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SECTION 3
If the single-step
frequemy
increase/decrease
width
is
equated to the step width,
the step width can be repre-
sented as follows:
Step Width (Hz) = Sweep lvldth (Hz)
Number of steps
The MKR OUT signal is synchronous
with the sweep
steps. With an ascending sweep, the MKR OUT signal is
low when the sweep frequency is equal to or higher than
the marker frequency.
With a descending
sweep, the
marker output is high when the sweep frequency is lower
than the marker frequency.
The deviation
between the
set marker frequency
value and the actual transition
in
the MKR OUT signal is:
Marker Deviation
(Maximum):
i-Step width (Hz)
TheX DRIVE OUT signal will also change synchronously
as the sweep progresses. Because of the E-bit resolution,
the maximum
number of steps is 255, When the number
of sweep steps is less than or equal to 255, the number
sweep steps and the number of X DRIVE OUT steps are
the same.
Log sweep steps
The Model 3930A generates approximately
logarithmic
sweeps by overlaying
linear sweeps of about l/10 dec-
ade.
Number of steps per l/10 decade:
[Sweep
timdsed
x200/sweep
width(decade)]
or
[dLower limit frequency(Hz)
x 501, whichever
is smaller.
Number of sweep steps:
Number of steps per 1 /lO decade x sweep widthcdecade)
X10
Marker deviation:
zE?.5/number of steps per 1 /IO decade
(%I
In either sweep mode, the frequency at which the marker
output actudy
changes does not exceed the range be-
tween the specified
start frequency
and the stop fre
quency.
The
value
always
increases
or decreases
monotonically.
3.512
Output
Range Mode
Output Range Mode Description
Amplitude
control for both AC waveforms and DC offset
voltagesisperformedusingbothamultiplyingD/Acon-
verter and an output attenuator. When the output range
mode is set to AUTO, the output attenuator is controlled
by the amplitude
and DC offset values, and the output
voltage is determined
both by the multiplying
D/A con-
verter and the attenuator. Therefore, the waveform
am-
plitude
has 3-digit resolution
(VP-p and Vrms values)
and O.ldBV resolution
(dBV values), and the DC offset
also has 3-digit resolution.
Since an output attenuator
is
used, waveform quality (waveform
distortion,
precision,
and noise) remains high even when the output ampli-
tude is low. Amplitude
and DC offset are restricted to a
range that does not exceed 15V cumulative
voltage, but
when
the amplitude-to-offset
voltage
ratios become
large, the voltage with the smaller value becomes less
precise. Also, when the output attenuator
switches, the
waveform
output
is momentarily
turned
off, and the
both the waveform
and DC offset voltages are temporar-
ily interrupted.
When the output range mode is set to FXD (fixed), the
output
attenuator
is fixed at 0 dB, so that the output
changes virtually
instantaneously
without
interruption,
even if frequency, amplitude,
and DC offset are changed
(note, however, the output signal is momentarily
inter-
rupted for waveform and AM on/off changes). Also, am-
plitude and DC offset can be independently
set to values
not limited by a 15V cumulative
voltage value, and am-
plitude can be set to OVp-p. However,
amplitude
values
can only be set in Vp-p units, and they cannot be con-
verted to Vrms or dBV units. Also, only the A/D
con-
verter is used to set the amplitude,
so the smaller the set-
ting, the fewer the number of bits that are used for the
value. As a result, and the output waveform
quality is re-
duced. Also, although the amplitude
can be set to 0 Vp-p,
the actual output may differ somewhat from that value.
This deviation
from the ideal OV value tends to increase
as the output frequency increases.
Consequently,
the AUTO output range mode is most ef-
fective in situations where it is important
to have precise
output settings and good waveform
quality
down to a
low level, and in situations where output changes across
a wide range with similar offset and amplitude
levels are
required.TheFXDoutputrangemodeismost
effectivein
3-34
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