Nonsecure voice transmission requires circuit parameter VI.
The loss
concerning frequency characteristic of code VI should not exceed the limits
of 8 dB less loss (-) at 0.4 kHz or 20 dB more loss (+) at 2.8 kHz than the
loss at 1,004 Hz.
Loss has to be calculated from levels.
Less loss is
equivalent to a higher level, so 8 dB less loss at 0.4 kHz is equivalent to
a level 8 dB above +2 dBm at 1,004 Hz, or +10 DBm. Conversely, more loss is
equivalent to a lower level, so 20 dB more loss at 2.8 kHz is equivalent to
a level 20 dB below +2 dBm at 1,000 Hz, or -18 dBm.
18. b--Learning event 5, paragraph (d),
page
38
and
DCAC
300-175-9
Extract, table 2, page 80. (appendix).
The maximum net loss is the total loss between the output level of the
sending terminal at 1.0 kHz as compared with the output level of the receive
line amplifier. Table 2 gives the maximum net loss variation parameter for
code VI as 4 dB. Since the output level of the receive line amplifier is
+2 -dBm, the sending level must lie between the limits of dB from that
level, or +6 dBm to -2 dBm, calculated as follows:
(+2 dBm) +(4 dB) = +6 dBm
(+2 dBm) -(4 dB) = 2 dBm
19. d--Learning event 5,
paragraph
(d),
page
38
and
DCAC
300-175-9
Extract, table 2, page 80.
Table 2, item h shows a maximum allowable channel noise to be 43 dBrnc0.
This is 43 dB above the reference level of -90 dBm (O dBrn with C-message
weighting). In terms of actual value of dBm, the noise level will be 43 dB
above the level of -90 dBm, calculated as follows: -90 dBm +43 dB = -47 dBm.
Note that although -47 dBm is a smaller figure than -90 dBm, it represents a
higher level because it is closer to 0 dBm.
20. b--Lesson 2, DCAC 300-175-9 Extract, table 4, page 88 & e9.
All concerned will be careful that neither this solution nor
information concerning it comes into the possession of students, or
prospective students, who have not completed the work to which it pertains.
105
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