Select the input connector (front panel or rear
panel
AM IN
) that is connected to the external
signal source.
Press
On / Off
to turn AM on and off. Both the AM
status display and AM modulation status area will
reflect your selection.
Press
Log / Linear
to select the AM operating
mode. The AM status display will reflect your selec-
tion as XX dB/V (Log) or XX %/V (Linear).
Press
Edit Sens
to open the AM Sensitivity pa-
rameter, then edit the current value using the cur-
sor control key or rotary data knob or enter a new
value using the keypad and the appropriate termi-
nator key (
kHz/
µ
s/STEPS
for Linear;
MHz/ms/dB
for
Log). The AM Sensitivity range is 0 %/V to 100 %/V
in Linear and 0 dB/V to 25 dB/V in Log. To close the
open Am Sensitivity parameter, press
Edit Sens
or
make another menu selection.
Press
600
Ω
/ 50
Ω
to select the input impedance of
the input connector. The AM status display will re-
flect your selection.
Press
Front / Rear
to select the front panel or rear
panel
AM IN
connector. The AM status display will
reflect your selection.
Frequency
Modulation
Operating
Modes
The sweep generator has two FM operation modes—
Locked FM and Unlocked FM. In Locked FM mode,
frequency modulation of the output signal is accom-
plished by summing the modulating signal into the
FM control path of the YIG phase-lock loop. Maxi-
mum FM deviation is the lesser of
±
10 MHz or
Fmod x 300 for 1 kHz to 500 kHz rates.
In Unlocked FM mode, the YIG phase-lock loop is
disabled to allow for peak FM deviations of up to
100 MHz. There are two Unlocked FM modes—Un-
locked Narrow and Unlocked Wide.
In Unlocked Narrow mode, frequency modulation is
obtained by applying the modulating signal to the
fine tuning coil of the YIG-tuned oscillator. Un-
locked Narrow FM mode allows maximum devia-
tions of
±
10 MHz for DC to 500 kHz rates.
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.
NOTE
Refer to Appendix B, page B-5, for
the maximum FM deviation speci-
fications for 681X5B models.
3-62
681XXB OM
