External Amplitude Modulation; Rf Power Control; Option 002 Step Attenuator; Alternate Sweep Mode With Option 002 - HP 83522A Service Notes

Operation
Model 83522A
sensitivity and coupling of the modulating
signal may be set via configuration switch
(A3S1). Figure 3-8 lists t h e a v a i l a b l e
configuration switch settings. The configuration
switch settings override 8350A Sweep Oscillator
non-volatile memory settings at Instrument
Preset.
3-26. External Amplitude Modulation
3-27. Pulse Modulation (PULSE I N Con-
nector on Plug-in). The PULSE IN connector
provides pulsed or square wave modulation,
where the RF output is switched on and off. This
input provides an onloff power ratio of greater
than 30 dB below specified maximum leveled
power. The PULSE IN input is normally at a
TTL HIGH (approximately +3 Volts dc). When
a TTL LOW signal (approximately 0 Volts dc) is
applied, the RF output is turned off. RF power
may be square wave modulated at repetition
rates up to 30 kHz at any power setting. The
input impedance for TTL level signals is
approximately 500 Ohms. If the PULSE IN
circuit is driven beyond TTL levels, the input
impedance is reduced to approximately 200
Ohms due to diode clamping action. See the
specifications and supplemental characteristics
in Section I for more details on the modulation
characteristics when using this input.
3-28. Amplitude Modulation (AM INPUT
Connector on 8350A). The AM INPUT
connector provides linear amplitude changes
(up to approximately 15 dB) proportional to the
modulating input voltage. It is limited to a
frequency response of about 100 kHz. For
maximum depth of modulation (i.e., maximum
modulation index), the RF power level should
be set to the middle of the control range (e.g.,
+5.5 dBm for a plug-in with calibrated power
control from -2 to +13 dBm). For plug-ins
equipped with Option 002 (70 dB Step Atten-
uator), the middle of the attenuator range should
be selected. The center of the power control
range may be selected with the front panel
power control knob or by applying a dc bias
voltage on the external modulating signal. A
positive (+) dc voltage into the AM INPUT
causes a decrease in RF output power; a
negative (-) dc voltage causes an increase in RF
output power.
3-29. RF Power Control
3-30. The RF power selected at power-up
(Instrument Preset) may be either maximum
power (4-13 dBm) or power OFF as chosen on
the configuration switch (A3S1); refer to Figure
3-8 for this setting. The configuration switch also
has switch settings for the model plug-in and use
of Option 002 Step Attenuator. The config-
uration switch settings override Sweep Oscil-
lator non-volatile memory settings at Instrument
Preset. Switch numbers 1, 2, 3, and 7 are set at
the factory and should not be changed.
3-31. Option 0 0 2 Step Attenuator
3-32. With Option 002 installed, when the
selected POWER setting goes below -2 dBm,
the step attenuator increments as required in
10 dB steps to a maximum attenuation of 70 dB
(which sets minimum power to -72 dBm).
Within the individual 10 dB steps of the
attenuator, the ALC loop adjusts the power
output to the power level programmed by the
front panel POWER control.
3-33. Alternate Sweep Mode With Option
0 0 2
3-34. If Option 002 attenuator is installed, and
alternate sweep mode is selected, a slow sweep
default condition of 1 secondlsweep may occur.
This default condition only occurs when the
POWER settings of the two alternate sweeps
require the attenuator to switch after each sweep.
The program prevents the attenuator from
switching faster than 1 second per attenuator
change to prevent damage to the attenuator coils
due to overheating.
3-35. Phase-Lock Operation
3-36. The 83522A RF plug-in RF Output (CW)
signal may be phase-locked using an external
phase-lock signal applied to the 8350A Sweep
Oscillator FM INPUT connector (rear panel).
The phase-lock function provides a means of
obtaining a very stable CW frequency by
transferring the frequency stability of the
reference oscillator to the source. If the CW
frequency starts to drift, the phase difference
between the CW frequency and the reference
frequency (reference oscillator) is detected,
producing a dc voltage. The dc voltage is a
correction signal which restores the CW fre-
quency to its previous point. Stability of the RF
Output CW frequency is determined by the
stability of the reference oscillator. The CW
filter should be turned off in phase lock
operation.