Philips PM 5390 - Page 9

2-2
Output
attenuation
is
provided in two stages:
fine
adjustment
is
carried out by
the pin-diode
atteniito
r
in
the
RF
oscillator
unit,
providing
a
continuous
range from
0 to
20 dB in
1
dB
steps.
Coarse
attejH
^-
tion
is
achieved
outside
the
RF
box
by
a
100 dB
attenuator
in 10 dB steps.
For the
PM 5390
S
vefsion
a
20 dB
power amplifier
is added. The RF
signal is
then
fed
to the RF
OUTPUT
socket.
Frequency
modulation
signals are fed to
the
mixer
oscillator
VCO
3
in
order
to
have
a
constant
moclLi-
lation
coefficient. FM
is
only possible
in
the two
lower frequency ranges up
to 340
MHz, as
VCO^
is
active in
those ranges
only.
The
modulation
interface unit
3
processes
and
matches the
modulation
signals for the RF
units,
i«e.
the
Internal and
external FM, AM or VIDEO.
The
different modes are
controlled
via port 1 on
unit
1
.
The
sound
part
consists
of
a
sound carrier
oscillator/modulator
(switched in
during
VIDEO),
ajjilz
oscillator
and
an
input circuitry
for
external/internal
sound signals
for
generation of AM and FM
moclu-
lation.