3-11
SIGNAL MODULATION
The sweep generator provides AM, FM, and square wave modulation
of the output signal. All modulation modes—AM, FM, and square
wave—can be active simultaneously. The following paragraphs provide
descriptions and operating instructions for each modulation mode.
Use the Amplitude Modulation Mode, Frequency Modulation Mode,
and Square Wave Modulation Mode menu maps (Chapter 4, Figures 4-
9, 4-10, and 4-11) to follow the menu sequences.
Amplitude
Modulation
Operating
Modes
The sweep generator has two AM operation modes—
Linear AM and Log AM. In Linear AM mode, sensi-
tivity is 100%/V and the sweep generator accepts a
–1V to +1V input signal from an external signal gen-
erator. With a –1V input, the RF output shuts off ;
with a 0V input, the RF output (reference level) is
unchanged; and with a +1V input, the RF output is
100% (3 dB) higher than reference level. The ampli-
tude of the RF output changes linearly as the exter-
nal AM input changes.
In Log AM mode, sensitivity is 10 dB/V and the
sweep generator accepts a wider range of input sig-
nals from the external signal generator. For every –
1V input, the RF output level decreases by 10 dB;
for every +1V input, the RF output level increases
by 10 dB. The dynamic range of the of positive or
negative power levels depends on the sweep gener-
ator power level setting.
Providing
Amplitude
Modulation
To provide amplitude modulation, first set up the ex-
ternal signal generator, then connect it to either the
681XXA front or rear panel
AM IN
connector.
Next, press
MODULATION
. At the resulting menu
display, press
AM
. The External AM Status Menu
(shown below) is displayed.
LOCAL (FRONT
SIGNAL
PANEL) OPERATION
MODULATION
ERR
This error message is displayed
when the external AM modulating
signal exceeds the input voltage
range. The message “
Reduce AM
Input Level
” also appears at the bot-
tom of the AM status display. AM is
turned off until the modulating sig-
nal is within the input voltage
range.
681XXA OM
3-47
