Amber 5500 - Receiver Section

Amber model
5500
Owner’s Manual
Version
07
Programmable
Audio
Measurement
System
Section
2
2.1
RECEIVER SECTION
The RECEIVER section contains
a
level
measuring
function
(also
called
an
AC
voltmeter,
dB
meter,
noise
meter,
etc.)
and a
distortion meter
(also
called distortion
factor
meter
or,
incorrectly,
a distortion
analyzer).
As the level meter has a
high sensifivity
and
selectable
response weighting,
it
may
also be
used as a noise meter.
Most
operations
of the receiver
require
a
single key
stroke and are
independent
(one
function is not conditional on
another).
In
general, they
result from a desire of the
operator
to choose a mode of
operation,
modify
a
measurement or
change
a
method
of data
presentation
(as
opposed
to an inter-
nal
requirement
of
the instrument such as
“nulling”
or
“ranging”
as found
on earlier
manual
instruments).
2.1.1 IMPEDANCE
Impedance
is a
significant
factor in
several
areas of the
5500.
There are
eight major
parameters
that are concerned with im-
pedance.
Each of these can have an
effect on
measured
and/or
generated
values.
They
are:
a)
Generator Source
Impedance
-
This
is the
output impedance
of the
5500
generator,
that
is,
the drive
impedance
seen
by
the load
looking
back into the
generator.
See Section
2.2.5.
'
b)
Generator
Load
Impedance
-
This is usual-
ly
the
input impedance
of the extemal device
under test. While
its nominal
value
may
be
known,
only
an
actual
measurement can
determine the
precise
value.
(E.g.,
a device
may
have a nominal
600 ohm
input
im-
pedance
but the actual
impedance
may
be
603.7
ohms.)
‘
c)
Specified
Generator
Load
Impedance
-
This is the user
entered value
telling
the
5500
the actual device
under test
input
impedance
or the
5500
generator
external load. It is
entered on the
keyboard,
stored in non-
volatile
memory
and used
to
determine
gen-
erator
output
level.
(Note
there are
two
values
-
one for
dBm,
one for V
and
dBV.)
See Section
2.2.6.
d)
Generator
dBm Reference
Impedance
-
When the
generator
output
amplitude
is
specified
in
dBm,
the reference
impedance
used to calculate
the.
dBm
value is the
specified
load
impedance.
E.g.,
if the exter-
nal load
is
specified
as
600
ohms,
a
requested
output amplitude
of
0
dBm
will
produce
0.7746
V ms
in the extemal
600
ohm resis-
tor.
However,
if the external
load is
specified
as
150
ohms,
a
requested output
amplitude
of
0
dBm will
produce
0.3873
V
rrns into an
external
150 ohm load.
e)
Device
Under Test
Output Impedance
-
The
output
source
impedance
of
the device
under test
will form a
voltage
divider with
its
load,
usually
the
input impedance
of the
5500,
to
affect its
output
level.
E.g.,
a device
with a
600 ohm
output
impedance
and
producing
0 dBV into an
open
circuit will
produce
-0.052 dBV into a
100
k ohm
load,
2-3'