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|  C1302. When the operating fre-
12. Input Circuit
quency is lowered and the coupling
Received rf signals are fed to antenna
decreases, the impedance of ca-
relay K101 from the antenna through the
pacitor C1302 increases to com-
pensate for the decreased current
K101 is deenergized on receive, contacts
flowing through the diode load.
2 and 3 of relay K101 are closed, and the
Thus, capacitor C1302 provides a
rf signal is coupled to parallel-tuned tank
constant meter current for any
circuit Z101 through coupling capacitors
given transmitter output power
C106 and C108. Resistor R117 provides a
over the frequency range from
dc path to ground for static charges de-
225.0 to 399.9 mc.
veloped on the antenna. The parallel-
(6) The voltage drop developed across
tuned tank circuit consisting of Z101 and
resistor R1302 by the rectified rf
C107 provides a high impedance to rf sig-
current is coupled to the meter
nals in the 225.0- to 399.9-mc range.
circuit through calibrating resistor
R1301. The value of resistor R1301
is selected to obtain a PWR meter
indication 60 percent of full scale
for 16 watts output power at
a. Capacitor C110 couples the signal
319.9 mc.
voltage developed across Z101 and C107
to the cathode of grounded grid first rf
c. Directional Coupler B.
(1) The directional coupler circuit
amplifier V102. The cathode circuit con-
which includes coupling element B
sists of a Z102, a parallel-tuned circuit,
operates on the same principles
and cathode bias resistor R122. The tuned
described above. The circuit com-
circuit is resonant in the 225.0 to 399.9-
ponents associated with coupling
mc range and provides a high impedance
element B are located physically
for the rf signal. Capacitor C112 grounds
rf at the grid of V102. Resistor R104 con-
opposite to those associated with
coupling element A. Thus, the re-
nects the grid of V102 to the rf avc bus
sultant rf current induced in coup-
and with capacitor C109, isolates the rf
ling element B by the reflected
signal from the rf avc bus.
wave is rectified by diode CR1302
b. The +125-volt dc plate voltage is sup-
and metered to indicate reflected
plied to the plate of V102 through plate
power (SWR). The rf current in-
load L105 and plate voltage dropping re-
duced by the incident wave is ab-
sistor R116. Capactior C113 bypasses rf
sorbed by resistor R1303.
signals from the +125-volt dc supply. The
(2) Capacitors C1303 and C1304 and
rf signal is amplified by V102 and coupled
resistors R1307 and R1308 per-
by capacitor C114 to the parallel-tuned
form the same circuit functions as
tank circuit Z103 and variable capacitor
the corresponding components in
C115. The parallel-tuned tank circuit
the directional coupler circuit
serves as a high coupling impedance for
which includes coupling element A.
the rf signal.
Resistor R1308 has the same value
as resistor R1301.
a. Coupling capacitor C117 couples the
rf signal voltage developed across Z103
On receive, antenna relay K101 is de-
to the cathode of the second rf amplifier
energized and first and second rf ampli-
V103, a grounded grid amplifier. The
fiers V102 and V103 amplify the received
cathode circuit consists of Z104, a paral-
rf signal. First receiver mixer V104
lel-tuned circuit which is resonant in the
heterodynes the rf signal with the uhf in-
225.0- to 399.9-mc range and cathode bias
jection frequency to obtain the first if.
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