FM IN: Accepts an external modulating signal
to produce FM on the RF output. FM sensitivity
and input impedance (50
Ω
or 600
Ω
) are select-
able via front panel menu or GPIB. BNC con-
nector.
IN: Accepts an external TTL level signal
to square wave (pulse) modulate the RF out-
put. BNC connector.
EXT ALC IN: Provides for leveling the RF out-
put signal externally with either a remote de-
tector or a power meter. Connector accepts a
positive or negative 0.5—500 mV signal from
a remote detector or a
±
1V signal from a re-
mote power meter. BNC connector.
Line Fuse: Provides over-voltage/current pro-
tection for sweep generator circuits during op-
eration and standby. Unit requires a 5A, slow
blow fuse for 110 Vac line voltage or a 2.5A,
slow blow fuse for 220 Vac line voltage.
LINE SELECT Switch: Provides selection of
110 or 220 Vac line voltages. When 110 Vac is
selected, the 681XXB accepts 90-132 Vac, 48-
440 Hz line voltage; when 220 Vac is selected,
the 681XXB accepts 180-264 Vac, 48-440 Hz
line voltage.
Input Line Voltage Receptacle: Provides for
connecting line voltage to the 681XXB.
IEEE-488 GPIB: 24-pin connector that pro-
vides for remotely controlling the sweep gener-
ator from an external controller via the IEEE-
488 bus (GPIB). A pinout diagram for this con-
nector is shown in Figure A-3.
SERIAL I/O: Provides access to two RS-232
terminal ports to support service and calibra-
tion functions and master-slave operations.
RJ45 connector.
DWELL IN: Accepts an external TTL low-level
signal to stop the sweep in both analog- and
step-sweep modes. The sweep resumes when
the signal is removed.
V/GHz OUT: Provides a reference voltage rela-
tive to the frequency of the RF output (see
table below). BNC connector.
PEN LIFT OUT: Provides relay contacts for
lifting and dropping a chart recorder’s pen dur-
ing bandswitch points and sweep retrace.
Selection of normally-open or normally-closed
relay contacts can be made from the front
panel menu. BNC connector.
MARKER OUT: Provides a –5V or +5V output
at each frequency marker if video markers
have been selected. Selection of signal polarity
can be made from the front panel menu. BNC
connector.
RETRACE BLANK OUT: Provides a –5V or
+5V output during sweep retrace. Selection of
signal polarity can be made from the front
panel menu. BNC connector.
Figure A-1.
Rear Panel, Series 681XXB Synthesized Sweep Generator (2 of 2)
REAR PANEL
CONNECTORS
10
11
12
15
16
9
8
Model Number
V/GHz Output
68137B, 68145B, 68147B
1.0V/GHz
68153B, 68155B, 68159B
0.5V/GHz
68163B, 68163B, 68169B
0.5V/GHz
68175B, 68177B
0.25V/GHz
68185B, 68187B
0.25V/GHz
68195B, 68197B
0.25V/GHz
7
13
14
17
18
19
681XXB OM
A-3
