Model 8642A/B Operation
Amplitude (cont'd)
Depending on combinations of settings selected for amplitude and frequency and/or AM
that overrange specified amplitude levels, a message may occur indicating an automatic
leveling control (ALC) loop out-of-lock condition. However, the ALC loop out-of-lock
condition requires continuous microprocessor action that results in a slight increase in
noise, spurious signals, and Radio Frequency Interference (RFI). To eliminate these noise
levels,
either turn the ALC loop off (Special Function 4) or eliminate the overrange
condition. Refer to on page 3-197 for more information about these out-of-lock
messages,
Resolution is in dB When Setting Voltage Levels
Select voltage levels with a resolution as small as 0.001 uV (0.002 EMF uV). However,
internally the Signal Generator changes the output in units of dBm, with a maximum
resolution of 0.1 dB.
Converting Amplitude Units
Refer to Amplitude Units Conversion on page 3-205 for information about changing
amplitude values from one unit to another.
Time Required for Output Level Switching
Output level switching time is less than 100 ms from receipt of the last controller
command.
Units Used for Increment Set Can Be Different Than Units Used for the Amplitude
Setting
An amplitude increment value can be set using a different unit specifier than the unit
specifier displayed; for example, the amplitude increment could be in dB with an output
setting in volts.
When dBm, V, mV, uV, or dBuV is selected, the Signal Generator allows increment
settings in dB, V, mV, or uV.
When EMF V, EMF mV, EMF uV, or dB EMF uV is selected, the Signal Generator allows
increment settings in dB, EMF V, EMF mV, or EMF uV.
When the dBm and dBuV Keys Function as dBuV Terminators
Both the dB key ( f"GH7 UEffil ) and the dBuV key ( [ RAD % 1 ) function as dBuV
terminators when the amplitude is set in dBuV. All other relative amplitude settings use
only the dB key as a dB terminator.
HP-IB.
Either DB or DM
When selecting units in dBm, either HP-IB code DM or DB can be used. When selecting
units in dB relative, either HP-IB code DB or DM can be used. Therefore, amplitude
relative must be turned off (APRF) if you want DM to mean dBm.
HP-ID.
Sequence Dependency
Amplitude settings are sometimes coupled with Attenuator Range Hold (Special Function
9) or AM settings. Therefore, HP-IB codes may need to be entered in a particular
sequence when accessing combinations of these functions. Refer to the discussion about
Sequence Dependency which begins on page 3-12 in the HP-IB section of this Section III.
3-73
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