Swept Frequency Accuracy - HP 8340B Manual

4-4.
SWEPT FREQUENCY ACCURACY
Specification
Table 4-7. Swept Frequency Accuracy Specifications
Center Frequency/Sweep Width Mode (CF/AF)
Readout
Accuracy with respect to
sweep out voltage (sweep
time
>
100
milliseconds):
AF
^
n
x
5
MHz:
±
1% of indicated sweep width (AF)
±
time base accuracy*
AF
> n
x
5
MHz
to <
300 MHz:
±
2%
of indicated
sweep
width (AF)
AF
s
300 MHz:
±
1%
of indicated
sweep
width (AF), or
±
50 MHz, whichever
is
less
Where
n
=
harmonic multiplication number.
Refer to Frequency Ranges and Bandswitch Points
description
in
the specifications table
in Section
I.
* Time Base affects Center Frequency accuracy
only, not
Sweep
Width Accuracy.
Start/Stop Mode
Readout Accuracy with respect to
sweep out
voltage (sweep time
>
100
milliseconds):
Same as Center Frequency/Sweep
Width Mode.
Description
The HP 8340B/41B (DUT) RF
output
is
connected to the HP 8566B Spectrum Analyzer input. The
spectrum analyzer
is
set
for
zero Hz span at
a
CW frequency
within the
DUT swept
frequency range.
The spectrum analyzer VIDEO OUT (applied to the oscilloscope vertical input) will have
a
response
as
the
DUT
output passes through the frequency that the spectrum analyzer is tuned
to.
The selected
spectrum analyzer bandwidth filter will determine the shape of the response.
The HP 8340B/41B SWEEP OUT,
in series
with
a power
supply, is applied to an oscilloscope's
horizontal input. The input to
the oscilloscope
is
clamped at
±
0.7V by
two diodes to
prevent overdriv¬
ing the
oscilloscope's
input.
The oscilloscope is calibrated by setting the
DUT
and the spectrum
analyzer to
the same CW frequency (e.g., 20% of
Band).
To set the
DUT
to have
a
SWEEP OUT
voltage and at the same time
a
phase locked CW frequency that
is
proportional to
a
percentage
of
a
swept frequency band, the
START
and
STOP
frequencies are selected,
MANUAL SWEEP
is
selected,
and
a frequency equivalent
to the desired percentage of band is
selected (e.g.,
START
3
GHz,
STOP
5
GHz, MANUAL 3.4 GHz, for 20%). The power supply
is adjusted for
a
DVM
indication of
zero
volts and
the oscilloscope horizontal
position control
is used to position the dot to the center graticule
line.
With
the
oscilloscope horizontal
sensitivity set
to 0.05 V/Division, the
CRT
horizontal axis is now calibrated
to approximately 0.5% of the swept frequency range per
division.
The spectrum analyzer VIDEO
OUT
voltage to the oscilloscope
is
then maximum
and
the scope
vertical position
is
adjusted to place the
dot
near
the top of the
CRT.
The HP 8340B/41B
can
now be set to sweep
any
frequency range and the oscilloscope center
grati¬
cule line will
represent the calibrated percentage (e.g.,
20%)
of the sweep range. The
spectrum
analyzer center frequency is set
to
a
frequency that
is
the desired percentage (e.g., 20%) of the DUT
swept frequency range.
If
the
DUT swept frequency accuracy
is
perfect, the oscilloscope trace will be
the
response of
the spectrum analyzer's bandwidth
filter,
centered
on
the
CRT.
If
the trace
is
not
centered, the spectrum analyzer center frequency
is adjusted to position the response to the center of
the oscilloscope CRT. The amount
of
spectrum analyzer frequency change
is the
DUT Swept
Fre¬
quency Accuracy
error.
HP 8340B/41B
Performance Tests
4-21