Kenwood TM-221A Service Manual page 4

TM-221A/E/ES
CIRCUIT DESCRIPTION
Transmitter system
@ General
in the transmitter system the desired frequency is pro-
duced directly by an oscillator. Frequency modulation is
obtained directly thru the use of a varactor diode.
@ Modulation circuit
Audio signals from the microphone are applied to a
three-stage operational amplifier which adds preemphasis,
performs amplification and limiting, and includes a splatter
filter to remove undesired high-frequency components.
After amplification by the operational amplifier, part of
the audio signal is applied to the microphone check circuit
used in the low-power mode.
In the FM modulation circuit, the frequency of the
VCO is directly modulated by a varactor diode.
RO?
(TM-221E)
VR?
% (TM-22tA/ES),
—
TX-RX UNIT
TO FINAL UNIT
@ Preamplifier stage circuit
The output from the VCO enters the linear amplifier,
which is capable of high-quality signal amplification
because it operates entirely in linear mode. APC, (Auto-
matic Power Control) is performed by controlling the
collector voltage of the 3 stage final preamplifier stage.
@ Power amplifier circuit
The drive signal is applied to the power module and
amplified to the required level. In the model TM-221A/
ES heat is dissipated efficiently by a large mechanically
strong heatsink.
@ APC and SWR protection circuits
Fig. 3 shows the basic ALC (Automatic Level Control)
and SWR (Standing Wave Ratio) protection circuits. The
SWR protection circuit incorporates a CM coupler that
detects any reflected power caused by mismatching of the
antenna. After detection and amplification, this circuit
acts to lower the output contro! voltage, which protects
the power module by reducing the gain. The automatic
power control (APC) circuit incorporates a diode that is
used to detect a portion of the output from the power
module. The detected signal is amplified and is then used
to control the power control voltage. The control voltage
is inversely proportional to the output, so a constant
output level is maintained.
ee ea all
FINAL UNIT
ee en ny ANT
LS 6 ANT
= GNO
o bas
o "Ts ek
° is)
R2 d eX gabice
OTPI
= v NU VRI
eat od LL] Z VR ey
J
C16
BRE t | | |
16 $e em me ne em
|
|
iQ
bees
. es rei creed
Fig. 3 APC and SWR protection circuits
Condition
Operating vo! tage
Specifications
M57747 M57726
Current consumption
5
Input power
Output power
2G7ZL= 502
ZG=ZL=502 | 0.4 (Vcc1¥12.5V)
55
Case temperature (operating)
Storage temperature
—30~+110 —30~ +110
—40~+110 —40~+110
Table 4 Power module M57747 (TM-221E), M57726 (TM-221A/ES)
absolute maximum ratings (Final unit Q1)
TM-221A/E/ES
CIRCUIT DESCRIPTION
PLL synthesizer
Fig. 4 is the PLL system block diagram. The trans-
mitter and receiver systems of the TM-221A/E/ES have
independent VCOs and PLLs, but share a common low-
pass filter.
The VCOs are configured as subunits. This construc-
tion minimizes outside influence and improves frequency
stability.
DATA
CLOCK
RESET (W,T only)
10 VCO(X58-3090-00)
Fig. 4 PLL system block diagram
10.24MHz (K,M)
12,8MHz (T,W) > 1 (5)
1/8 divider
2-modulus
prescaler
(1/128, 1/129)
VCO input
53
fREF divider
1/A divider
{7-bit binary)
1/N Programmable divider
Se {10-bit binary) z
Shift register (21-bit)
©
Data input
from Control unit
Fig.5 PLL IC ; M54959P block diagram
21 pulse counter
The reference frequency division ratios (four values)
and comparison frequency divison ratio are supplied to
the PLL IC (M54959P) as external serial data. An internal
dual-modulus (1/128 and 1/129) prescaler enables the
entire pulse-swallow PLL circuit to be implemented on
a single chip. (See Fig. 5.) The switching functions
(SW1 and SW2) of the PLL IC are used to switch between
the 8R (receive) and 8T (transmit) operating voltages
in the transmit and receive modes.
The switch controls are applied together with frequency
division ratio data from the Control unit.
RX 133.305~137,300MHz (K,M)
133,300~135,295MHz (T,W)
TX 144.000~147.995MHz (K,M)
144,000~145.995MHz (T,W)
To unlock control circuit
Divides 10,24MHz
by 2048 (KM)
Divides 12.8MHz
by 2048 or 2560
(TW)
Comparison | fg
frequency
ue
4
7 5V
detector
To LPF
Data latch (21-bit)
Latch signal
To8T To8R
control contro
circuit circuit