RF Level
SMIQ
1125.5555.03
E-8
2.50
2.5.2
Interrupt-free Level Setting
In the ATTENUATOR MODE FIXED and ATTENUATOR MODE ELECTRONIC operating modes, level
settings are carried out without interruption. The attenuator is switched electronically rather than
mechanically.
The MODE FIXED variation range is somewhat over 20 dB, the variation range of MODE ELECTRONIC
over 90 dB. In case of over- or underranging of the normal variation range, level errors strongly increase
and an under/overrange warning is displayed. At high attenuation values the spectral purity of the output
signal is degraded.
The ATTENUATOR MODE ELECTRONIC mode is only possible with level control switched off. The
ALC OFF mode is automatically set to TABLE.
Note:
To ensure highest level accuracy in ATTENUATOR MODE ELECTRONIC mode, the self
calibration routines ALC TABLE and LEV ATT should be called up in the UTILITIES -
CALIB menu after temperature variations of more than 5 degrees.
The MODE ELECTRONIC cannot be used either simultaneously with the SLOT
ATTENUATION function of the digital standards. This applies to all TDMA standards. The
MODE ELECTRONIC cannot be used either simultaneously with the DIGITAL MOD -
POWER RAMP CONTROL - ATTENUATION function.
2.5.3
Switching On/Off Internal Level Control
The LEVEL - ALC menu allows the level control to be switched on and off for special applications. In the
normal operating mode for CW, AM and FM(PM), level control is switched on so that an optimum level
accuracy is obtained. For vector modulation or digital modulation, level control must normally be off. In
this case the SAMPLE&HOLD or the TABLE mode can be selected instead.
In the SAMPLE&HOLD mode the level is recalibrated after each level or frequency setting. To do this,
CW is selected for a short period of time, level control is switched on and the level control held at the
value attained. If this calibration procedure is not desired, the TABLE mode (level control voltage taken
from a table) can be selected. In this mode the correction values required after a frequency or level
change are obtained from a table. With the LEARN TABLE function called up, a new table can be
prepared without any additional measuring instruments being required.
The preset level control is AUTO. Level control in this mode is automatically adapted to the operating
conditions. For special applications, level control can be held in the OFF or ON state. Level control OFF
is useful for improving the intermodulation suppression in multi-signal measurements in the CW mode.
The ON setting is recommended if vector modulation or digital modulation with a constant envelope
curve is required.
