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Radar System Engineering

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696 RADAR RELAY [SEC. 17.6<br />

station the two are separated by appropriate a-f falters, and the reference<br />

signal is passed through a frequency multiplier. The resulting sinusoid<br />

is then passed through a phase shifter controlled by a phase-sensitive<br />

Servomechatim as before. Although this method is simple, it places<br />

Modulated<br />

oscillator<br />

AudD<br />

oscillator<br />

I<br />

1: Filter<br />

o-~<br />

Video signals<br />

(a)<br />

,, B sin(2rrfot+@<br />

Phase<br />

comparator<br />

I<br />

, f, (~: byfo) Scan<br />

,<br />

4m-<br />

f2 (Mm. byf.)<br />

B sin ZrrJOt<br />

Video signals and trigger pulw<br />

(b)<br />

FIG. 176.-Phase-shift data transmission using two c-w subcarriers.<br />

+<br />

To indicators<br />

severe requirements on the audio filters. Because of their harmonic<br />

relationship, the sinusoids must be kept extremely pure, and furthermore<br />

any relative phase shifts introduced by the filters (or other circuit components)<br />

must be extremely constant with time. This is very di5cult to<br />

assure in a-f filters if they are subjected to changing temperatures.

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