HP 8360 B Series, Руководство пользователя

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Pulse Modulation
deviation
is
no longer limited by the FM rate, only by the maximum
limit of 8 MHz.
Pulse Modulation Pulse modulation can be accepted from an external source at the
PULSE connector or can be internally generated. The damage levels
of the PULSE input are
and -5 V DC. The input impedance is
50 A function generator must be capable of driving TTL levels
into a 50 load. With no input signal, the pulse input is held low,
so activating pulse with no input causes RF output to shut off.
The swept signal generator can also produce a 27.778 square
wave for use in HP scalar network analyzers. Swept signal generators
with Option 002 internally generate a synthesized pulse. The swept
signal generator provides internal pulse modulation with pulse widths
adjustable with 1
resolution (adjustable with 25 ns resolution with
Option 002).
Leveling
Pulse leveling performance depends on the accuracy of the diode
detector which measures the RF amplitude. The ALC block diagram,
Figure M-4, shows the pulse modulation input signal to the swept
signal generator which controls a pulse modulator. The pulse input
is represented by trace 1 in Figure M-5. The pulse modulator is
either full on or full off. The amplitude, when the pulsed RF is on,
is controlled by the linear modulator used for CW leveling and AM.
Trace 2 is the resultant RF pulse, which is the RF output. This pulse
is detected by the diode detector. It trails the pulse input because of
propagation delays in the pulse modulator and its drive circuits.
The output of the detector is amplified by a logarithmic amplifier
Trace 3 is the output of the log amp. Note that this signal is
delayed from the RF output signal and that the rise time is slower.
This is a result of the bandwidth of the detector and the log amp.
The amplitude of trace 3 is summed with the reference signal
from the level DAC and the difference (error) signal drives an
integrate-and-hold circuit. The integrator output drives the RF
output power level via the linear modulator. When the sum of the
detected and reference signals is 0 volts, the output of the integrator
is held at a constant level and the RF output is leveled.
Trace 4 is the delayed signal from the pulse input which controls the
switch in the integrate-and-hold circuit. Trace 4 is timed to coincide
with trace 3. Since the integrate-and-hold switch is closed only when
trace 3 is high, the integrator responds to correct the power level
only when the RF power is on.
Operating and Programming Reference M-19