Circuit Description; Transmitter Circuits; Receiver Circuits - Icom FP-561 Service Manual

SECTION 3 CIRCUIT DESCRIPTION

3-1 TRANSMITTER CIRCUITS

3-1-1 TRANSMIT OUTPUT PULSE CONTROL
CIRCUIT
The 200 kHz/50 kHz pulse signals from the LOGIC unit via
J1 (pin 3) are passed through the buffer amplifier circuit (IC1,
pin 1 and pin 3), and are inverted and output from IC1 (pin 2
and pin 5) as 180˚ phase difference pulse signals.
The signals from the buffer amplifier are passed through the
integrate circuits (D1, R2, C3 and D2, R3, C4) which adjust
switching time for tuning ON Q6, Q7 separately to prevent
overlap of output pulses (200 kHz and 50 kHz). The integrate
circuits change the pulse signals which characteristics of 50
% duty-cycle to slow switching time for leading and leave
quick switching time for trailing.
The pulse signals are applied to the Schmitt NAND gates
(IC2, pins 1 and 5). Also trasmit triger signal from the LOGIC
unit is applied to IC2 (pins 2 and 6) via C86. Only when both
signals are input, IC2 outputs transmit signals from pin 11 or
pin 10.
3-1-2 TRANSMITTER OUTPUT CIRCUIT
The transmitter output circuit consists of the driver and out-
put circuits.
The driver circuit consists of Q2–Q5. The Darlington connec-
tion, used for switching circuits, consists of a pair of transis-
tors for Q2 and Q4, and for Q3 and Q5. This is because the
next circuit which consists of FETs requires quick switching
time for leading and trailing characteristics.
The output circuit consists of Q6, Q7 and T1. When no trans-
mission is occurring, transmit power is charged into C28 and
energy outputs at the next moment by turning ON Q6 or Q7.
3-1-3 OUTPUT POWER CIRCUIT
This circuit consists of IC10, Q11, Q12 and Q13. A signal
from the LOGIC unit controls voltage to be applied to the pri-
mary winding of T1 through these components.
• DIODE ISOLATION CIRCUIT
I
V
Fig.1
3-1-4 DIODE ISOLATION CIRCUIT
D3, D30, D4, D31, D9, D32, D35, D36 are symmetry-type sil-
licon-varister diodes. Interior connection is simulated as
shown in the diagram (Fig.1).
Fig.2 shows the diode's electronic characteristics. When the
voltage is +Vd or less, internal resistance is infinitie. This
condition is the same as when a diode is OFF. when the volt-
age exceeds +Vd, internal resistance for each diode is at its
minimum level. This condition is the same as when a diode
is turned ON.
When transmitting, high voltage is applied to the circuit and
when receiving, no voltage is applied. Therefore, the receiv-
er circuit is protected from high power transmit signals when
transmitting, and the receiver circuit is isolated from the
transmitter circuit when receiving.

3-2 RECEIVER CIRCUITS

3-2-1 RECEIVER MATCHING CIRCUIT
The matching circuits for the 200 kHz signal and for the 50
kHz signal consist of L1, C93 and L6, C96 respectively. The
tuned signals at each matching circuit are applied to the ana-
log switch (IC16).
The analog switch (IC6) switches received signals by the Rx
frequency control signal (LOCONT) from LOGIC unit via J5
(pin 5), and then outputs to the next stage which is the mixer
circuit.
When transmit/receive 200 kHz signal, LOCONT is low level
and pin 7 (IC16) is ON. Therefore, IC16 (pin 1) outputs tuned
200 kHz signal.
When transmit/receive 50 kHz signal, LOCONT is high level
and pin 6 (IC16) is ON. Therefore, IC16 (pin 1) outputs tuned
50 kHz signal.
–Vd
3 - 1
I
V
+Vd
Fig.2