
271
Users Manual
9-2
Introduction
FSK (Frequency Shift Keying) mode permits fast phase-continuous switching between
two frequencies. All other parameters of the waveform (amplitude, offset, symmetry) are
unchanged as the frequency is switched. For switching between waveforms where all
parameters can change, refer to chapter 11,
Hop
.
FSK can be controlled by the internal trigger generator, by an external trigger input, by
the front panel
MAN/SYNC
key or by remote control.
FSK mode is turned on and off with alternate presses of the
FSK
key; the lamp beside
the key lights when FSK mode is on. The FSK mode parameters (frequencies, trigger
source and internal trigger generator) are all set from the FSK edit menu which is
selected by pressing the
EDIT
key followed by the
FSK
key. When FSK edit is selected
the lamp beside the
FSK
key flashes to show edit mode regardless of whether FSK mode
is currently selected to be on or off.
FREQ A=10.00000kHz
FREQ B=10.00000MHz
SOURCE=EXT
TGEN=1.00ms 1.000kHz
Frequency Setting
The two frequencies,
FREQ A
and
FREQ B
, between which the waveform is
switched, are set in exactly the same way as the frequency on the main menu; in fact,
FREQ A is the main generator frequency in non-FSK mode and changing FREQ A on the
FSK edit menu will also change the frequency shown on the main menu.
Trigger Source
With the edit cursor in the
SOURCE
field of the FSK edit menu, the
DIGIT
keys or
rotary control can be used to select
EXT
ernal,
MAN/REMOTE
, or
TGEN
(internal
Trigger GENerator) as the trigger source which controls the frequency shifting.
With the source set to
EXT
ernal the frequency is switched at each rising edge of the
signal applied to the
EXT TRIG
input. The minimum pulse width that can be used with
the
EXT TRIG
input is 50 ns and the maximum repetition rate is 1 MHz.
With the source set to
MAN/REMOTE
, the frequency is switched with each press of the
front panel
MAN/SYNC
key or by the appropriate command via the RS232 or GPIB
interfaces.
With the source set to
TGEN
, the frequency is switched at each rising edge of the internal
trigger generator; the trigger generator produces a square wave with a period that can be
set from 0.02 ms (50 kHz) and 200 s (0.005 Hz). Period entries that cannot be exactly set
are accepted and rounded up to the nearest available value, for example 0.109 ms is
rounded to 0.12 ms. The generator output is available as a TTL level signal at the rear
panel
TRIG/SWEEP OUT
socket.
Setting the frequency of the internal trigger generator is fully described in the
Trigger
source
section of chapter 7,
Triggered Burst and Gate
.
Because the internal trigger generator can be used by the trigger, gate, FSK and AM
functions, and can be set from their respective edit menus, an information field is
displayed in brackets beside
TGEN
when this is selected as the source. This field will
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