Marconi Instruments 2955 - Page 38

OPERATION
0
DiSTN
ON-OFF key.
Causes
the
.Ai^
generator
to
generate
a
1 kHz tone
to
socket
{0.
The
display
indicates when
distortion
is selected.
Distortion
meter
operation
To make a
transmitter
distortion
measurement,
proceed
as
follows:-
(1)
Select
TX
Q.
TRANSNITITER TEST
is written
on the
screen.
(2)
Connect the
transmitter
output
to
the
RF IN/OUT
BNC connector
0
for
a
low
level
RF
output
or to
the RF IN/OUT N connector
(0
for a high
level
RF
output.
(3)
Press
SELECT
0
and
ensure
that
the LED
lights above
the socket selected.
(4)
The
instrument
automatically
tunes tathe transmitter’s frequency. If required,
the
transmitter
may
be tuned
for minimum or zero
indicated
offset using
the
2955
-
see
Transmitter
frequency
adjustment’.
(5)
Connect
the
AF
GEN
OUTPUT
socket
(0
to
the transminer’s microphone
input to
provide
amplitude,
frequency or phase modulation.
(6)
Press
DISTN
ON-OFF
©
until
DISTN is
displayed. This
causes a 1 kHz
tone to
be
generated
to
socket
0
to modulate the
transmitter.
(7)
Select
modulation
FM
0
,
AM
0
,
or 0M
0
.
(8)
Read the
%
distortion
from
the
display.
APPLICATIONS
Transmitter
frequency
adjustment
If
the
transmitter
setting, e.g.
400
MHz,
does not
agree
with the
measured
fre-
quency,
e.g.
400.000100
MHz, the
offset may be corrected
as
follows:-
(1)
With
TX
mode selected,
press FREQ and. then
enter
the
transminer
setting,
e.g.
400
MHz.
(2)
The
offset
is
displayed as a
positive
or
negative
value,
e.g.
tIOO
Hz.
(3)
Adjust
the
transmitter’s
internal
freque.ncy
while
observing
the
offset. Tune
until negative
values
are
seen and then readjust
positively
for zero
offset.
(4)
AUTO
TUNE
is
written
on
the
scr^s^n alongside
the
TX
key.
Press
this
key.
The 2955
automatically tunes
to
and displays the
transminer’s
corrected
frequency.
3-14
46881-622N
Apr.
88