TM 11-6625-333-15
FUNCTIONING OF EQUIPMENT
6-1. General
c. The dummy load has an swr of 1.1 to 1, or
less, at frequencies up to 30 megacycles. Capaci-
t o r s C2 and C3 provide balance and bypass rf
important consideration in transmission systems.
f r o m the insulated resistor mounting plates to
If the load and source are mismatched, part of the
g r o u n d . Capacitor Cl is connected to the input
power is reflected back along the transmission line
line to compensate for wiring inductance.
toward the source. This reflection not only pre-
vents maximum power transfer, but also can be
d. When the function switch is set to POWER,
responsible for erroneous rneasurements of other
power i s applied thrrough contacts 6 and 2 of
p a r a m e t e r s , o r even cause circuit damage in
switch S1 (A), to the dummy load consisting of
high-power applications.
r e s i s t o r s R1 through R12 and voltage-divider
resistors R20 and R21. Variable capacitor C4 is
b. The power reflected from the load interferes
c o n n e c t e d across resistor R20 and is used to
with the incident (forward) power causing stand-
a d j u s t the meter linearity at higher frequencies.
ing waves of voltages and current to exist along
F r o m the junction of variable capacitor C4 and
t h e line. The ratio of standing-wave maxima to
resistor R20, the circuit to meter Ml is completed
minima is directly related to the impedance mis-
t h r o u g h diode CR2, resistor R 2 2 , potentiometer
m a t c h of the load; therefore the standing-wave
R 2 3 , and contacts 8 and 12 of switch S1 (C).
r a t i o (swr) provides the means of determining
Capacitor C5 is a filter capacitor for diode CR2.
impedance and mismatch.
Potentiometer R23 is used to adjust meter linear-
ity at the lower frequencies. The lower scale of
m e t e r Ml indicates the RF power directly in
shown in figure 6-1, provides a noninductive
w a t t s , and the upper scale indicates the swr.
d u m m y load of 52 ohms and, when conneeted
Capacitor C8 is an RF bypass capacitor.
b e t w e e n the transmitter and its load, permits
d i r e c t readings of the transmitter power output
e. When the function switch is set to ADJUST,
and the swr between the transmitter and its load.
p o w e r is applied to the dummy 1oad described
in d above. It is also applied through contacts 12
a n d 9 of switch S1 (A) and resistor R13 to a
bridge circuit consisting of resistor R14, capacitor
C6, resistors R15, R16, and R17, and diode CR1.
a. The ME-165/G is used during preliminary
From the junction of diode CR1 and capacitor C6,
t u n e u p to eliminate transmitter damage because
the voltage is applied through filter resistor R18
of impedance mismatch, to permit optimum match
and capacitor C7 to ADJUST potentiometer R19.
between the transmitter and the antenna, and to
Potentiometer R19 controls the amount of voltage
keep the transmitter off the air until the tuneup is
applied to meter M1 and allows the meter to be
complete. During normal operation, the transmit-
adjusted to full scale for swr calibration purposes.
ter RF is applied directly through the ME-165/G
to the antenna.
f. When the function switch is set to SWR,
power is applied to the dummy load, resistor R13,
b. When function switch S1 is set to POWER,
and the bridge circuit as described in e a b o v e .
ADJUST, or SWR, 12 600-ohm resistors (Rl
Also, one leg of the bridge circuit (at the junction
through R12), connected in parallel, are used as a
o f resistor R14 and capacitor C6) is connected
dummy load. When the function switch is set to
t h r o u g h contacts 6 and 4 of switch S1 (C) to
O P E R A T E , the transmitter is connected directly
O U T P U T jack J2 and the normal transmitter
through the ME-165/G to the antenna (a a b o v e ) .
