4 - 5
4-5 OTHER CIRCUITS
4-5-1 COMPOUNDER CIRCUIT (MAIN UNIT)
IC-F50/F51 have compounder circuit which can improve S/N
ratio and become wide dynamic range to suppress the
transmitting signal and to extend receiving signal. The circuit
is composed of the base band IC (MAIN unit; IC10).
(1) IN CASE OF TRANSMITTING
The audio signals from the microphone are applied to the
base band IC (IC10, pin 3) via microphone mute circuit
(FRONT unit; IC406), microphone amplifier (IC407), etc.
The signals are amplified at the amplifier section, and are
then applied to the compressor circuit to compress the audio
signals. The signals pass through (or bypass) scrambler
section, and are then amplified at limiter amplifier section
after being passed through the high-pass filter. The ampli-
fied signals pass through the low-pass filter section, and are
then applied to the modulation circuit (Q13, D16–D18) via
the FM/PM switch (IC11), low-pass filter (IC5) and D/A con-
verter (IC6).
(2) IN CASE OF RECEIVING
The demodulated AF signals from the IF IC are applied to
the amplifier section of base band IC (IC10, pin 23), and
then pass through the low-pass and high-pass filter section
to suppress unwanted signals. The filtered signals pass
through (or bypass) scrambler section, and are then applied
to the expander circuit to expand AF signals. The signals
pass through (or bypass) scrambler IC (IC14), and are then
applied to the analog switch (IC13, pins 8, 11). The signals
are applied to the base band IC’s amplifier section (IC10,
pins 19, 20), and are then applied to the AF amplifier circuit.
4
5
6
7
11
12
13
14
LEDR
LEDT
LIGT
AFON
DUSE
MCON
CSFT
SPON
Outputs RX LED control signal.
Low: Lights ON.
Outputs TX LED control signal.
Low: Lights ON.
Outputs back light LED control signal.
Low: Back light is ON.
Outputs audio control signal.
Low: Outputs audio signals from
speaker.
• Outputs CTCSS/DTCS switching sig-
nal when transmitting.
High: Selected DTCS.
• Outputs Min. VR switching signal
when receiving.
Low: Select Min VR.
NOTE: Audio signals are prior to
transmitting.
Outputs microphone select signal.
High: While the internal microphone
is used.
Outputs shift signal for reference oscil-
lator’s frequency.
Outputs the internal speaker control
signal.
High: The internal speaker is select-
ed.
Pin Port
Description
number name
