Stanford Research Systems DS345, Manual

Page: 32 / 139

Modulation and Sweeps
2-16
FREQUENCY MODULATION
Introduction
The DS345 is capable of frequency modulating any of its output functions,
except NOISE and ARB, using its internal modulation generator. The modu-
lation waveform may be a sine, square (FSK), triangle, ramp, or an arbitrary
pattern. The rear-panel MODULATION OUTPUT outputs a signal with 0V
corresponding to the smallest frequency output and +5V corresponding to
the largest frequency output.
Frequency Span
During FM the DS345 outputs a signal whose frequency range is centered
about the programmed frequency. SPAN sets the amount that the frequency
varies from the center frequency. The minimum frequency output will be the
center frequency - SPAN/2, while the maximum frequency will be the center
frequency + SPAN/2. The value SPAN/2 is commonly called the
deviation
(that is, SPAN = Deviation x 2). The SPAN is displayed and set by pressing
[SPAN]. The SPAN may be set with 1
µ
Hz resolution, and has a limited
range such that the output frequency is always greater than zero and less
than or equal to the maximum allowed for the function selected (30.2 MHz for
sine and square, 100 kHz for triangle and ramp).
Modulation Rate
Pressing [RATE] displays and sets the frequency of the modulating function.
The frequency may be set with two digits of resolution from 0.001 Hz to
10 kHz.