Specifications

21
Some modern spectrum analyzers allow the user to select different LO
stabilization modes to optimize the phase noise for different measurement
conditions. For example, the PSA Series spectrum analyzers offer three
different modes:
• Optimize phase noise for frequency offsets < 50 kHz from the carrier
In this mode, the LO phase noise is optimized for the area close in to the
carrier at the expense of phase noise beyond 50 kHz offset.
• Optimize phase noise for frequency offsets > 50 kHz from the carrier
This mode optimizes phase noise for offsets above 50 kHz away from the
carrier, especially those from 70 kHz to 300 kHz. Closer offsets are
compromised and the throughput of measurements is reduced.
• Optimize LO for fast tuning
When this mode is selected, LO behavior compromises phase noise at
all offsets from the carrier below approximately 2 MHz. This minimizes
measurement time and allows the maximum measurement throughput
when changing the center frequency or span.
The PSA spectrum analyzer phase noise optimization can also be set to
auto mode, which automatically sets the instrument’s behavior to optimize
speed or dynamic range for various operating conditions. When the span is
≥ 10.5 MHz or the RBW is > 200 kHz, the PSA selects fast tuning mode. For
spans >141.4 kHz and RBWs > 9.1 kHz, the auto mode optimizes for offsets
> 50 kHz. For all other cases, the spectrum analyzer optimizes for offsets
< 50 kHz. These three modes are shown in Figure 2-12a.
The ESA spectrum analyzer uses a simpler optimization scheme than the
PSA, offering two user-selectable modes, optimize for best phase noise and
optimize LO for fast tuning, as well as an auto mode.
Figure 2-12a. Phase noise performance can be optimized for different
measurement conditions
Figure 2-12b. Shows more detail of the 50 kHz carrier offset region