TM 11-5840-281-35/1
Amplifier AM-3338/TPN-8 decreases at a logarithmic
as the i-f signal going through the stages, and the pulses
rate as the input signal amplitude in- creases. Because
from all of the detectors are coincident going into
of its gain characteristics, log Intermediate Frequency
summing resistor R3650; therefore, the iagc pulse is not
Amplifier AM-3338/ TPN-8 cannot saturate. When EL
longer than the i-f signal producing the pulse.
TARGET control R620 on Control-Indicator C-6988/TPN-
(5) The detected log video output is amplified by
18 is at its extreme NARROW position, a given block of
video amplifying hubes V3607 and V3608 and the iagc
ground clutter will produce a log Intermediate Frequency
pulses are delivered to Intermediate Frequency Amplifier
Amplifier AM3338/TPN-8 output which will consist of
AM-3339/TPN-8 by cathode follower tube V3609. The
many signals of various widths. This output becomes the
nominal amplitude of the iagc pulses is about 4.5 volts
iagc pulse to Intermediate Frequency Amplifier AM,3339/
for a strong clutter signal. The gain of video stage tube
TPN-8, and will reduce the gain of the i-f the strip for
V3608 is adjusted by SLOPE ADJ control R3661. This
most of the ground clutter except when the beam of
control has its greatest effect at the end of the log curve,
Antenna AS-1291/TPN-8 is vertically centered on the
and is used to control the maximum signal output (about
target. When EL TARGET control R620 is at its WIDE
1.5 volts on strong clutter.) CROSS- OVER ADJ control
position, there is no output from log Intermediate
R3645 shows more effect on the first portion of the
Frequency Amplifier AM-3338/TPN-8; therefore wider
curve, or for low amplitude i-f signals, and is adjusted to
target blips, corresponding to the full vertical beam-
reduce the noise peaks on the baseline.
width, will be displayed.
(2) Input transformer T3601 in log Intermediate
(6) The supply voltage lines in all of the i-f
Frequency Amplifier AM-3338/TPN-8 is similar to input
amplifiers are decoupled between stages by lc filters.
transformer T301 in Intermediate Frequency Amplifier
The inductive element of these filters consists of ferrite
AM-3339/TPN-8 of the sum channel. It is followed by six
beads on the connecting wire between capacitors or
double-tuned stages. Each stage includes its own video
circuit components. These ferrite beads are designated
detector and limiting diodes. The video detector outputs
as FB1, FB2, etc. The ferrite bead provides the desired
are summed across resistors R3609 and R3650 to
inductive reactance, and the magnetic material
produce the log output. A weak, barely detectable signal
necessary to decrease the chances of stray coupling
would pass through and be amplified in turn by all six i-f
from the fields of the normal filter coils.
stages 'and produce a video signal at the iagc pulse
j
Video Amplifier Circuit (Fig. 7-7.and 7-41).
output of about 0.6-volt peak. A strong signal, nearly
saturating Intermediate Frequency Amplifier AM-
The functions of video amplifier are to amplify the video
3337/TPN-8, would have sufficient amplitude to be
signals, to provide ftc of the video signal when selected,
detected by first detector diode CR3601, and be passed
and to provide a low-impedance output. The ftc function
cancels all but the first 0.2 sec (narrow pulse) or 0.8
on through to the output at about 0.6-volt peak.
sec (wide pulse) of any block of video. Short pulses (0.2
(3) A signal (such as from an echo box) which at
first was strong and then decayed logarithmically would
or 0.8 sec or less) on top of longer blocks will be
produce a constant amplitude output. Since all signals,
passed on through the amplifier.
weak and strong, produce a relatively large output, the
video waveform at the iagc pulse output looks like a
(1) The detected video input is impedance
series of many gate pulses.
matched to transistor Q1403 through emitter-follower
(4) There is about a 0.02 sec inherent delay in
transistors Q1401 and Q1402. The base of Q1401 is
each stage of the amplifier, which tends to stretch the
clamped to approximately 0 volt by diodes CR1401 and
pulse. Chokes L3608, L3610, I3612, L3614, L3616, and
CR1402. This clamp prevents the base of emitter-
L3618, with their associated capacitors C3610, C3615,
follower transistor Q1401 from going negative, thereby
C3620, C3627, C3632, and C3640 in the summing line,
eliminating any unwanted negative excursions from the
delay the signal about 0.02 sec each, and are used to
detected video. When the ftc function is not being used,
compensate for the inherent delay in each amplifier
Q1403 provides an extra emitter-follower isolation sage.
stage. The signal from each detector receives the same
delay
(2) The positive-going input is applied to the
base of emitter-follower transistor Q1401. The video
signal passes through emitter followers
2-20
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