERROR CODING switch

(table 3-2).

INPUT DATA RATE

Same as normal operational setting of SYMBOL RATE switches if no error

coding is used; one-half the normal operational setting of the SYMBOL

RATE switches if error coding is used.

DIFF ENCODE

Normal operational setting (table 3-2)

DIFF REECHOED

Normal operational setting (table 3-2)

SYMBOL RATE '

Normal operational setting (table 3-2)

RECEIVE ERROR CODING

Normal operational setting (table 3-2)

METER

ERROR COUNT

error rate for each Eb/No, value is plotted on the

modem terminal interfaces (70 MHz input and output)

theoretical bit error rate performance graph (fig. 2-4).

must be disconnected from the terminal to conduct this

Actual performance must be within 1.8 dB of the

test. Weekly testing is recommended; however, the test

appropriate theoretical coding curve. The selected E/N,,

schedule may vary depending on the operational

values for the coding options are:

requirements at the site.

Coding

Eb/No, in dB

(2) To perform this test, a calibrated energy

per bit to noise density (El/N,) ratio must first be

Differential

3, 5, and 11.5

established (para 3-10d). The calibrated noisy signal

Internal

5, 7, and 8.5

required may be generated by using the Test Set,

External

3 and 5.5

Modem TS-3580( )/G. Bit error rate measurements are

then made (b below), using this noisy signal, to verify that

b. Bit Error Rate (BER) Measurement.

the modem is operating within tolerance.

(1) If modem is deenergized, perform the

(3) To provide a more comprehensive

preliminary starting procedure (para 3-4).

indication of the actual bit error rate performance of a

(2) Set the modem controls per table 4-4 and

PSK modem, bit error rate measurements are taken for

connect the equipment per figure 4-1.

several Eb/No, values. The selected E,/N,, con values

are based on the type of coding used. The measured bit

Figure 4-1. Bit error rate measurement, test setup.

4-3