attenuator is the generator output when the FREQ.
decoupling resistor R44 to the tap on coil L3. Screen grid
RANGE-MC switch is in the 200-400 mc position.
voltage for V6 is supplied through voltage dropping
b. At the high operating frequencies of the third
resistor R43 and is bypassed by capacitor C22. The
doubler, slight changes in component values have a large
output from V6 is fed to the grid circuit of rf amplifier V7
effect on the response of the stage. Trimmer C46 adjusts
through R46 and coupling capacitor C26 (fig. 12).
the plate tank for maximum output. This trimmer is
adjustable at the front-panel 200-400 MC TRIMMER
45. Rf Amplifier V7 and Variable Attenuator
first doubler circuit with the two following exceptions: The
plate circuit is tuned to the frequency applied to the grid. 48. Output Indicator Circuit
a. The output indicator circuit (ng. 14) is a bolometer
A portion of the rf amplifier output is coupled to the
variable attenuator and is the signal generator output bridge circuit which uses a galvanometer to indicate
bridge balance.
signal in the 500-100 mc range.
b. Galvanometer M2 has its mechanical zero at
b. The variable rf output attenuator E2 is made up of
coupling coil L15 and impedance transfer network R50, center scale and is connected between the movable arm
C31, and L16. The signal developed across coil L16 is of potentiometer R130 and the junction of the other two
transferred by 50-ohm coaxial cable W3, to the 50-100 arms of the bridge. One arm of the bridge consists of
mc contact of FREQ. RANGE-MC selector S5 (fig. 44). thermal compensating resistor RT3 and potentiometer
The output signal level at connector J1 (fig. 44) is R129. A second arm of the bridge consists of bolometer
determined by the degree of coupling between L15 and RT4 which is returned to ground through attenuator coils
L14. The three variable attenuators E2, E3, and E4 are L16, L19, L22, and resistors R128 and R126. The other
ganged, and the selected attenuator is connected to two arms of the bridge are the portions of each side of the
movable arm of potentiometer R130. The circuit operates
output connector J1 through switch S5.
c. A portion of the output of V7 also is coupled as follows: Direct current from the plate supply flows
through resistor R53 and capacitor C33 (fig. 13) across through all arms of the bridge; rf currents flow only
through the bolometer arm of the bridge. Capacitor C96
grid resistor R54 to the grid of second doubler V8.
by-passes one end of RT4 to ground for rf currents. The
bridge is balanced by adjusting potentiometer R130 for an
46. Second Doubler V8
a. The second doubler circuit (fig. 13) is similar to output of 100,000 microvolts across a 50-ohm load at RF
the rf amplifier except that its plate circuit is tuned to OUTPUT receptacle J1. With the bridge balanced, a
twice the frequency of the grid input signal. The plate decrease in the rf input level causes the bolometer
circuit consists of coil L17, tuning capacitor C36A and resistance to decrease.
A decrease in resistance
C36B, and trimmer capacitors C37 and C39. The tank unbalances the bridge and causes the galvanometer to be
circuit is tunable through the 95- to 200-mc frequency deflected below center scale. An increase in the rf level,
range. The second doubler variable attenuator E3 is increases the bolometer resistance and unbalances the
ganged to the one in the rf amplifier. It consists of coils bridge deflecting the galvanometer needle above center
scale. The OUTPUT control dial is calibrated at each use
L18 and L19, capacitor C35, and resistor R56.
b. A portion of the output of V8 also is coupled by adjusting the OUTPUT control for a center scale (SET
through capacitor C38 across grid resistor R59 to the grid TO LINE) reading on the OUTPUT meter and setting the
movable index on the OUTPUT dial to 100,000
of third doubler V9.
microvolts. The rf output of the generator now may be
read directly in microvolts or dbm from the OUTPUT
47. Third Doubler V9
c. Potentiometer R129 permits the temperature
second doubler circuit except that the tuned plate circuit
and attenuator E4 operate in the 200-400 mc range. The compensating characteristics of that arm to be varied
attenuator is ganged with the attenuators in the rf even though the characteristic of temperature
The output of this compensating resistor RT3 is fixed
amplifier and second doubler.
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