TM 11-5821-284-34
g. Servo Motor Control Circuit. The servo
power is applied to the antenna.
k. Manual Override Logic. The manual over-
motor control circuit receives inputs from the servo motor
ride logic is provided to enable tuning of the antenna
sequencing logic and provides a ground for the +28-volt
without applying transmitted RF power.
dc power source used to drive the servo motor.
h. Servo Motor. The servo motor turns in 15-
l.
Homing Logic. The homing logic provides a
degree steps and adjusts the series variable capacitor to
signal to return the series variable capacitor to minimum
tune the antenna circuit to resonance near the
capacitance after it has reached maximum capacitance.
transmitted frequency.
m. Tuning Indicator Drive. The tuning indicator
i.
Antenna Circuit. The antenna circuit is
drive circuit receives an input signal from the sequential
pulsing logic and amplifies it to a 3- to 5-volt square-
tuned to resonance by the series variable capacitor and
wave output for use in an external tuning indicator.
by a small series variable inductance provided by the fine
n. Voltage Divider. The voltage divider circuit
tune circuit.
j.
Transmit/Receive
Logic.
The
converts the +28-volt dc input to proper input voltages for
the circuits of the antenna.
transmit/receive logic (RF-on) circuit inhibits the servo
rotation logic against tuning to erroneous signals. The
RF on circuit enables the tuning circuits when transmitter
Section II. SCHEMATIC DIAGRAM ANALYSIS
In the detailed theory of operation discussion, the term logic "1" means a positive potential (approximately
+3.5 volts dc) and the term logic "0" means a near ground potential (approximately +0.2-volt dc). Refer to
the schematic diagrams, figures 5-6, 5-7, for overall circuit discussion and to figures 2-2 through 2-9 for
simplified diagrams of the individual circuits.
addition of the induced voltage (e2) and the sampled
2-4.
Phase Discriminator Analysis
voltage (e6) in circuit number 1 creates a result-ant
(figs. 2-2, 2-3)
voltage (e4). The vector addition of the induced voltage
The phase discriminator develops a dc error signal that
(e6) and the sampled voltage (e6) in circuit number 2
is proportional to the phase shift between the RF line
creates a resultant voltage (e4). The algebraic sum of
current.
the two resultants, (e4 and e5), is the error signal output.
a. The impedance presented to the RF signal
When the impedance is restrictive, the magnitude of the
by the antenna is either resistive, capacitate, or
resultant voltage (e4) is equal to the resultant voltage
inductive, depending on the signal frequency and its
(e5). The voltages are of opposite polarity and cancel
relation to the resonant frequency of the antenna. When
each other so the error signal is zero. When the
the RF signal frequency is below the resonant frequency
impedance is capacitive, the resultant voltage (e4)
current (iL) leads line voltage (eL) and the error signal
increases in magnitude. The algebraic sum of (e4) and
developed is positive. When the RF signal frequency is
(e5) causes a positive error signal output. When the
above the resonant frequency of the antenna the
impedance is inductive, the resultant voltage (e4)
(eL) and the error signal developed is negative. When
decreases in magnitude. The algebraic sum of (e4) and
the RF signal frequency is the same as the resonant
(e5) causes a negative error signal output.
frequency of the antenna the impedance is resistive.
Line current (iL) is in phase with line voltage (eL) and
CR1 and filtered by FL1. Resultant voltage (e5) is
there is no error signal developed.
rectified by diode CR2 and filtered by FL5.
The
b. The phase discriminator is divided into two
rectification and algebraic sums of the resultant voltages
circuits. Circuit number 1 consists of points B, C, E, and
create a dc error signal output proportional to the phase
F. Circuit number 2 consists of points A, D, E, and F.
shift between RF voltage and RF current.
The line voltage (eL) is sampled, with no phase shift,
through the capacitance between the windings of coil L3
and the transmission line. The voltage induced in L3 is
90 degrees out-of-phase with line current (iL). The vector
2-2
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