The Sweep Facility 1250 Frequency Response Analyzer
6-2 CHFR/1250/2
6.1 INTRODUCTION
The setting up of single frequencies has already been described in the Generator Menu
Section. However, the 1250 can also carry out an automatic sweep from one
preselected frequency to another. This can be performed in either direction, using
logarithmic or linear increments.
The sweep can be selected to cover the entire frequency range from 10 µHz to
65.5 kHz, or any part of it.
A special form of Harmonic Sweep can also be performed, as described separately.
6.2 LOGARITHMIC SWEEP
The 1250 offers four ways of setting a logarithmic sweep, selected by soft keys. In each
case, the successive steps in Generator frequency are related by constant ratios,
defined as follows.
1. By n steps per decade. The ratio is the nth root of 10. Hence the frequencies appear
spaced at equal intervals if plotted along a logarithmic base line. See example, Fig.
6.1.
Figure 6.1 - Example of Logarithmic Sweep at 4 Steps per Decade
2. By n steps per octave. The ratio is the nth root of 2.
3. By n steps in the whole sweep. The ratio of ƒ
MAX
to ƒ
MIN
is calculated, let this be R.
The step ratio is then the nth root of R.
4. By the ratio of the new frequency to the previous one. Here the user can enter the
actual ratio required as a number, e.g. if each frequency is to be √2 times the
previous one, enter 1.414 under ratio.
6.3 LINEAR SWEEP
There are two ways of setting a linear sweep:
1. By n Hz per step, where the Generator frequency is altered by a constant number of
Hz per step throughout the sweep.
2. By n steps in the whole sweep. Here ƒ
MIN
is subtracted from ƒ
MAX,
the difference is
divided by n, and the result added to, or subtracted from, the previous frequency for
each step.
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