Amber 5500 - Page 7

Amber model
5500
Owner’s Manual Version
07
characteristic with 12 dB
per
octave
roll-off.
Each of
these six
shapes
is selected one
at a
time,
as the
NARROW BAND
key
is
pushed
repeatedly.
The center
frequency
of the
band
pass
response
or comer
frequency
of the
high
or
low
pass
response may
be
specified
in
one of
two
possible
ways.
The default
condition is
for the filter
to follow the internal
oscillator.
Thus it is
automatically
set to the same
fre-
quency
as
the
generator every
time
a‘Source
Frequency
is
specified
(see
Section
2.2.1).
Alternatively,
the band
pass
filter
may
auto-
,matically
track the
input
in an auto-tune
mode. This
requires
first
that the
input
signal
be
-30
dBm/30
mV or
greater
and
second,
in
the
frequency range
10 Hz to
100
kHz.
The
instrument will then measure
the
input
fre-
quency
and
automatically
and
continuously
tune the filter to this
frequency.
To turn
on
the
auto-tune
mode,
select
Special
Func~
tion
28.2.
To
return to the normal
“follow
oscillator”
mode,
select
Special
Func-
tion
28.0.
2.1.5
TOTAL
HARMONIC
msrormorv
plus
NOISE
(THD+N)
This mode
measures the THD+N of
the
input
signal
by
the common
fundamental
rejection
method. That
is,
the fundamental of the
input
signal
is
eliminated
by
an automatic
rejection
circuit,
the
remaining
residual
signal
is
measured and its
amplitude
is
expressed
as
a
ratio of the
input signal
amplitude. Depend-
ing
on the nature of the
input
signal,
this
residual
may
be
predominantly
harmonics,
noise or some
combination of
each. Hence
Programmable
Audio
Measurement
System
Section 2
the
nomenclature Total
Harmonic
Distortion
plus
Noise.
The result of the
ratio
calculation
may
be
expressed
as
either a dB
figure
or a
percent-
age
figure
under
control of
the
shifted UNITS
key.
Note
that
the
fundamental
rejection
circuits
and ratiometric
measurement and
calcula-
tion circuits are all
totally
automatic in
opera-
tion.
Frequency
tuning,
ranging
and
nulling
are all
automatically
controlled
by
the
inter-
nal
computer
in
response
to the
input
signal.
The
instrument will
measure the
THD+N of
signals
with levels
between
-
30 dBm
(30 mV)
and
+40 dBm
(100 V)
and
fundamentals
between
10
Hz
and
100 kHz.
Signals
outside
this
range
will
generate
an error
condition.
(Error
20 or 21 and
Error
26
respectively)
If the
input signal
is
particularly noisy
and
unstable but
the test
signal
source
originates
from the
5500
generator,
it
might
be
desirable
to override the
automatic
tuning
to
inhibit
random
“hunting”.
An
example
of such
a
situation
might
be
SINAD
measurements
on
a
communications receiver
or
distortion
measurements
on a
loud
speaker
or
tape
recorder
with
poor signal-to-noise
ratio. It is
possible
to
suppress
the
auto-tuning
and
force the THD
notch
filter to
always
track or
follow the
internal
oscillator. In this
mode,
every
time a new
Generator Source
frequen-
cy
is
entered
(Section
2.2.1),
the THD
filter
will be set to
and held
at this
same
frequency.
To select
this
mode,
select
Special
Function
6.1. To return
to the
normal auto-
tune
mode,
select
Special
Function
6.0.
2-5