Section
Ill
and
Log B/4.
When
A or B
is selected, the
panel
meter
irdicates
the anlplitude of the correspotding
inpul signal in
dBV
(l
Vrrns=0dBV).
The overall mcasurement range for
the Log
A and [.og ts an]piitude
lunctions
is from
-
74 dBV
(0.1
nrV
rns)
to
+
16 dBV
(J0
V nns)
providing
a
total of
100
dB
in two voltage ranges.
The 3575A alnplitude
readings are
displayed with 0.1 dBV resolution
over
the
cntire Ineasurenrent
range. \\4ren
ll/A is selected, the 3575A
nleasures
the
relative
amplitude of
(differcnce
bctwecll) the
two ilput sigrlals in
dB. The disptav
range for relative
rneasurerrents is from
-
100
dB
to
+
100
dB with
0.1
dB
resoiutior. Relative
arnplitude
readings
are displayed with
respe[t lo
clunnel A which is the rcference channel. A
ncgative reading indicates that the
signal applied to charnel
B is
/orler
in amplitude tlun the
signal applied to channel
A. A
positive
reading
indicates that the signal applied to
channel B is
greater
i\ amplitude than the sigral
applied
to
channel A.
333. Phase
Presentation.
With the DISPLAY
switch in the
PHASE
position,
the
panel
rneter indicates the
phase
difference between the two input
signals in degrees. The
display range for
phase
measurenents
is
from
-
192 degrees
to
+
l9l
degrees
with
0.1 degree
resolution.
The
r
192
degree
limits
provide
a
t
ll
degree oyerrange
capability
which eliminates
alnbiguous
readings
in the
t
180 degree
region.
3-34. Phase Reference. The
3575A
phase
readings are
dirylayol
with
respect
to channel A which is the rclerence
r:hannel.
A
negative
pluse
reading
indicates that ts
lagsAi
x
positive
phase
reading
means
lhat
B leads
A.
3'35. With
the
PHASE
REFERENCII switch
in
the
+
A
position.
the
panel
meter indicates the actual
phase
difference between the two input signals.
With
the PIIASE
REFERENCE switch
in the
-
A
position,
channel
A
is
inverted and the
phase
reading
is offset by 180 degrees.
For
example, with
a
phase
difference
of
+60
degrees
(B
leads
A) apptied to the inputs and the PHASE REFtr,RllNCli
switch set
to the
+
A
position.
thc
pancl
metcr will indicate
+60
degrees. lf the PHASE
REFERENCE switch
is
changed to the
-
A
position.
ohannel
A
will be inverted and
the
panel
rneter
will
indicate
-
120
degrees.
3-36. Uccause of thc
1
ll degree
overrange capability, thc
3575A
never
gives
alnbiguous
phase
readings.
This
means
lhat
it
is
not necessary to change
the
phase
reference for
measurements in
the
t
180 degree
rggion.
fhe ability to
charge the
phase
refercnce
is strictly a convenience fcaturc
rvhich is uscful for
some measurernent applications. One
exarnple
of
this is where it is neccssary to
make a
continuous
phase
vs.
lrequency plot
over 360
degrees
of
range. Consider the case where two signals are initirlly in
phase
and as
lrequency
is varied 1he
phasc
diffcrence
increases
in a
positive
direction.
With
the
ph-ase
reference
set to
+
A, the
plot
starts out at
0
degrees
and
increases
with
frcquency
until the
phase
difference reaches
approxi-
mately
+
192
degrees.
At this time, the 35754 reading
automatically
jurnps
to
"
168 degrccs and again
goes
more
positivc
with frcquency.
'fhe
result is
a discontinuous
plot.
-l-6
Model
3 575A
By
initialy setting the
phase
reference
to
-
A, howcyer, a
continuous
plot
could be obtained.
The
plot
would
start
out
at
-
180
dcgrees
and
continue
in a
positiye
di.rection
through
+
192 degrees extending the continuous range
by
180 degrees.
3-37. Analog
0utputs.
3-38.
Two BNC connectors, labelcd
ANALOC OUTPUT I
and
ANALOG OUTPUT 2, are located on
the rear
panel
of
the instrument.
On
the
standard Model 3575A,
ANALOG
OUTPUT
2 is
not
used. The remaining
connector,
ANA-
LOG OUTPUT 1, is connected through
a I
kilotun
resistor
to the aDalog
(dc)
voltage
applied to the
panel
nleter.
Since
this voltage
is
not
affected by errors within the panel
meter.
it is
more accurate than the
panel
meter reading.
For tliis
reason,
the amplitude
and
phase
accuracy specificatiorls
listed
in
Table 1-l apply to the analog output
and do nor
rcflect
the
:t
3 count
panel
meter
tolerance. The
arulog
output
voltage is
delined in the accuracy
specifications as
l0 InV
per
degree
for phase
measuremelrts
and l0 mV
per
dB/dBV lor amplitude
measurements
(with
>2
Nlegohnl
load
resistance).
In the Amplitude Display mode,
the aiulog
output voltage
ranges
from
"
I Vdc
(
100 dB) to
+
I Vdc
(+
100 dB). ln the Phase Display mode
the
voltagc
ranges
from
-
l.9l Vdc
(-
192 degrees) to
r
l.9l Vdc
(+
l9l
dcgrees).
The analog output resistance
is I Kilohrn
and
short-circuit protection
is
provided.
To
obtain
an output of
l0mV
per
degree
or
l0mV
per
dB/dBV,
the load
resistance
connected
to the analog output must
be
2
Megohrn
or
greater.
Additional
loading
will not damage
the i|strunent or
degrade the
linearity
but it will reduce
the output voltage
by an amount
proportional
to tlte load
resistance.
3-39. Dual
Analog
Outputs
(Options
001 through
003).
-l-.10.
For instruntents
equipped with dual
panel
nreters.
ANALOC
OUTPUT
I is connected to ihc
left,hand
(facinc
the lront
panel)
panel
meter
(allrflitude)
and ANALOG
OUTI'LJT
I
is
connected to
thc righrhand
panel
meter
(plt.rse).
The anaiog output nrltagcs
correspond
with rhe
respeclive
panel
nleler readings
and can
be
used
fnr
sirnL taneous
amplitudc
and
phase plotting.
For
further
infbr rution
conccrning Options
001 00-1. refer to Para-
graph
3-6,1.
3,41.
BASIC OPEBATING
PROCEDUHE.
3-42. lnstrument Turn
0n.
a.
Rcfer to Figure 3-5 and
perform
the
following:
l)
Remove
the
fuse
and set the line selector switch
to correspond with
thc
line voltage to be used
(l15
V or
230 V).
2) Replace
the fuse
using a 0.64, 250
V
slo-blo
for
l15 V operation or a 0.3A,
250
V slo-blo for
230V
operation.
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