TM 11-5820-803-12
-3
4.3 x 10 .
(2) Internal coder/decoder
on the data transmitted. Although the receiver detects
-6
the phase shifts, it cannot distinguish which phase
(3) External Viterbi coder/decoder 1.3 x 10 .
represents a ONE and which phase represents a ZERO.
The demodulated data processed by the receiver is as
Therefore, the only option which satisfies the
likely to be inverted as not differential coding may be
requirements is the use of an external (Viterbi)
used to resolve this ONE/ZERO ambiguity.
coder/decoder, KY-801/GSC.
b. The operation of a differential encoder is
illustrated in A, figure 2-6. A transition in the output data
2-5. Differential Coding
is produced for each ONE in the input data. No
a. The biphase PSK modulation technique
transitions are produced for the Zero's in the input data.
produces an ambiguity over the communications link.
The 70 MHz input to the receiver is switched back and
forth between two phases (fig. 2-2) depending
Figure 2-6. Differential encoding and decoding waveshapes.
2-7
