Amplitude Modulation Level Shifter; Auxiliary Output Amplifier; Amplitude Modulator - Wavetek 193 Instruction Manual

4-13
4.5.9 Amplitude Modulator
Refer to sweep/mod board schematic sheet 2. The
output amplifier U9 pin 2; the mode switch SW3-C
controls the dc offset. Refer to the table on the
schematic sheet 3. The auxiliary output signal feeds
both the AUX OUT BNC and MODE switch SW3-Aand
8 for sweep, frequency or amplitude modulations.
If the MODE switch is set to SET FREQ, SET START,
or SETCARRIER,both ends of the WIDTH/~F/~M are
shorted together, R108 has no affect. This biases the
Auxiliary output amplifiers output to a level dependent
upon the Mode SW3-Cselected: OVfor SET CARRIER
and SETSTART,and
+
SV for SET FREQ. This allows
setting of front panel controls for the generator board.
If the mode switch is set to SET ~F, SET WIDTH, or
SET ~M, a dc level, referenced to ground is con-
nected to the WIDTH/~F/~M control. This level
represents a dc equivalent of the modulating signal
and allows static set up conditions of the main
generator. The maximum dc level applied to the
WIDTH/~F/~M control depends on the mode selected
and SUPPRESSEDCARRIERswitch position, refer to
table 4-1.
When AUX GEN OFF is selected, the output from U10
pin 7 (LOOPSTOP)shuts off the current source in the
modulation generator VCG system.
Suppressed
Bias Amplifier Level
Carrier
Mode Switch Switch U10 Pin 1
U10 Pin 7
SET FREQ No affect
+5V + 10V
AUX GEN OFF
SET .iF
No affect -2.5V -5V
FM No affect OV
OV
SET START No affect OV
OV
SET WIDTH No affect -4.8V
-9.6V
SWEEP
No affect -2.5V -5V
SET CARRIER No affect
OV OV
SET .iM
Off +2.5V
+5V
On -2.5V -5V
AM No affect OV
OV
AUX OUT ONLY No affect
OV OV
Table 4·1. Bias Amplifier Levels Vs Modes
4.5.8 Auxiliary Output Amplifier
Refer to sweep/mod board schematic sheet 3. The
auxiliary output amplifier consists of a single amplifier
U9. The amplifier input signal originates at the sine
converter, square wave limiter, or modulation gener-
ator loop (triangle) and is selected by the function
switch to be routed through the Mode switch of the
modulation control switching to the WIDTH/~F/~M
control. The WIDTH/~F/~M control varies the level of
the auxiliary output signal. The output from U10 pin 7
provides dc offset to the inverting input of the auxiliary
4.5.7 Amplitude Modulation Level Shifter
The amplitude modulation level shifter sums inputs
from the modulation control switching (de reference
levels or ac waveforms), suppressed carrier switch
SW4 (dc reference level), and the AM IN 8NC J14 (an
external signal). This circuit shifts the dc level,
depending upon the position of the SUPPRESSED
CARRIERswitch, that drives the Amplitude Modulator.
sists of the MODE and SUPPRESSED CARRIER
switches.
The MODE switch is a four wafer switch. Wafer SW3-
A in AM and SET ~M routes either a modulating signal
(AM) or a dc level (SET ~M) from the auxiliary output
amplifier to the AM level shifter. Wafer SW3-8, when
MODE is set to SWEEP, SET WIDTH, SET START, FM,
SET ~F, and SET FREQ, connects either a modulating
signal (SWEEP and FM) or a dc level (SET WIDTH, SET
START, SET ~F, and SET FREQ) from the auxiliary out-
put amplifier to the SWEEP/FM IN at the main
generator VCG. Wafer SW3-C controls bias amplifiers
U10 pins 1 and 7, part of the auxiliary output amplifier;
table 4-1 shows the bias amplifiers output levels
relative to MODE switch settings. Wafer SW3-D con-
trols the input conditions, via the WIDTH/~F/~M con-
trol, for the auxiliary output amplifier: for AUX OUT
ON LY and AM SW3-D routes the waveform (FU NC) to
one end (ES) of the WIDTH/~F/~M control; for SET
~M, SET WIDTH, and SET ~F SW3-D grounds one end
(ES) of the WIDTH/~F/~M control; and for SET CAR-
RIER, SET START, and SET ~F SW3-D shorts out the
WIDTH/~F/~M control.
The SU PPRESSED CARRI ER controls the bias and
gain of the amplitude modulation level shifter. When
SUPPRESSED CARRIER is pressed, one section of
SW4 shorts out R118, this increases the gain of the
amplitude modulation level shifter, and removes
R126, which was in parallel with R86. Also, the other
section now supplies a
+
1SV bias when SET ~M is
selected.