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Model 492A/494A
SECTION I
GENERAL INFORMATION
Section I
Paragraphs 1-1 to 1-4
1-1. DESCRIPTION.
1-2. The
t$
Models 492A and 494A Traveling Wave
Amplifiers are broadband, linear amplifiers provid-
ing adjustable amplification up to at least 30 db, be-
tween 4 and 12.4 gc, and have a maximum power out-
put of at least 20 milliwatts to an external load of 50
ohms.
The frequency range of the
t$
Model 492A is
4 to 8 gc; the frequency range of the Model 494A is 7
to 12.4 gc.
These traveling wave tube (twt) ampli-
fiers are designed to be used also as buffer amplifiers
or modulators for any signal within their frequency
range.
As buffers, their input impedances remain
constant with any reasonable load change at the output
terminal; the attenuation between input and output sig-
nals is at least 60 db, minus the gain of the amplifier.
As modulators, they can be used
to
amplitude, fre-
quency, pulse, or phase modulate the signal being
amplified with no interaction on the signal source.
The gain and power output of the amplifiers are con-
tinuously adjustable by the front panel
GRID
BIAS con-
trol.
Hum and spurious modulation generated within
the amplifiers are at least 45 db below the output sig-
nal level and the noise figure is less than 30 db.
1-3. The
t$
Models 492A and 494A Traveling Wave
Amplifiers, amplify any type of
rf
signal: cw, swept,
sine-modulated, pulsed, multiple signals on different
frequencies, etc. A twt amplifier used as a modulator,
in conjunction with a signal generator, can be used to
amplitude modulate an
rf
carrier to approximately 30%
with less than 2.5% harmonic distortion and up to 50%
with less than 5% distortion.
Amplitude modulation
sensitivity is approximately 1 db/volt. Pulse modula-
tion is excellent; the rise time is less than 15 ns.
Phase modulation up to 360
0
with less than 1 db
amplitude modulation is also possible.
Wide-band
frequency modulation is simulated by a step-wise phase
modulation described in section
Ill.
1-4. The front panel meter is provided for checking
and adjusting electrode currents in the traveling-wave
tube.
The meter helps to obtain desired operating
characteristics during normal operation of the ampli-
fier and also assists with preventive maintenance and
troubleshooting.
An anode voltage adjustment on the
instrument chassis prOVided to adjust the cathode
current of the twt back to normal due to tube ageing.
)
00144-2
Figure 1-1. Model 492A Traveling Wave Amplifier
1-1
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