Radar System Engineering

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712 RADAR RELAY [SEC. 17.9
Such a method would be extremely advantageous if multiple sets
of angular data were to be relayed.
3. Pulse methods are inherently more accurate than c-w methods
since they involve either” counting” or the measurement of time
probably the most accurate types of physical measurements that
can be made. Furthermore, no dependence whatever is placed on
the linearity of r-f modulators, amplifiers, detectors, etc., in contrast
to the c-w methods where all such devices must be extremely
linear and free from dk.tortion.
On the other hand, c-w methods involve somewhat simpler terminal
equipment than do the puke methods. They are also much less susceptible
to pulse interference, which is the type most likely to be met with at
most of the radio frequencies involved.
Comparison of Specijic Methods.—The specific synchronization
methods that have bee~ most thoroughly tested are—
1. The conveying of sine and cosine by pulses.
2. The conveying of angular increments by the modulator pulses.
3. The conveying of angular increments by the sinusoidally varied
pulse.
4. The method of phase-shifted pulses.
5. The conveying of sine and cosine by a-f signals of different frequencies.
Certain qualitative comparisons among these are possible.
The method of relaying angular increments by modulator-pulse timing
is by far the simplest if it can be used, which is only when the scanner
rotates very uniformly and can be exactly synchronized with the modulator.
Unfortunately, the tests of thk method were made in connection
with an airborne radar in which the scanning rate varied considerably;
hence appreciable inertia could not be used. Furthermore, multiplepulse
coding had not been adopted at that time. As a result, interference
led to somewhat erratic results. Since no opportunity has arisen for
testing with a proper radar and with coded pukes, it is difficult to make an
accurate assessment, but the comparative success under unfavorable
conditions indicates that when properly applied the method can be
satisfactory.
If the scanning is fairly uniform but cannot be synchronized with the
modulator, the method of the sinusoidally varied pulse (Sec. 17.5) gives
very satisfactory results with a minimum of complexity as proved by a
reasonable amount of testing (See. 17.15). This method is somewhat less
susceptible to interference effects than Method 2 since more data are
sent per radar cycle and since an extra pulse does not cause an irreversible
effect.
The method of relaying sine and cosine data by pulse-timing tech-