Motorola Internal Use
14
V2288 – Circuit Description
See
Fig 4.1
for a block diagram of the transmitter stage to see how the 3 different bands
are created.
5)
The 38KHz PLL/VCO Stage needs to be phased because the amplified output is used
to demodulate the
HELP SIGNAL
into the original
L-R
signal. The 2
nd
output of the
amplifier is multiplied by 4 to get a 152KHz signal on
Pin 26
of the
U1001
.
•
This
152 kHz /MO_ST
signal output is used, while phasing, as a control signal for
the test set. The tolerance should be +/- 2KHz.
•
The
MO_ST
part of the signal works in conjunction with the
CLK_AM_FM
signal
to indicate the mono/stereo or tuned/not tuned status to the WhiteCap IC. (See table
below)
CLK_AM_FM
MO_ST
Result to WhiteCap PA5
LOW
LOW
stereo
LOW
HIGH
mono
HIGH
LOW
tuned
HIGH
HIGH
not tuned
6)
The
L-R
signal out of the mixer and the
L+R
signal from the 0-15KHz filter stage are
feeding into the Decoder Matrix. Result of sum and difference are the left
FM_L
and
FIG 4.1
L
R
L-R
MICROPHONE
STEREO
Modulator
Time and
Phase Correction
2f
f
19kHz
Pilot
kHz
U
0,03
5
10
15
2 0
25
30
35
40
45
19
38
5 0
55
L+R
L+R
L-R
L-R
Pilot
L+R
Help signal
Sum signal
Helpsingnal
38 kHz
