HP 8360 - Manual (Page 151)

Note Two terms are used in the following discussions: power output and
ALC level. Power output means actual output power including the
effects of the attenuator. ALC level means power levels before the
attenuator. In synthesizers without attenuators, these two terms are
equivalent.
Internal Leveling Leveling Mode
L e v e l i n g P o i n t
In this configuration (Figure A-l), power is sensed by a detector
internal to the synthesizer and a dc output from this detector is fed
back to the
Level Control Circuits.
The ALC level is limited at the low end by the Level Control Circuits
and at the high end by maximum available power. Noise and
drift limit the range at the low end to -20
or greater. The
combination of RF frequency and RF components (different models
of synthesizer have different RF components) limit the ALC range
available at the high end. The internal instructions (firmware) of
the synthesizer limit the ALC level range available for request from
-20 to
If the power level requested is higher than the
synthesizer is capable of producing, the maximum available power is
produced, and the message line displays UNLVLED (unleveled). When
the synthesizer performs frequency sweeps at certain ALC levels,
maximum available power can be exceeded during small portions of
the sweep; in this case, a flashing UNLVLED message appears.
ALC leveling accuracy depends on power level. Although the ALC
level is from -20 to it is most accurate from
-10 to This fact is reflected in the performance
specifications of the synthesizer.
Coupled Operation. Since many applications require power output
less than -20 an optional step attenuator has a range of
0 to 90 in 10 steps. With this option, power output down
to -110 is achieved when the Step Attenuator and Level
Control Circuits work in conjunction (see Figure A-l). With the
attenuator, the ALC level is normally used over the smaller, more
accurate portion of its range. Since ALC level accuracy suffers below
-10
and at some frequencies only $1 of RF output is
available, the ALC level is set between -10 and 0 For power
less than -100 the attenuator is set to 90 and the ALC
level is used from -10 to -20 At frequencies where power
output above 0 is desired, the attenuator is set to 0 and the
ALC level is used from 0 to (or whatever power is available
at the RF frequency in use).
Coupled operation is assumed by the synthesizer unless
or Leveling Mode is selected. The proper
combination of ALC level’and attenuator setting is decided by the
firmware. In coupled operation, when desired power output is set via
Operating and Programming Reference HP 8360
User’s Handbook