Agilent Spectrum Analysis Basics - Agilent Technologies

Frequency stability: A general phrase that covers both short- and long-term
LO instability. The sweep ramp that tunes the LO also determines where a
signal should appear on the display. Any long term variation in LO frequency
(drift) with respect to the sweep ramp causes a signal to slowly shift its
horizontal position on the display. Shorter term LO instability can appear
as random FM or phase noise on an otherwise stable signal.
Full span: For most modern spectrum analyzers, full span means a frequency
span that covers the entire tuning range of the analyzer. These analyzers
include single band RF analyzers and microwave analyzers such as the ESA
and PSA Series that use a solid-state switch to switch between the low and
preselected ranges.
NOTE: On some earlier spectrum analyzers, full span referred to a sub-range.
For example, with the Agilent 8566B, a microwave spectrum analyzer that
used a mechanical switch to switch between the low and preselected ranges,
full span referred to either the low, non-preselected range or the high,
preselected range.
Gain compression: That signal level at the input mixer of a spectrum
analyzer at which the displayed amplitude of the signal is a specified number
of dB too low due just to mixer saturation. The signal level is generally
specified for 1 dB compression, and is usually between +3 and –10 dBm,
depending on the model of spectrum analyzer.
GSM: The global system for mobile communication is a widely used digital
standard for mobile communication. It is a TDMA-based system in which
multiple communication streams are interleaved in time, enabling them
to share a common frequency channel.
Harmonic distortion: Unwanted frequency components added to a signal
as the result of the nonlinear behavior of the device (e.g. mixer, amplifier)
through which the signal passes. These unwanted components are
harmonically related to the original signal.
Harmonic mixing: The utilization of the LO harmonics generated in a
mixer to extend the tuning range of a spectrum analyzer beyond the range
achievable using just the LO fundamental.
IF gain/IF attenuation: Adjusts the vertical position of signals on the
display without affecting the signal level at the input mixer. When changed,
the value of the reference level is changed accordingly.
IF feedthrough: A raising of the baseline trace on the display due to an
input signal at the intermediate frequency passing through the input mixer.
Generally, this is a potential problem only on non-preselected spectrum
analyzers. The entire trace is raised because the signal is always at the
IF, i.e. mixing with the LO is not required.
Image frequencies: Two or more real signals present at the spectrum
analyzer input that produce an IF response at the same LO frequency.
Because the mixing products all occur at the same LO and IF frequencies,
it is impossible to distinguish between them.
113