c. After it is amplified, the applied pulse is fed to a delay line that
delays the pulse by about one-half a microsecond. The applied pulse reaches
the screen one-half a microsecond after the sweep starts across the face of
the scope.
So the complete applied pulse, including its leading edge,
appears on the screen. Figure 40 shows the delayed pulse on the face of the
scope.
Figure 40.
Delayed Pulse on Scope.
21. Delay lines are used in time division multiplexing.
a. Time division multiplexing (TDM) is a system of communications that
allows the transmission of many messages over a single RF carrier. One TDM
system replaces many single-channel transmitters.
This is done by
converting up to twenty-three channels of audio information into a single
pulse-position-modulated (PPM), time-division-multiplexed (TDM) pulse train.
The train is then fed to an RF transmitter which transmits the signals to
the desired location. At the receiving end, the pulse train is demodulated
and the twenty-three channels of audio are relayed to their proper
destinations.
b. The block diagram in Figure 41 shows how delay lines separate the
pulses in a TDM transmitting set. The master pulse generator feeds a pulse
to two stages as follows:
(1) The sync shaper stage widens the pulse for synchronizing the
receiving multiplexer with the transmitting multiplexer.
(2) Then, the delay line sections in each channel delay the pulses
before they are modulated. There are twenty-three delay line sections, one
for each channel.
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