ANALOG MODULATION MODE
3-79
Extended hysteresis
Pressing the
[Extended]
soft key toggles the status (Enable/Disable) of extended hysteresis. When
enabled, this provides an electronic level function which uses the internal D/A converter, rather
than the attenuators, to provide an uninterrupted (glitch-free) level control. This increases the
electronic level control range to +12 to -18 dB. A
+HYST
or
-HYST
message is displayed on the
Sig Gen
menu to indicate when in hysteris and in which direction.
During normal operation the RF output is controlled as shown in Fig. 3-77 by electronically
controlling the output level over a limited range (normally approximately 0 to +6 dBm) and
switching in 6 dB attenuator pads to provide lower RF levels.
When the hysteresis function is enabled and a keyboard entry of the RF level is made, the signal
generator sets the level in the normal way. However, when the rotary control is enabled and used
to adjust the RF level, the normal attenuator changes are suppressed. When the level is increased,
the attenuator change is suppressed for 6 dB above the normal range and
+HYST
is displayed.
Similarly, when the level is reduced attenuator changes are suppressed for 12 dB below the normal
range and
-HYST
is displayed. When the extended hysteresis range is exceeded the attenuator and
the electronic control are reset to values corresponding to the normal operation of the generator.
An example of extended hysteresis operation is shown in Fig. 3-78.
With the rotary control in use in the hysteresis range of operation, the generator can be instructed
to set the RF level to the same value, but set using the [V], [mV], [
μ
V] or [dB] keys. This is a
useful facility if the user is investigating squelch systems and wants to ensure that varying the
level around the current value will not result in an attenuator change.
Requested output level
RF output before attenuator
Attenuator setting
+13 dBm
C0956
+13 dBm
0 dBm
0 dB
-6 dBm
0 dBm
+6 dBm
6 dB
-12 dBm
12 dB
-18 dBm
18 dB
24 dB
-24 dBm
Fig. 3-77 Normal signal generator level control operation