d)
Center all
controls except for
GAIN
(adjusted in step (a)),
LOWPASS
FILTER
TUNING
(2-20kHz; full clockwise), and
HIGHPASS FILTER
TUNING (20-200Hz;
full counterclockwise). Place all
IN/OUT
switches
IN.
e) Measure
the noise
at
the main output of the
674A.
With the
test setup as
described,
it should not exceed -78dBm and will
typically measure
-80dBm. If
only the
80kHz
filter
internal
to the analyzer is available, the noise will
measure
somewhat
higher.
5)
Filter Sweep Tests
a)
Set
the oscilloscope for an X/Y display.
b)
Connect the
sweep generator output to
the
(+)
input of the
674A. Leave the
(-) input
connected to
circuit ground.
Connect the sweep generator
ramp
output to
the
"X"
input of the oscilloscope.
Verify that the
674A
main
output
is
still connected to the "Y" input of
the oscilloscope; if not, connect
it.
c)
Move
the EQ
IN/OUT
switch to
OUT.
d)
Move the
LOWPASS
FILTER IN/OUT
switch to
IN.
e) Adjust
the oscilloscope and sweep
generator to exhibit a
20-20,000Hz
logarithmically-swept response.
f) Adjust the
LOWPASS
FILTER
tuning control from
2kHz to 20kHz while
observing the swept response.
Verify that the
-3dB
points
correspond to the
panel
calibrations
+
1/3 octave.
Verify that the response
exhibits a
smooth
rolloff with a l2dB/octave
ultimate slope.
g)
Switch the
RANGE
to
200-2000Hz and repeat (f).
h)
Switch the
LOWPASS
FILTER OUT
.
Switch the
HIGHPASS FILTER
IN
.
i)
Repeat
step (f)
while sweeping the highpass
filter from
20-200Hz.
j)
Repeat step (f) while
sweeping the highpass filter from
200-2000Hz.
k) Switch the highpass and lowpass filters
OUT.
6)
Equalizer
Swept Response
The
following
procedure should be
performed on each of
the eight equalizer
bands in turn. As you perform
the tests, be
sure that the seven
EQ controls of
the
bands not under
test are
set
at
their center detents.
If the
OVERLOAD
lamp
flashes
at
any time, reduce
the
GAIN.
a)
Center
the TUNING and
BANDWIDTH
controls.
Adjust the
EQ control
throughout
its
range,
and verify
that
a
bell-shaped curve is produced.
The
peak gain should be adjustable
between
+
l6dB (6.31 times
the "flat" level) and
-l6dB
(0.158
times the "flat" level).
The response
should
be flat
+0.25dB when
the
EQ
control is set at its
center detent.
b) Set the
EQ
control at
+l6dB. Adjust the
BANDWIDTH control throughout
its
range. The peak gain
should change less
than 2dB
as
this is done.
c)
Adjust
the
BANDWIDTH control full counterclockwise
(full narrow).
Adjust
the
TUNING
control
throughout its range, and
verify that the
dial calibrations
are correct
+
1/3
octave. The curve should get
sharper
as
the
TUNING
control is
moved clockwise.
7)
Crosstalk
a)
Terminate the input
of the undriven
channel with
a
jumper
wire.
b)
Adjust all
EQ controls to their
center detents.
c)
Switch all filters
IN.
Switch both
LOWPASS FILTER
RANGE
switches to
2k-20kHz. Adjust both
HIGHPASS
FILTER RANGE switches
to
20-200Hz.
Adjust both
HIGHPASS
FILTER TUNING controls
to
20Hz,
and
both
LOWPASS
FILTER TUNING
controls to
20kHz.
d)
Adjust both
INPUT ATTEN
controls to
"7".
e)
Continue to sweep the channel under
test from
20-20kHz as in step
(6)
above. Adjust the
OUTPUT ATTEN of the sweep generator
to produce a
10V
p-p
output
as
observed on the
X/Y
scope.
19
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