Radar System Engineering

488 THE RECEIVING SYSTEM—INDICATORS [SEC. 13.4
magnetic field in the same direction as the magnetic axis of the transmitter
rotor coil. There will be induced in the receiver rotor a voltage
proportional to V sin (t% – %) where 131and 02 are the respective orientations
of thetwo rotors. Ifthereceiver isprovided with a second rotor
coil orthogonal to the first, it will experience a voltage proportional to
Vcos (0, – e,). Thus the two devices together “resolve” the original
voltage in terms of the difference of the two angles. A resolver with a
multiple-phase rotor is known as a “differential” synchro or resolver.
It is used in reducing data from relative to true bearing (one synchro
=0
1
v
/1
0,
L_- -
KV Sin tll
r--l
Ststor
(a)
I
KV sin (@92)
1
1 I
(b) KV COS (61-82)
FIG. 13.6.—Two-phase synchros. (a) Two-phase .ynchro; (b) differential synchroremlver.
being driven by a compass), and in enabling an operator to shift the
scanner reference angle for purposes of sector selection.
The 2-phase resolver has been used in nearly all practical applications
of the resolved-sweep technique to “electronic” PPI’s and RHI’s (Fig.
12.3) andinmany applications where pre-time-base resolution is applied
to these displays.
For many purposes a 3-phase rather thana 2-phasel device is used.
If equal loads are applied across the three phases the sum of currents in
thethree stators iszero. Thus, ifthisrestriction isimposed, three brushes
and three wires can be eliminated by making a Y connection. If a
synchro with a 2-phase rotor is used as a receiver, its induced voltages
1In this sensethe word “phase” refersto rotationof the rotor ratherthan to the
internalphase of any signalbeing transmitted.
*