HP 3336A Operating Manual page 31

Operation
3-10
NOTE
SINGLE
on when the instrument is in the Fast Leveling Mode. Fast Leveling Amplitude Modulation
and Amplitude Blanking are mutually exclusive operating modes. That is, the instrument
cannot have Fast Leveling, Amplitude Modulation or Amplitude Blanking enabled at the
same time. For example, if the instrument is in the Fast Leveling Mode when Amplitude
Modulation is programmed, the instrument will automatically return to the Normal Level-
ing Mode. Conversely, Amplitude Modulation will be automatically turned OFF when Fast
Leveling is programmed.
3-52. Normal Amplitude Leveling and Amplitude Modulation. The Amplitude Leveling
circuit senses an increase in output power as the percentage of modulation increases because
of the presence of sideband energy. The Leveling circuit responds by reducing the signal
(carrier and sidebands) until the TOTAL output power equals the amplitude setting of the
instrument. This constant power regulation of the output causes what appears to be carrier
compression.
3-53. External AMplitude Leveling. An external Amplitude Leveling input (located on the
rear panel) allows regulation of the amplitude at a remote point. This input, marked EXT
LEVEL, has a nominal input impedance of 1 k ohm and a +1 V change at this input causes
a1 dB, + .25 dB change at the signal output.
A
Terminating or connecting the EXT LEVEL input to circuits other
than an active amplitude leveling voltage source will degrade the
amplitude accuracy. Leave this input disconnected unless external-
ly leveling the instrument.
3-54. Amplitude Blanking.
3-55. When the instrument is making a frequency change, the output signal does not instan-
taneously change to the new frequency. The potential exists in the Normal (no blanking)
operating mode, to produce unwanted energy at intermediate frequencies during a frequen-
cy change. In the Amplitude Blanking mode, the output level is automatically reduced dur-
ing the frequency change, resulting in the unwanted energy becoming insignificant.
Amplitude Blanking reduces the output level to less than — 85 dBm during the time the in-
strument is changing frequencies.
Model 3336A/B/C