HP 8753E Where AF’ is the spacing between frequency data points, Example, = 100 x lo-’ seconds

WINDOWMINIMUMNORMALMAXIMUM

LOW PASS ‘-J’-

IMPULSE

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Figure 6-72. The Effects of Windowing on the Time Domain Responses of a Short Circuit

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In the time domain, range is defined as the length in time that a measurement can be made without encountering a repetition of the response, called aliasing. A time domain response repeats at regular intervals because the frequency domain data is taken at discrete frequency points, rather than continuously over the frequency band.

Measurement range = -&

where AF’ is the spacing between frequency data points

(number of points - 1)

Measurement range = f r e q u e n c y span(Hz)

example:

Measurement = 201 points

1MHz to 2.001 GHz

Range = & or (number of points - 1) frequency span

(201- 1) = (10 xl 106) Or (2 x 109)

= 100 x lo-’ seconds

Electrical length = range x the speed of light (3 x l@m/s)

= (100 x lo-’ 6) x (3 x l$ m/s)

= 30 meters

In this example, the range is 100 ns, or 30 meters electrical length. To prevent the time domain responses from overlapping, the test device must be 30 meters or less in electrical length for a transmission measurement (15 meters for a reflection measurement). The analyzer limits the stop time to prevent the display of aliased responses.

6.136 Application and Operation Concepts