HP 8920A, User Manual

Page: 416 / 658

416
S:\HP892XX\USRGUIDE\manual\encoscrn.fb
Chapter 10, Signaling Encoder (AF Generator 2)
MPT 1327 Encoder
Table 11 describes the signaling encoder as it is changed between the various test modes.
Particular reference is made to how the control and traffic channel message structures are
started and stopped.
A. Start the control channel with a 6-bit LET, PREAMBLE, and SYNC. For the first ad-
dress codeword (before the repeating SYS, CCS, PREAMBLE, PARITY, CODE-
WORD, PARITY structure), the codeword comes from the second half of the filler (or
message) buffer timeslot 1.
B. Start the traffic channel with a LET, PREAMBLE, and SYNT. Again the first codeword
is taken from the timeslot 1 entry.
C. Turn on 1200 Hz sine wave starting at 0
°
phase.
D. Turn on 1800 Hz sine wave starting at 0
°
phase.
E. Turn on “dotting” with a 1 symbol. The starting phase may be 0
°
or 180
°
.
F. Continue to generate the control channel until the end of the filler buffer (and message
buffer if messages are present) then produce a hang-over bit and stop. The hang-over
bit repeats the last bit of the transmission.
G. Continue to generate the traffic channel until the message is completed then produce a
hang-over bit and stop. The hang-over bit is followed by one “off” bit before the next
sequence begins.
H. Stop control channel generation after the next bit.
I. Stop traffic channel generation after the next bit.
J. Turn off 1200 Hz sine wave on completion of the next symbol.
K. Turn off 1800 Hz sine wave on completion of the next symbol.
L. Turn off “dotting” on completion of the next 1010 symbol. Dotting is sent as the se-
quence 1010 rather than 10. This makes the trace on the internal scope stable when trig-
gered by the encoder since every second 1 starts on the opposite phase.
M. Make a phase continuous transition to 1200 Hz on completion of the next symbol.
N. Make a phase continuous transition to 1800 Hz on completion of the next symbol.
O. Make a phase continuous transition to “dotting” (starting with a 1 symbol) on comple-
tion of the next 1010 sequence.
Table 11 Signaling Mode Transitions Table
To From Off Control Traffic 1200Hz 1800Hz Dotting
Off — A B C D E
Control F — H then B F then C F then D F then E
Traffic G I then A — G then C G then D G then E
1200Hz J J then A J then B — N O
1800Hz K K then A K then B M — O
Dotting L L then A L then B M N —