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

 

(r e s o1 ut’aonb adn wz‘dth

x sweep time)

(span /sweep time) =

span

 

 

 

k

Rise Time =

resolution bandwidth

Solving for sweep time:

k x span

sweep time =

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