Circuit Description; Meter Circuit - Yamaha CT-7000 Service Manual

CIRCUIT DESCRIPTION

METER CIRCUIT

This circuit has two functions.
direct feeding of signals with strengths from
to 1 OOciB,u to the Signal meter. The other permits
selection of AM components in the FM signal, thus
showing the multipath element and displaying it as a
l4(80d8)J•I00d8)J) l!l50dBp-80dB)J) l2(30dB)I-50dB)J) II (10dB)J·30dB)J)
�r 0-1 g;l
Ul 06 N
N 08
....
0
Operation
1.
Signal Display
IF stage signals are detected at terminals
each is rectified to double voltage through the actions
of two diodes, then sent to Tr1. The signal strength
detection circuits are divided
For example, when a 1 OdB,u signal is received, the IF
stage amplifier connected to the
signal operating diodes 01 and 02 for the output.
a
That means that the 01, 02,
operating at this time. When a stronger signal is re­
h
ceived, input from rises above 10ciB,u to saturation
point (app. 30dB,u), at which time input is transferred
h
to to cover the 30dB,u-50dB,u range. The
is for
signals between 50ciB,u and BOdB,u, while
n
O
e permits almost
1
OdB,u
@;1
02
04
Q
I J ... I 4,
and
into· a series of four.
l1
terminal generates
C1, C , L1
2 circuit · i s not
I
terminal
3
14
Signal-minus-Multipath deflection. This system permits
the owner to find the best balance of strong and
"clean" signals by switching between the two functions
of this meter while experimenting with different antenna
locations.
TO MALTIPATH VERT. TERMINAL
covers the range from BOdB,u and 100dBJ.L This as­
sures excellent, linear meter response. These circuits
L1L2L3L4 (C1-C8)
-
are connected with
not AC.
2.
Multipath Display
The Signal meter display signal
to operate the meter. At the
element in the signal which shows multipath strength
is amplified and rectified to a half wave by 010. In
this way positive potential is obtained. At this
if the meter switch is set to S·M, positive potential is
(in
fed to Tr3 parallel with the si gnal meter) lowering
the impedance of Tr3 and reducing the Signal meter
amplification accordingly.
CT-7000
Fig. 1
OCcurrent,
is Tr1
amplified at
AC
same time, the
time,
5