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Radar System Engineering

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666 MOVING-TARGET INDICATION [SEC. 16.17<br />

by radar receivers. It will be noticed that several extra stages are necessary<br />

to obtain this type of limiting. The coherent oscillator circuit has<br />

already been described. The function of the “coherent oscillator locking<br />

test” channel will be discussed in Sec. 16.21.<br />

.—— ————————.——.<br />

To , I<br />

normal Lownoise I<br />

amplifier<br />

receiver<br />

I<br />

L—––R:m~eYYl@~: ___ ~ =<br />

S,gnal<br />

mixer<br />

I gating system<br />

——— —— —________<br />

FIQ. 1630.-Block diagram of a typical MTI receiver: i-f limiting; balanced detector;<br />

intermediate frequency 30 Mc /8ec; l-p.sec pulBes.<br />

Figure 16.31 shows the circuit of the balanced detector, which converts<br />

phase changes at the input into amplitude changes at the output<br />

with a fair degree of linearity. 1<br />

I The thsory of the circuit is given in Vol. 23, Chap. 22.

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