Fluke DDS Function Generator 271, User Manual

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Main Generator Operation
Main Generator Parameters
5
5-5
For example, in the display below, the p-p output is not attenuated by the fixed attenuator
and the actual dc offset (in brackets) is the same as that set.
FREQ=10.00000kHz
VhiZ=+2.50 Vpp 50
Ω
DC=+150.mV (+150.mV)
SYM=50.0% (50.0%)
If the output level is now reduced to 250 mV p-p, which introduces the attenuator, the
actual DC offset changes by the appropriate factor:
FREQ=10.00000kHz
VhiZ=+250.mVpp 50
Ω
DC=+150.mV (+15.1mV)
SYM=50.0% (50.0%)
The above display shows that the set DC offset is +150 mV but the actual offset is +15.1
mV. Note that the actual offset value also takes into account the true attenuation provided
by the fixed attenuator, using the values determined during the calibration procedure. In
the example displayed the output signal is 250 mV p-p exactly and takes account of the
small error in the 20 dB fixed attenuator; the offset is 15.1mV exactly, taking account of
the effect of the known attenuation (slightly less than the nominal 20 dB) on the set offset
of 150 mV.
Whenever the set dc offset is modified by a change in output level in this way a warning
message that this has happened will be displayed. Similarly, because the dc offset plus
signal peak is limited to ±10 V to avoid waveform clipping, a warning message will be
displayed. This is explained more fully in appendix D,
Warnings and Error Messages
.
DC Output
The dc offset control can be used to provide an adjustable dc output level if the waveform
is off; the recommended set-up is as follows:
Select
GATE
edit mode and set the
SOURCE
to
MAN/REMOTE
. Exit edit mode and
turn on
GATE
mode with the
GATE
key. Provided that
GATE
mode is not triggered,
the
MAIN OUT
will now remain at the level set by the dc offset control.
On the main menu set the output level to 1 V p-p; this ensures that the software does not
warn of clipping (output level too high) and that the output attenuator is not switched in
(which would also attenuate the dc offset). With the cursor in the
DC OFFSET
field the
MAIN OUT
can now be adjusted over the range ±10V (into an open circuit).
Symmetry
Pressing the
SYMMETRY
key moves the flashing edit cursor directly to the symmetry
numeric field on the bottom line of the display. This is the only field that can be edited;
the bracketed field on the right-hand side shows the actual symmetry which might differ
from that set if the set value is outside that permitted for the selected frequency and
waveform combination. The limits are given in chapter 1,
Introduction and
Specifications
.
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