Stanford Research Systems DS335, User Manual

Page: 27 / 86

Sweeps & FSK 2-13
DS335 Synthesized Function Generator
FREQUENCY SWEEPS & FSK
Introduction The DS335 can perform frequency sweeps of the sine, square, triangle, and
ramp waveforms. The sweeps may be up or down in frequency, and may be
linear or logarithmic in nature. The frequency changes during the sweep are
phase continuous and the sweep rate may be set between 0.01 Hz and
1000Hz. The DS335 has a SWEEP output that may be used to trigger an
oscilloscope. The DS335 is also capable of Frequency-Shift Keying (FSK).
FSK can be implemented either through the internal rate generator or the
back panel external input to toggle between two preset frequencies.
Sweep/FSK Enable Sweeps are enabled by pressing [SHIFT][START FREQ] in the Frequency
Sweeps menu. The DS335 displays the "CONT SNGL" menu which allows
the user to choose between continuous and single sweeps. The DS335 will
immediately start a continuos sweep unless the user presses the UP/DOWN
arrow key to select SINGLE sweep. Once a single sweep is selected, the
[SHIFT][START FREQ] key triggers the sweep. If the user has selected the
FSK function from the "UNI/BI" (Unidirectional/Bidirectional/FSK) menu, the
single/continuous sweep option is disabled and the "FS OFF" menu appears,
giving the user the choice to enable or disable the FSK function. Once the
FSK function is selected and enabled, the FSK output signal appears at the
Function Out BNC.
Sweep Type Pressing the [SHIFT] [STOP FREQ] key sets the sweep to either a linear or
log mode. The UP/DOWN arrow toggles between the two sweep types. The
output frequency of a linear sweep changes linearly during the sweep time.
The output frequency in a logarithmic sweep changes exponentially during
the sweep time, spending equal time in each decade of frequency. For
example, in a sweep from 1 kHz to 100 kHz, the sweep will spend half the
time in the 1 kHz to 10 kHz range and half the time in the 10 kHz to 100 kHz
range). It should be noted that these are digital sweeps, and that the sweep
is actually composed of 1500 to 3000 discrete frequency points, depending
on the sweep rate.
Sweep Waveform The type of sweep waveform may be set to UNIdirectional (ramp) or
BIdirectional (triangle) by pressing the [SHIFT][SWEEP RATE] key and then
pressing the UP/DOWN arrow keys. If FSK is selected, Frequency-Shift
keying is enabled and the sweeps are disabled. If the waveform is UNI
(Ramp) the DS335 sweeps from the start to the stop frequency, returns to
the start frequency and repeats continuously. For BI directional sweeps the
DS335 sweeps from the start to the stop frequency, then sweeps from the
stop frequency to the start frequency, and repeats. If the DS335 is set for a
single sweep, the sweep occurs only once.