Marconi Instruments 2955 - Page 49

CPEHATION
(?)
AC DC
key.
This
key
is
disabled
and
AC automatically
selected
whenever
DISTN
(^
or SIMAD
or
S/M
(^)
is
selected.
@
SINAD
S/N
key.
Selects
SIM.AD
or
signal/noise
and
causes
the
AP
eenerator
to
rhf»
signal
eenerator
”'ith
a I
V_Hz
tone.
"Te
crrxrAn
o-
S/N
is
selected.
*
'
’ --
--
Distortion
meter
operation
To
make
a
receiver
distortion
measurement,
proceed as follows:-
(1)
Select
RX
Q.
RECEIVER
TEST
is wrinen
on the screen.
p)
Set
the
signal
generator
to
the
frequency
of the
receiver
under
test
(see under
‘Signal
generator
operation').
(3)
Connect
the
receiver’s
aerial
Input
to
either the
BMC
socket
(T)
or the N
socket (i)
.
(4)
Connect
the
receiver’s
audio
output
to the
AF INPUT
socket
0.
(5)
If
required,
select
AP
GEM
(0
.
AUDIO TEST
is
written
on
the screen
and the
AF
generator
is
enabled.
See
‘Audio
test’
below.
(6)
Press
the
DISTN
ON/OFF
key
0
until
DISTN
is displayed.
AC coupling
and
the
0.3
to
3.4
kHz
band-pass
filter
are
automatically
selected.
(7)
Read
the
%
distonion
from
the
display.
If
required,
connect
an
external
psophometric
filter
to
the
ACCESSORY socket
(
0
.
Correct
connection
is
denoted
by the display showing
either CCii i or
C-
.MESS
in
place
of any
previously
selected
internal filter.
(9)
rress
the
SINAD
5/N
key
(0
unni SINAD
is dispiayed.
AC
coupling and
the
0.3 to
3.4
kHz
band-pass
filter are
automatically
selected,
(10)
Read
the
SINAD
in
dB from
the
display.
(11)
Press
the
SINAD
S/M
key
(0
until
S/N
is
displayed,
(12)
Read
the
S/N
in
dB from
the
display.
(13)
To
return
to
normal
operation,
select
DISTN OFF using key
©.
When
AUDIO
TEST
is
displayed.
AF
generator
operation
-
normally a
transmitter
function
-
is
enabled
in
addition
to the
receiver distonion
meter. This enables
the ge.nera-
tor
to
supply
the
signal
for
distortion
measurements,
e.c. to test
an
audio
amplifier
which
is connected
between
the
,AF
GEN
OUTPUT and
the
AF INPUT sockets.
Note
...
The
SINAD
S/N
key
(0
is
inoperable
during the
audio test.
46881
-622N
Apr.
83
3-25