Radar System Engineering

496 THE RECEIVING SYSTEM—INDICA TORS [SEC. 137
Special amplifiers satisfying these requirements will be described later
in connection with specific applications. Many of these employ multistage
feedback.
13.7. The Generation of Rectangular Waveforms.-A rectangular
waveform is one whose outstanding characteristics are steep, alternately
positive and negative wavefronts with a space between (for example,
Fig. 13. 12). The term wilf include waveforms whose “tops” and
“bottoms” are not completely flat.
In some applications only tbe timing of one or both wavefronts
matters, the particular shape of the whole wave not being of interest;
(a)
Square wave oscillator
(no external stimulus)
(b) Flip-flop
(c)
3quaring amplifier
/
Trkwf ~
{ ‘e’p””’’nnn—r
I “-V-’
Sinusoid
‘es””’’J-Ll-L
Trigger#l ~
(d) Flopover Trlsser X2 ~
(e)Scaleof two
[’-n”J—uLr—u
(Trigger I I I I I
~ ‘es””” _nll——r
FIG. 13.12.—Response of various waveform generators.
in others the shape is also important. Among the latter are such applications
as the intensifying of cathode-ray tubes and the operating of
various electronic switches. Rectangular waves can be used for timing
purposes—for example, to initiate the generation of sharp pulses or otherwise
to initiate some particular event at the instant of occurrence of one
of the wavefronts.
The circuits that produce such waveforms can be divided into three
categories:
1. Those in which the waveform is produced without external
stimulus—that is, free-running oscillators (Fig. 13”13).
2. Those in which an externally induced departure from a stable state
with production of a wave front is later followed by a spontaneous
return which produces the wavefront of opposite polarity (Fig.
13.14). Such a device is called a “single stroke” generator or