HP 3575A Manual page 17

Model 1575A
d.
A.llow time
for
thc instrumert
to
stabil2e and
again
note the
low
level anrplitude reading.
e.
If
disconnecting the high
level signal ltas
produced
a
significant change
(1
0.5
dB)
in
the
bw
level reading,
a
ground
loop is
present and corrective
action
(Paragraph
3-l(r)
should bc taken.
3-19.
lnpul
Constrainls.
3-10.
The E0dB
dynamic range
of
the 3575A
provides
wide freedonr
lion)
input constraints. In
rnauy
cases.
it will
be
possible to
nral(c
all the
necessary
mcasurcments
without
changing voltage ranges.
It
is
irnportant. howcver.
to
obscrve
the
nr&\irnunr
input
levcls
(l
V rrns
or l0
V rms)
indjcated
b!
lhe Voltage
Range
settirlg.
Exceedilg
tliese
input
levels
rvill
causc
the
display
to
blank.
thc
overload
indicator
(AOL
or 861) to
illullliDatc
alld
car
datnage
thc
instrurllcnt
if
the applied voltage
is
greater than
l5
V rms or
50
V
dc.
3-21.
DC
lsolation.
3-::.
Thc -1575.\ inputs are
cquippcd
with
coupling
capacitors to pr()\'ide dc isolation.
The
maxinunr
dc
voltage
that
ca
be
:afeLy
applied Lo
the
inputs
is
i
50 Vdc.
Excceding
lhis lirnit
can
cause
breakdown
of
the
input
capacitors rL'sulting
in
ddnragc
to
the
ilput
arnplifier
circuitr!.
3-1.1.
fhc
-i575-{ ca
not
be operated
in
a floating
con-
ditioo.
All
IupLrt
ard
Output
conrmons
are
connected
dire.tl)
to outer
chassis
(iiame) gound
which
connects
to
earth ground rluough
the offset pin on
the powcr
cord
connector.
3-24. Voltaqe
Banges.
3-15.
E3ch
input channel
is
equipped
with
a range switch
which pennits
selzution
of two
overlapping
voltage
ranges.
lnput
voltage
Iirnits rvithin
each
ralge
are
as
follows:
0.1
rnv
rrns (-
74
dBV) to
I
V mrs (+ 6 dBV)
I
mV
rnrs
t
5.1
dBV)
to
l0
V
nns
(+
26 dIJV)
3-26. As
long
as
the
applied
sigul
is
within
the lirnits
ol
both
ranges
(2
mV to
I
V), either
range
settiirg can be used.
Changing
the
voltage range
settilB
does
not alfect
the
display resolution- For optimum
accuracy. however.
it
is
recomnrended
that the
0.:
nrV
to
I
V
ran8e
by used
at
all
tirnes uniess
the applied sigoai is greater than
I
V rms. The
reason
ior
this
is
that on
the
I
mV
1o
l0
V ralgc the input
signal is
divided
by the
l0
dB
inpul atteirullor.
Any
noise
tlut
is
gcnerxted
withir
the 15754.
however.
is
not
attenuated
and the sigrul
to
noisc
ratio is
decrcased.
Decreasing
thc sigml
lo
noise
ratio
rnakes
thc
instrunrertl
nrorc
suseptable
to
noise which can
affect tl)e
accuracy
of
amplitudc and
phase
rcadings.
It
should bc
noted that
the
Phase
Accuracy spocificrtions
(Tabie
l-l)
are nret
only'
when
the lowest applicable voltage range scttings arc
Llsed.
Section
III
3-27.
Frequency
Ranges.
-l-18. The broadband
frequencl
response
of
the
-]575A
extcnds
from
l
tlz to
13
MHz in four
overlapping
ranges.
frequency limjts within
each range are
as
foUows:
lHztolkHz
I
0 Hz
to
100 kHz
100
tlz to
I
Nltlz
I
kHz
to
13
IlHz
3-29.
The FRIQUENCY
RANGE
setting determines thc
amount
ol
filtering that
is
used
throughout
thc iustruntent.
The
filtering,
in
turn, controls the frequency
response and
overall settling
time
(See Tablc
3-l).
The frequcncy
ranges
are designed such
that the lower
limit ol
each range applies
to both
amplitude and phase
and the upper
lirnit
applics
or y to
phase.
For exarrplc,
it
is
possible
to
use
the
1
FL to
I kHz
rangc
for
al
anplitutlc mcasurcments
witllirl
the
liequency
range
of I
Hz
to
l3 NlfL. For
most arnplitudc
measuremcnts, however,
it
is best
to
use
one
of
the
upper
rarlges
k)
minimize settlin8
tiine. The main thing
to
remember
when making amplitudo
n)easurenlents
is
that
the frequency
of
the input
signal(s)
must be
above
the
lower limit
of
the
selected
frequency
range.
Vhen
mea-
s.rring phase.
it
is
necessary
to
observe
both the upper
and
Iower limits
of
each
freque|cy range. The
Lrppcr
linlits.
which apply
to
phase
only.
are
dctennined
by
noise
filters
which control the high frequency cutoff
characteristics
of
the phase detector circuits. For optimurn phase accuracy.
it
is nocessary
to
use
the frequency range
that
provides the
greatest noise immunity
ar./
the required
bandpass. This
means
that the
1r)i1'.,J1
range
Lhat covers
the frequency
of
the
input
signals
must be used.
It
should be Doted
that
the
Phase
Accuracy specifications (Table 1-l)
are
rnet
only
on
the Iowest applicable frequency range.
Table
3-1. Typical Settling Time.
(Iollowinq
a
change
in input parameters)
100%*
settled
95%*
Settl€d
90%"
Setrled
1
Hz'1
kHz
10
Hz-lO0
kHz
100 Hz
'l
MHz
l
kHz
. l3
MHz
30
sec.
3 sec.
0.3
sec.
30
ms
20
sec.
2 sec
0.2
sec.
20
ms
17 sec.
0.1
7
sec.
17 ms.
-
Percent
of
finrl
reading.
3-30. Meter lndication.
.l-31. nre
-1575A panel nleter
indicates
direotly
in
dB or
dBV
for
anlplitude
nreasurenrents
and
in
degrees
for
phase
rleasurenler)ls.
The
iront
panei DISPLAY
stvitch
penlits
sclcctiorl
of
cithcr
ANIPLITUt)E or PHASE
prcscltatiorr.
3-32. Amplitude Presentation.
With
thc
DISI'LAY sritch
ir,
tlre L\IPLlltLrl p,,.ili,,I.
IIrc
rr.lcr
l,re,er,rJIr'.. r'
deternrined
hy lhe
ANIPLITtiDI: FtINCTIO\
control
sctting.
-llle
tlrr.e irnplitude iilllctio
s
:rrc:
Log
A.
Log
B
Li