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TO 31R2-2GRC171-2
TM 11-5820-815-14
NAVELEX 0967-LP-544-5010
produce a reference voltage across diode CR4 that
cut to the center of the uhf operating frequency. Refer to
biases Q1 to about 20 milliamperes. Thermistor RT12
A8HY1 and A8HY2 of figure FO-25. When terminals E2,
provides temperature compensation for the stage 4
E3, and E4 of A8HY1 are terminated into 50 ohms
linear rf amplifier.
(characteristic impedance of the quarter wavelength
lines), the input rf signal applied to terminal E1 divides
4-261.  The amplified output of Q1 is coupled to the
equally and appears at output terminals E3 and E4, 3 dB
stage 5 linear rf amplifier, Q2, through the impedance
down (half power) and 90-degree phase related.  No
matching network composed of capacitors C17, C18,
signal appears at terminal E2.  The isolation between
and C19, inductor L5, and resistors R18 and R19.
output terminals is approximately 25 dB. When two rf
Transistor Q2 is biased by base current supplied from
signals are simultaneously applied to terminals E3 and
bias network R13-R10-RT14-CR5 and applied to the
E4, the signals add together and appear at either
base of Q2 through inductor L7 and impedance network
terminal E1 or terminal E2 depending upon the 90-
Z2 (ferrite beads).  Resistor R10 is test selected to
degree phase relationship of the input signals. In the
produce a reference voltage across diode CR5 that
case of A8HY2 of figure FO-25, the rf signals add at
biases Q2 to about 20 milliamperes. Thermistor RT14
terminal E1 and cancel at terminal E2. If the loading at
provides temperature compensation for the stage 5
terminals E3 and E4 of A8HY1 becomes greater than 50
linear rf amplifier. The amplified output of Q2 is coupled
ohms, the reflected power that results from the mismatch
to the output of A3 through the impedance matching
adds together and appears at terminal E2. This reduces
network composed of inductors L8, L9, and L10 and
the power output at terminals E3 and E4 and increases
capacitors C20, C21, C22, C25, and C26.
the power at terminal E2. The hybrid coupler used in the
pin diode ALC attenuator of figure FO-28 uses this
4-262.  When the transmitter is unkeyed, the voltage
principle to attenuate the input rf signal.
applied to the +5-V dc switched input is reduced to 0 V
dc and the applied ALC voltage is increased to a high
4-259.  Refer to figure FO-28.  ALC voltage applied
positive value. This removes the bias voltage from Q1
through rf chokes L1 and L2 to the anode of pin diodes
and Q2 and causes maximum signal attenuation by the
CR1 and CR2 causes the resistance to ground at
pin diode ALC attenuator. The result of this circuit action
terminals E3 and E4 of HY1 to vary as a function of the
is to provide maximum attenuation in the rf signal path
ALC voltage. When the ALC voltage is a high positive
through A8A3.
value, the resistance of CR1 and CR2 is low causing the
resistance to ground at terminals E3 and E4 to be
4-263. RF DRIVER A8A4. Refer to figure FO-29. The rf
approximately 50 ohms (R2 in parallel with R3 and R4 in
input signal is coupled to the broadband rf power
parallel with R5). For this condition, the pin diode ALC
amplifier, Q1, through the gain slope pad composed of
attenuator provides maximum signal attenuation since
inductors L1 and L2, resistors R1, R2, and R3, and
almost all the rf input signal applied to terminal E1
capacitor C1. The gain slope pad compensates for loss
appears across resistors R2, R3, R4, and R5 and very
in power amplifier gain as the frequency of the applied rf
little appears at terminal E2.  The rf signal that does
input signal increases. The pad loss is about -5 dB at
appear at terminal E2 is shunted to ground through pin
225 MHz, -2 dB at 300 MHz, and -0.5 dB at 399 MHz. Rf
diode CR3 and capacitor C4.  Pin diode CR3 offers
power  amplifier  Q1  amplifies  the  rf  signal  to
minimum resistance because of ALC voltage applied
approximately 12-watt carrier power. Refer to paragraph
through HY1 from terminal E4 to terminal E2. As the
4-266 for a description of the rf amplifier.
ALC voltage decreases toward zero and becomes
negative, the resistance of CR1, CR2, and CR3
4-264.  RF AMPLIFIERS A8A5 AND A8A6.  Refer to
increases causing the resistance to ground at terminals
figure FO-30. The rf input signal is applied to terminal
E2, E3, and E4 to increase. As the resistance increases
E2 of hybrid HY1. HY1 splits the signal into two separate
from 50 ohms, the increase in reflected power resulting
signals that are 3 dB down from the input signal and 90-
from the mismatch appears at terminal E2. Thus, as the
degree phase related and applies them to two broadband
ALC voltage decreases, the attenuation of the pin diode
rf amplifiers, Q1 and Q2. The amplified outputs of Q1
ALC attenuator decreases causing the signal at terminal
and Q2 are applied to terminals E3 and E4, respectively,
E2 to increase.  This signal is applied to the base of
of hybrid HY2 where they are shifted back into phase
transistor Q1 of the stage 4 linear rf amplifier through the
and coupled to the rf output at terminal E2. Refer to
impedance matching network composed of capaci-tors
paragraph 4-266 for a description of the rf amplifiers.
C5, C6, C7, C8, and C9; inductors L3 and L4; and
resistor R7.
4-265.  Refer to figures FO-25 and FO-30.  Isolation
resistors A8R3 and A8R5 connected to rf amplifier A8A5
4-260. Transistor Q1 is biased by base current supplied
dissipate any reflected power that may result from
from bias network R11-R9-RT12-CR4 and applied to the
impedance unbalance at the input or output of
base of Q1 through resistor R8 and impedance network
Z1 (ferrite beads).  Resistor R9 is test selected to

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