Operation Section 3
3-11
mode which can be programmed to sweep frequency or
level in logarithmic or linear increments.
3-36. Oscillator Output Description. The output
configuration of the Model 1121A can be selected for
single-ended or balanced/floating operation using the
FLOAT key. Special functions 75, 76, and 77 select the
respective 50 ohm, 150 ohm, and 600 ohm source output
impedance.
3-37. Source Frequency Display and Selection. To
select the Frequency function simply depress the FREQ
key. The key’s LED and the KYBD legend will be illumi-
nated and the SOURCE display window will contain the
current frequency setting. Once the function is selected a
new frequency may be entered using the DATA ENTRY
keypad. Display units can be selected by depressing
either the Hz or kHz keys.
3-38. Source Frequency Lock Mode Description.
The Model 1121A source oscillator achieves high
frequency accuracy and resolution through the use of a
frequency lock technique. The design of the Model
1121A enables internal measurement of the oscillator
frequency. During initialization after power is applied or
when the LCL/INIT key is depressed, the oscillator is
sequenced through its five frequency bands and specific
frequencies settings are verified for accuracy. Tuning
errors are stored by the control program in internal
memory as calibration factors. If the oscillator fails to
function on any of the frequency bands, an error (30-34)
will be displayed as an indication of a hardware fault
requiring service.
3-39. When a frequency setting is entered the oscillator is
coarse tuned to the setting by the control program.
Thereafter, the internal frequency of the oscillator is
measured and fine adjustments are made by the control
program to tune the oscillator to within tolerance. Special
function 16 disables the frequency lock mode to enable
faster frequency updates and sweep rates where the full
frequency accuracy of the oscillator is not required.
3-40. Source level Display and Selection. To select the
Level function simply depress the LEVEL key. The key’s
LED and the KYBD legend will be illuminated and the
LEVEL display window will contain the current level
setting. Once the function is selected a new level may be
entered using the DATA ENTRY keypad. The level
function allows display and selection of the open-circuit
output level. When a level is selected, the
programmable amplifier/attenuator is configured by the
microprocessor circuits to one of the ranges listed in
Table 3-6. Special function 18 disables the automatic
range selection and holds the range that is active at the
time the special function was enabled. When the
range-hold mode is active, new levels may be entered
from 0 V up to the maximum value for the selected range.
This mode provides the ability to set levels over a wide
dynamic range without the possible delay and transients
associated with range to range transitions. The LEVEL
function can be incremented or decremented by the value
in the LEVEL STEP function.
3-41. Amplitude Display Units. Amplitude values for the
LEVEL, START and STOP functions may be displayed in
linear units of mV or V or as a logarithmic value in units of
dBV or dBm. Display units can be selected by
depressing either the mV, V, or dB keys. Special
functions 80 through 86 select the logarithmic display
mode converts the linear voltage display (open-circuit) to
a logarithmic value relative to 1.000 V rms. When a dBm
mode is selected, the actual power into the load is
calculated and displayed based on the open-circuit level
and source and load impedance selections.
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