Operating instructions

LOCAL OPERATION
3-56
Overview
With the SPEC ANA mode selected, the screen and menu shown in fold out diagram (6-0) is
displayed.
In the SPEC ANA mode, the sweep generator causes the acceptance frequency of the analyzer
input circuits to repeatedly sweep over the selected frequency range.
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 center 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.
Center frequency
Pressing the [Centre Freq] key highlights the legend Centre under the graticule and allows the
entry of any frequency within the spectrum analyzer RF range. This frequency will then be the
center 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
Centre legend is highlighted. It will not adjust the center
frequency to a figure below half of the set span frequency range.
The FREQ [×] and FREQ [Ø] keys can be used to change the center frequency when the
Centre
legend is highlighted. Each press of one of these keys will increment the center frequency by the
value last set up in the TxTEST mode.
Span
Pressing the [Span] key highlights the legend Span 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 center
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
Span legend is highlighted.
The FREQ [×] and FREQ [Ø] keys can be used to change the span setting when the
Span 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.