2-34
However, the frequency spectrums are similar. Sideband distributions are similar, but not identical, since
the pulse transmitter in figure 2-30 is gated on and off instead of being modulated by a square wave as
was the case in view (D) of figure 2-29.
Remember, in pulse modulation the sidebands produced to accompany the carrier during
transmission are directly related to the harmonic content of the modulating wave shape. In figure 2-31,
(view A, view B and view C), observe the square and rectangular wave shapes used to pulse modulate the
same carrier frequency in each of the three views.
Figure 2-31A.—Varying pulse-modulating waves.
Figure 2-31B.—Varying pulse-modulating waves.
Figure 2-31C.—Varying pulse-modulating waves.
Let’s take note of some timing relationships in the three modulating sequences in figure 2-31:
the time for the rf cycle is the same in each case
the number of cycles occurring in each group is different
the ratio between transmitting and non-transmitting time varies
the transmitter produces an rf wave four times in view (A), three transmission groups in view (B),
and only two in view (C)
rf is generated only during the positive pulses
