Operating instructions

OPERATING MANUAL 2945A
46882-311D 3-53
The level of RF signal present at the active RF input connector is measured at regular points
along the sweep and plotted progressively across the display, thus building up a graph of RF level
against frequency.
The uses to which this facility can be put are varied. Within the radio communication field these
can include examining the output of a transmitter for spurious radiations, for sideband response
or noise levels.
The activity of nearby transmitters can be monitored as an aid to locating interference.
Using the tracking generator facility, the frequency response of filters can be checked and their
pass bands plotted.
Setting up
Sweep range
The sweep range can be defined in two ways: either as a centre frequency and a frequency span,
or as a start frequency and a stop frequency.
The sweep range will depend on the signal or signals being examined and the harmonics and
other spurious frequencies that are to be located.
The datum points are defined using the data input keys in the same manner as other frequency
entries such as RF generator frequency or Tx frequency.
The datum point being defined is selected by pressing the relevant soft key, which will cause the
datum to be highlighted under the spectrum analyzer graticule on the display. The corresponding
datum will also be displayed. Thus START FREQ and STOP FREQ will appear together and
SPAN and CENTRE FREQ will appear together.
Centre frequency
Pressing the [Centre Freq] key highlights the legend under the graticule and allows the
entry of any frequency within the spectrum analyzer RF range. This frequency will then be the
centre frequency on the graticule. If a figure is entered which would result in the lowest
frequency of the span becoming a negative value, the span is reduced so as to set the span start to
zero.
The variable control is active when the
legend is highlighted. It will not adjust the centre
frequency to a figure below half of the set span frequency range.
The FREQ [
] and FREQ [ ] keys can be used to change the centre frequency when the
legend is highlighted. Each press of one of these keys will increment the centre frequency by the
value last set up in the TxTEST mode.
Span
Pressing the [Span] key highlights the legend under the graticule and allows the entry of
any frequency within the spectrum analyzer RF range. This frequency will then be the frequency
range covered by the frequency sweep. If the frequency entered conflicts with the centre
frequency, by requiring a bottom frequency below zero or a upper frequency which is outside the
spectrum analyzer RF range, the span will be restricted.
The variable control is active when the
legend is highlighted.
The FREQ [
] and FREQ [ ] keys can be used to change the span setting when the legend
is highlighted.
Each press of one of these keys will increase or decrease the span setting to the next point in the
range 1 kHz, 2 kHz, 5 kHz,........200 MHz, 500 MHz, 1.0 GHz. The span setting is restricted by
the Centre Frequency setting, as explained above.