Stanford Research Systems DS335, User Manual

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2-14 Sweeps & FSK
DS335 Synthesized Function Generator
Sweep/FSK RATE The duration of the sweep is set by [RATE], and the value is entered or
modified with the keypad. The sweep rate may be set over the range of
0.01 Hz to1 kHz. The sweep rate is the inverse of the sweep time, a 0.01 Hz
rate is equal to a 100s sweep time, and a1 kHz rate is equal to a 1 ms sweep
time. For a TRIANGLE sweep the sweep time is the total time to sweep up
and down. If FSK is selected from the UNI/BI menu, then the "Sweep Rate"
button sets the FSK Rate. If the rate is set to 0 Hz then the rear panel FSK
BNC input toggles between the two preset frequencies. For any non zero
rate the DS335 will toggle between the two preset frequencies at the
specified rate. The maximum internal FSK rate is 50 kHz.
Sweep/FSK FREQUENCIES The DS335 may sweep over any portion of its frequency range: 1
µ
Hz to
3.1 MHz for sine and square waves, 1
µ
Hz to 100 kHz for triangle and ramp
waves. The sweep span is limited to six decades for logarithmic sweeps.
The DS335's sweep range is set by entering the start and stop frequencies.
In FSK mode, the DS335 will toggle between any two frequencies: 1
µ
Hz to
3.1 MHz for sine and square waves, and 1
µ
Hz to 100 kHz for triangle and
ramp waves. There are no restrictions on the values of the start and stop
frequencies for linear sweeps.
Start and Stop Frequencies To enter the start and stop frequency press the [START FREQ] and [STOP
FREQ] keys. The span value is restricted to sweep frequencies greater than
zero and less than or equal to the maximum allowed frequency. If the stop
frequency is greater than the start frequency, the DS335 will sweep up. If the
start frequency is larger the DS335 will sweep down. If FSK is enabled the
DS335 toggles between the Start and Stop frequencies at the Sweep/FSK
Rate. If the rate has been set to zero then the rear panel FSK input is active.
A TTL low level activates the start frequency and a TTL high level activates
the stop frequency.
Sweep/FSK OUTPUT The rear-panel SWP/FSK output is synchronous with the sweep rate. This
output emits a TTL pulse at the beginning of every sweep cycle and can be
used to trigger an oscilloscope. When the start frequency is selected, the
Sweep output is at 0 Volts, and when the Stop frequency is selected the
Sweep level is at 5 Volts. The Sweep output is synchronous with the
frequency shifts.
FSK Input The FSK input accepts TTL level signals. When enabled (FSK mode with
0 Hz rate), it is sampled at a 10 MHz frequency by the DS335. A low TTL
level selects the start frequency, and a high TTL level selects the stop
frequency (see example below). When the FSK Input is being used, the
Sweep output is disabled and stays at 0 Volts.