Philips Pm 5326 Bedienungsanleitung Seite 94

The AM modulator is represented by the
4
quadrant multiplier
IC
356
of unit
4.
When unmodulated the carrier is determined by a d.c. voltage
of input
4.
NF modulation is possible with amplitude of equal value as
this d.c. voltage; so 1 0 0 % modulation is possible. Potmeter
634
adjusts
the transmission characteristic to maximum
NF
suppression.
The 1 kHz oscillator,
IC
354
of unit
6
produces the sinewave signal
for internal modulation. External modulation is possible via buffer
stage 308.
Amplitude, automatic gain control
AGC
The RF signal signal at
IC
355.7
is rectified and amplified (transistors
306,
311)
and fed to the control input of
354.5.
Time constant
(649
+
644)/522
effects amplitude modulations of s 2 0 Hz not being gain controlled.
The amplitude is adjusted by potmeter
645.
The output amplifier is built up as impedance converter in cascode
stage 307, 308,resulting in maximum bandwidth. During retrace in the sweep
mode diode
406
closes transistor 308 cutting off the RF signal, see
Fig. 4.1-4.
r e f e r e n c e
o s c i l l a t o r s c a l e r
0,5
-
1,25MHz
0,l - 1,
2 5 MHz
+
phase c o m p a r a t o r
r a n g e
d.c. c o n t r o l
to RF output p c t h
I I
1
d i s p l a y
7 C 3
- 1 -
1 - 1
A C ~
n
-
1
T U M 0 2 0
u
:
-
d i v i d e r
-
Fig.
L. 1
-
1 ,
principle of operation
V C O
RF-oscillator
0,t - 1 2 5 MHz
c o u n t e r
U 2
I
\
,
LMHz X - t a l
o s c i l l a t o r
101
U 3
-
'
t i m e
b a s e
U
3