HP 3336A - Page 31

Operation
3-10
NOTE
Use
discretion
when
using
the
Fast
Leveling
Mode
below
10
kHz.
At
frequencies
below
10
kHz,
the
Fast
Leveling
circuit
responds
to
the
instantaneous
amplitude
changes
of
the
output
signal,
resulting
in
distortion
and
degraded
amplitude
accuracy.
As
a
war-
ning
‘‘F.
bound
Err.’’
will
be
displayed
when
frequencies
below
10
kHz
are
entered
while
in
the
Fast
Leveling
Mode.
3-51.
Amplitude
Leveling
Mode
Selection.
To
change
from
one
leveling
mode
to
the
other,
SINGLE
press
the
BLUE
shift
key
followed
by
.
The
light
to
the
lower
left
of
this
key
will
be
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