5
INSTRUCTIONS FOR MEASURING
THE
MOST
IMPORTANT PERFORMANCE
DATA
For
any of the
following measurements
all metal
shields must
be
installed on their
proper places
(
Shield on
rf-input
section, plus the large cover
plates
on top
and bottom
of the
tuner).
The
output voltage
of the
test
generator
is stated
in open
circuit voltage (o.c.v. ).
If
the
internal
(source)
Impedance
of
the test
generator
is
60
ohms,
then
the
voltage
developed
across the
tuners
60
ohm
input
will be
exactly
one
half
of
the
generators
o.c.v.
(see
iig.
4.2.-4).
Test generators which
are calibrated
to
indicate
the signal
voltage across the
nominal
terminating
impedance
have
to
to
be
set to one half of the prescribed
o.c.v. value.
The predominantly used test
frequency
of
94
MHz
is
to
be
taken as
a
guide only.
Prior to starting
any alignment pro-
cedures, \i should
be
checked
whether
or
not
that frequency
does not produce an interfe ence with a
neighbouring FM
transm tter. (This should
be
checked with
the test generator
connected to the tuner, but with
the
s
gnal turned
off
).
If
an FM
b
oadcast can
still
be received,
the
test frequency of
94
MHz
(or
87.5
MHz) should
be
altered
slightly.
For
all measurements:
Connect 15
kHz
low-pass
filter between tuner output
(
56,
channel I
or
channel
II
respectively) and
distortion analyzer
or audio-millivoltmeter.
5
.
1
.
Input
sensitivity
Test
equipment:
Test
generator,
frequency 94
MHz,
2
/iV o.c.v.,
modulated
with
stereo
modulator, 15 kHz
deviation,
modulating
fre-
quency 1 kHz ( L
=
R) pilot
carrier
9
%
(6.75
kHz deviation ).
Distortion analyzer
or
audio
millivoltmeter.
5.1.1.
Tuner:
Power switch depressed
Button STEREO
AUTOMATIC
( 47
)
depressed.
Adjust ge-
nerator
frequency until a
zero reading is obtained
on the
CENTRE TUNING
meter
(44)
(approx.
94
MHz).
5.1.2.
Calibrate distortion analyzer
(
or
audio
millivoltmeter
)
to
obtain
a
reference reading.
5.1.3.
Turn
off modulation to measure
signal to noise ratio.
The
tuners
sensitivity is within specifications when
obtaining a
ratio
of
30
dB
in the mono-mode.
(
The
input
signal
of
2
/xV
o.c.v. must not
trigger the auto-
matic
mono-stereo
changeover).
5.1.4.
Raise o.c.v.
level from the test generator to
20
juV
o.c.v.
and
measure
signal to noise ratio. The tuners
sensitivity \s
within
specifications
if
a
ratio of
30
dB
or more is
obtained
in
the
stereo-mode.
(
The
input signal of
20
mV
o.c.v.
must
be
sufficient to effect
positive triggering
of
the
automat-c
mono-
stereo
changeover
)
5. 2
.
Measuring
static
selectivity
See 4.6.6.
to 4.6.7.
19
To Next Page
Loading...
Need help?
General
