Amber 5500 - Page 8

PrOgrammable
Audio
Measurement
System
Section
2
A more
generalized
case
of the “track oscil-
lator” mode
can be enacted
by using Special
Function
37.
Whereas
Special
Function
6
concerns the
tuning
mode of
the notch filter
in the THD mode
only,
Special
Function
37
affects filter
tuning
in all
modes
(THD
and
Narrow band
level)
and also the
detector
integration
time constants and the
displayed
frequency
value. Each of
these under normal
conditions
is determined
by
the
frequency
of
the INPUT
signal.
That
is,
the
auto-tuning
of
the notch in THD
and the band
pass
filter in
Narrow
band,
the detector
integration
time
in all
modes and the
displayed
frequency
value in
all modes is determined
by
a meas-
urement of the
input signal. By
selecting
Special
Function
37.1,
all of these functions
are
instead slaved to the
internal
oscillator;
37.0 returns to the normal
default state.
37.1
is
useful to
gain
a
speed advantage
in
almost all
THD measurement
situations
(but
the
frequency
of the INPUT test
signal
must
be
close to that of the
5500
generator).
If the
input
signal
is
constantly being interrupted,
for
example
as
multiple
devices under test
are
sequenced,
this mode will
prevent
the
tuning
lock
interruption
as the
input signal
is
changed.
The filter
will remain tuned to
the
internal
oscillator
(and
the
FREQUENCY
dis-
play
will
continue to
give
the
oscillator fre-
quency)
even
when the
input signal
is
removed. When the
input
is
reconnected,
the
filter
nulling
will
proceed
faster as the filter is
already
tuned. To
select the
ngillator
tuning
mode,
set
Special
Function
37.1.
To
return to
the
normal
1mm;
tune
mode,
set
Special
Function
37.0.
Remember
that if
Special
Function
37.1 is
set,
the
input signal
must be
the same
frequency
as the
5500 source. If
not,
an erroneous
reading
will
result. Also
remember
that
this
mode
changes
the FRE-
Amber
model
5500
Owner’s
Manual Version
07
QUENCY
display
to be GENERATOR
FRE-
QUENCY
rather
than INPUT
FREQUENCY.
2.1.6 INTERMODULATION
DISTORTION
(IMD)
(Requires option
002)
This mode measures the
intermodulation
products generated
in a
device under test
when stimulated
by
an
appropriate
dual fre-
quency signal.
This is the
only
function of the
receiver section that
has an influence on the
generator
section. When this mode is
selected,
the
generator
changes
to a twin
tone
signal
from its normal
single
tone mode.
Two
types
of IMD are
measured
(and
generated).
The
primary
mode is SMPTE or
DIN
consisting
of a
high frequency
signal
and
a low
frequency signal
mixed in a 1:4
amplitude
ratio.
When the mode is
entered,
if the
generator
(HF)
frequency
is below
2
kHz,
it is set to
7
kHz
but
may
be later
changed
to
any high
frequency
between
2 kHz and
100
kHz. The low
frequency
is the
one most
previously
used but
may
be'
changed
to one of
eight
low
frequencies
between
401-12
and
500kHz
(see
Section
2.2.2).
Note that when
this function is first
selected after a default state
power-up,
the
low
frequency
is
at the default value of
60 Hz.
The
second IMD mode is CCIF
and is
selected
by using
the
shift
key.
This
mode
measures the low
frequency
difference com-
ponent
of a twin tone
high frequency
test
signal.
The difference
frequency may
be
any
frequency
from
80Hz
to
1 kHz while the
mean
frequency
of the dual
tone
high
fre-
quency may
lie between 2
kHz and
100
kHz.
As
in
THD+N,
the results
may
be
expressed
as a dB
ratio or
a
percentage.
2-6
fx