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Radar System Engineering

Radar System Engineering

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146 C-W RADAR SYSTEMS [SEC. 58<br />

Modulation from the latter source is at the modulating frequency and<br />

low harmonics thereof. These spurious signals may be greatly reduced<br />

by two devices. First, one makes the mixer of Fig. 5.11 a balanced one<br />

—<br />

---ml<br />

FIG. 5.13.—The AN/APN-l frequency-modulatedradar altimeter, (Reprinted from<br />

Electronic-s.)<br />

(see Vol. 24) with the result that, if the balance is good, amplitude<br />

modulation from the transmitter balances out in the detector output.<br />

Second, the amplifier that precedes the limiter is given a response that is<br />

a rising function of frequency. The spurious signals, being largely of

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