Frequency Out Of Range; Frequency Out Of Range; Sweep Modes; Margin Below 0 Hz - HP 3580A Operating And Service Manual

Section III GENERAL OPERATING INFORMATION
Model 3580A
A -MODULATED
10 kHz SIGNAL
B- MODULATION
ENVELOPE
Figure 3-21. Amplitude vs. Time.
3-108. Frequency Out of Range.
3-109. There are a number of cases where the FRE-
QUENCY and FREQUENCY SP AN settings are such that
the frequency sweep attempts to go below 0 Hz or above
50 kHz. For example, if the start frequency is set to 10 kHz
and the FREQUENCY SPAN setting is 5 kHz/div (50 kHz),
the end frequency of the sweep is 60 kHz which is 10 kHz
above the 50 kHz limit. If the instrument is set for a center
frequency of 0 Hz, the start frequency is a negative value
and the area between the start frequency and the center
frequency is not meaningful.
3-110. To minimize erroneous indications, an internal
detector senses when the frequency sweep tries to go below
0 Hz or above 50 kHz and, in turn, clears the display. The
result is a clean baseline in areas where the frequency limits
are exceeded (Figure 3-22).
Figure 3-22. Frequency Out Of Range.
3-111. The frequency out-of-range detector is not exact.
Consequently, there are margin areas below 0 Hz and above
50 kHz where signals can be displayed. Typically, the
margin below 0 Hz is about 500 Hz wide. Signals displayed
in this negative margin are the images of the 0 Hz to 500 Hz
signals displayed on the positive side of 0 Hz (Figure 3-23).
The margin above 50 kHz is about 800 Hz wide and signals
up to 50.8 kHz can generally be displayed.
3-112. The frequency sweep will go out of range under any
of the following conditions:
a. When: Fstart
+
10 Fspan =
>
50 kHz
b. When: Fcenter
+
5 Fspan =
>
50 kHz
3-16
c. When: Fcenter - 5 Fspan =
<O
Hz
Where: Fstart =.start frequency of sweep
Fspan = FREQUENCY SP AN setting
Fcenter = center frequency of sweep
MARGIN
~
500 Hz
Figure 3-23. Margin Below 0 Hz.
3-113. Sweep Modes.
3-114. The front panel SWEEP MODE switch permits
selection of six sweep modes:
1) REP (Repetitive)
2) SING (Single)
3) RESET
4) MAN (Manual)
5) LOGZERO
6) LOG
3-115. Repetitive Mode. In the Repetitive sweep mode
the instrument sweeps continuously over the selected
frequency range. The duration of each sweep is determined
by the SWEEP TIME setting.
3-116. Single Mode. When the Single sweep mode is
selected, the instrument sweeps one time over the selected
frequency range and stops at the end frequency. The
instrument remains at the end frequency until another
sweep mode is selected or until a new sweep is initiated. A
new sweep can be initiated by:
a. Setting the SWEEP MODE switch to RESET and
back to SING.
b. Pressing the CLEAR WRITE button. This clears the
display and simultaneously resets the sweep. Do not use
clear-write when making x - y recordings.
c. External triggering as outlined in Paragraph 3-143.