Chapter 2 37
Instrument Functions: A - L
AMPLITUDE / Y Scale
Instrument Functions: A - L
2.1.5 Presel Center
Adjusts the centering of the preselector filter to optimize the amplitude accuracy at the
frequency of the active marker. If no marker is on when
Presel Center is pressed, the
analyzer turns on the currently selected marker and does a peak search. If a marker is
already on, it should be placed on the peak of interest before pressing
Presel Center.
Some models of the analyzer contain more than one preselector. The microwave
preselector is used for frequencies from 2.85/3.05 GHz (depending on frequency band) to
26.8 GHz. The millimeter preselector is used for frequencies from 26.5 GHz to the
maximum frequency of the analyzer (the millimeter preselector is only available in
analyzers with a frequency range greater than 26.5 GHz). To center both preselectors, the
user must set up and request a
Presel Center in a microwave band, then set up and request
a
Presel Center in a millimeter band. (See Presel Adjust for more details.).
The unpreselected high band Option 123 lets you bypass the microwave preselector. (See
Input/Output, Microwave Preselector) Option 123 is only available in instruments with a
single preselector (
≤26.5 GHz maximum frequency.) Therefore, when the mircowave
preselector is bypassed, there will be no internal preselector available at all. In this case,
the
Presel Center and Presel Adjust keys will be grayed out (unless you are using external
mixing with preselected external mixers.)
For proper preselector centering, you should make sure that:
• if the marker is off, the highest peak onscreen is valid for centering and is in the range
of an active preselector
or
• if the marker is on, that the signal at the marker is a peak which allows centering and
is in the range of an active preselector.
Other considerations or cautions include:
• If a marker is already on, the analyzer will attempt the centering at the current marker
position and no peak search will be performed. (This allows the user to center the
preselector for signals which are not the strongest on-screen signals.)
• The microwave preselector (3 to 26.5 GHz) can be turned off (bypassed.) See
Input/Output, Microwave Preselector. If it is off, this functionality is not available.
• If the signal at the marker position is unstable the algorithm will not function properly.
An example of this would be noise or a noise-like signal like a CDMA digital
communications signal.
• There is no preselector for signals below 3.05 GHz (in band 0).
• With Input Mixer (Ext) selected and the Mixer Type set to Presel (preselected), Presel
Center
adjusts the frequency of the external preselector filter to maximize the
amplitude at the active marker frequency.
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