Square Wave
Modulation
Operating
Modes
The 681XXA provides square wave (pulse) modula-
tion of the output signal using modulating signals
from either its internal square wave generator or an
external signal generator.
The sweep generator’s internal square wave gener-
ator outputs modulating signals of 400 Hz, 1 kHz,
7.8125 kHz, and 27.8 kHz. The modulating signals
are selectable from a menu.
The 681XXA accepts modulating signals from an ex-
ternal signal generator that are TTL-compatible
with the minimum pulse width of 5
µ
s.
Providing
Square Wave
Modulation
The following are the menu selections necessary to
provide square wave (pulse) modulation of the out-
put signal using a modulating signal from both the
internal and external sources.
Press
MODULATION
. At the resulting menu dis-
play, press
SqWave
. The Square Wave Status
Menu (shown below) is displayed.
This menu contains the square wave status window
that shows the current menu selections. This menu
lets you perform the following:
Turn square wave modulation on/off.
Select Internal or External source for the
modulation signal.
Select the polarity of the signal (High or Low)
that turns the RF on.
Go to an additional menu (to select the fre-
quency from the internal source or to select
the front or rear panel input connector).
LOCAL (FRONT
SIGNAL
PANEL) OPERATION
MODULATION
681XXA OM
3-51
