User`s guide

7-86
Operating Concepts
Knowing the Instrument Modes
• The frequency of the incoming signal should be within −0.5 to +5.0 MHz of the selected
frequency or the analyzer will not be able to phase lock to it.
CW Frequency Range in External Source Mode 300 kHz to 3 GHz (6 GHz for Option
006)
Compatible Sweep Types The external source mode will only function in CW time
sweep. If the instrument is in any other sweep type when external source is activated, the
warning message CHANGED TO CW TIME MODE will appear on the display.
External Source Requirements The external source mode has spectral purity and
power input requirements, which are described in the 8753ES and the 8753ET
specifications and characteristics chapters of the reference guide.
Capture Range In either automatic or manual mode, you can enter the frequency of the
external CW signal using the softkey (located under the Stimulus key).
The actual signal must be within a certain frequency capture range as shown in Table 7-3.
If the incoming signal is not within the capture range, the analyzer will not phase lock
correctly.
Locking onto a signal with a frequency modulation component Although the
analyzer may phase-lock onto a signal that has FM, it may not accurately show the signal's
amplitude. The accuracy of such measurements depends greatly on the IF bandwidth you
choose. Use the widest IF bandwidth available (3 kHz) if this problem occurs.
Tuned Receiver Mode
In the tuned receiver mode, the analyzer's receiver operates independently of any signal
source. This mode is not phase-locked and functions in all sweep types. The analyzer tunes
the receiver to a synthesized CW input signal at a precisely specified frequency. All phase
lock routines are bypassed, increasing sweep speed significantly. The external source must
be synthesized, and must drive the analyzer's external frequency reference. The analyzer's
internal source frequency is not accurate, and the internal source should not be used in the
tuned receiver mode.
Using the analyzer's tuned receiver mode is useful for automated test applications where
an external synthesized source is available and applications where speed is important.
Although the tuned receiver mode can function in all sweep types, it is typically used in
CW applications.
Table 7-3 8753ET/ES External Source Capture Ranges
Mode CW Frequency Capture Range
Automatic ≤ 50 MHz
> 50 MHz
±5 MHz of nominal CW frequency
±10% of nominal CW frequency
Manual All −0.5 to +5 MHz of nominal CW frequency
CW FREQ
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