Filter
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I
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I
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sweep time
The time it takes the local oscillator to tune across the selected span.
Sweep time directly affects how long it takes to complete a measurement.
It does not include the dead time between the completion of one sweep
and the start of the next. It is usually a function of frequency span,
resolution bandwidth, and video bandwidth. Resolution affects sweep
time in that the IF filters are band-limited circuits requiring finite times to
charge and discharge. The amount of time the mixing product remains in
the IF
hlter
passband is directly proportional to the bandwidth; inversely
proportional to the sweep in Hz per unit of time. The rise time of a filter
is inversely proportional to its bandwidth, and if the proportionality
constant “k” is included, then we can make the rise time equal the “k”
divided by resolution bandwidth. Mathematically, this is represented as:
Time in
Passband
=
resolution bandwidth
(
reso u
aon
an
wz
1
t’
b d ‘dth x sweep time)
(span /sweep time)
=
span
Rise Time =
k
resolution bandwidth
Solving for sweep time:
sweep time =
k x span
resolution bandwidth2
time-gate
A time gate acts as a time
lilter,
rejecting signals and spectra not
corresponding to the desired time. It is an RF signal switch that admits
the signal to the analyzer only while the switch, or gate, is closed. Since
the analyzer receives the signal only when passed through the gate, it
will only display the measurement results from the portion of the signal
selected by the gate position in time.
title line
The area on a display where user-selected characters are displayed. These
characters are selected from the front-panel keys.
Glossary-26