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SECTION 3
Operation
3.5.6
Output
Amplitude
and Amplitude
Modulation
Output
Amplitude
Pressing =D
displays the present amplitude
and en-
ables amplitude
programming.
When using numeric
keys to set the amplitude,
press the appropriate
units key
to complete the entry process (only p-p units can be speci-
fied in the fixed outputrange
mode). Press V or mV to en-
ter p-p units, use Vrms or mVrms for rms units, or press
dBV for dBV units. MODIFY
can also be used to change
an existing amplitude
value.
When the DC offset is OV, the allowed amplitude
range is
0.30mVp-p to 3O.OVp-p (AUTO output range mode) or
O.OOVp-p to 3O.OOVp-p (FXD range mode). If, however,
the programmed
DC offset is not OV, certain restrictions
concerning
the maximum
allowable
amplitude
apply,
and certain combinations
of amplitude
and offset values
may result in the "Er ACDC06 error". Paragraph 3.5.7 de-
scribes these restrictions
in more detail.
In the AUTO output range mode, the amplitude
can be
programmed
in rms or dBV units. Therms and dBV val-
ues are set on the assumption
that the average or center
level of the peak-to-peak
amplitude
of the waveform
is
OV. Thus, these values do not depend on the DC offset
value or square-wave
duty cycle.
The AMI'TD
key sets the amplitude
for AC waveforms
only; use the OFFSET key to set the DC output voltage of
the DC waveform
type. When the DC waveform
is se-
lected, you still can program
the amplitude,
but that
value can be entered only in p-p units (the allowed ampli-
tude ranges from 0.30mV p-p to 3O.OV p-p, AUTO output
range mode; O.OOV to 3OVp-p, FXD output range mode).
The specified value is stored, and it is used as the given
amplitude
for the next selected AC waveform.
Amplitude
Modulation
(AM)
Pressing the AM key allows
you to turn amplitude
modulation
on or off (l=ON,
O=OFF). You can use the
amplitude
modulation
function for all waveforms except
DC; however, amplitude
modulation
is intended primar-
ily for use with sine waves up to 1OOkHz in frequency.
When Ah4 is on, the selected AC output waveform
is am-
plitude
modulated
by an external signal applied to the
AM IN BNC jack. If the voltage of this modulating
signal
is Vm (in volts), the amplitude
of the modulated
output
waveform
is expressed as follows:
Output amplitude+p/rms)
=
0.5 x [Displayed
amplitude+p/rms):l
x (1 + Vm)
The range of Vm is -3V to +lV. When Vm = OV, the out-
put waveform
is unmodulated,
but the actual waveform
output amplitude
is one-half the displayed
amplitude.
When Vm < -lV, the output phase is inverted.
100% modulation
occurs when Vm = ilV
(2V p-p). If a
DC offset of -lV
is added to Vm, the carrier is sup-
pressed. If a DC offset of -2V is added to Vm, modulation
occurs with the phase of the output waveform
inverted.
3.5.7
DC Offset Programming
Pressing the OFFSET key displays the
current
DC offset
value and enables offset voltage programming.
When using the numeric keys to set the offset, press the V
or mV key after entering the value to complete the entry
process. As with
other parameters,
you can also use
MODIFY
to change an existing offset value.
With a DC waveform,
the programmed
offset voltage is
the DC voltage value that appears at the output jack.
Valid offset values are within the range of +15V to -15V.
For all AC waveforms, the DC offset is added to the aver-
age value of the peak-to-peak
amplitude
of the AC
waveform.
Certain restrictions
apply for amplitude-off-
set combinations,
and some combinations
of values may
cause an error (Er ACDC06) to occur. Even values that are
valid in a final combination
may cause errors when set-
ting up that combination.
See Table B-3 (Appendix
B) and
Figure 3-8 for relational range restrictions. To prevent er-
rors from occurring while programming
amplitude-off-
set combinations,
first set the offset to OV, change the am-
plitude,
then set the offset to the desired value. Use
Figure 3-8 as a guide when programming
offset and am-
plitude.
3-21
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