User's Manual

19/21
L21,C87 resonate serially and make impedance matching at receiver band-
pass filter.(FL1,FL2)
b) Front End
Front-end has Q6 to provide a high sensitivity and low noise feature.
It employs SAW filter as band pass filter to eliminate image frequency
and to produce enough pass band by Q6 input and output.
c) 1
st
Mixer
The receiver which has been amplifier in the RF front-end is provided to the
base of the 1
st
mixer Q7. The 1
st
L/O signal provide from the VCO is supplied
to the emitter of Q7 and Converted to the 1
st
IF 21.7 MHz
d) 1
st
IF Filter
The signal covered by Q7 to 21.7 MHz, the 1
st
frequency, change its
impedance through C48, and then is infused to the fundamental MCF which
has the center frequency of 21.7 MHz and the width of +/- 3.75 KHz.
Here, the signal reduces the image and other unwanted signal for the 2
nd
IF ,
and changes its impedance again through the R24. This filtered signal flows
in the 1
st
IF amplifier of RFIC(U2).
e) 2
nd
Mixer, and IF, FM Detect (U2)
The receiver IF signal of 21.7 MHz, which has been infused to U2 is mixed
with the 2
nd
L/O converted to 450 KHz, the 2
nd
IF frequency. The receiver
signal converted to the 2
nd
IF signal frequency passed through the FL3, the
ceramic filter of 450 kHz again.
The squelch circuit is composed to detect the noises from the received signal
demodulate in the 40
th
pin of the U2. For this purpose, the noise filter is using
the OP amplifier inside the U2
f) CTCSS Detector(U3, U4)
The 2
nd
IF frequency comes from No.26 pin of U2 and goes to MPU through
the active filter having U3 and U4.
g) Audio Amplifier(U10)
Demodulated audio signal enters to pin3 of AF IC (U10).
It comes out to pin5 then, it reaches at speaker.
5-3. Transmitt
When Tx develops with pressing PTT switch, VCO output amplifies through
Q3,Q2,Q1,Q12,Q16 transmits by antenna through low pass filter.
Tx RF signal produced from Tx VCO is amplified by Buffer Q3, Driver Q2
through C14, L11 and entered Q1,Q12,Q16 Power Transistor input
terminal with final amplification. After this stage, the signal is emitted at
antenna through 50

matching circuit to low pass filter (L3,L2,L1,C6,C5
C4,C3,C2,C1) to eliminate harmonic.
a) Audio Modulation and Audio Amplification
Audio signal produced by external or internal microphone, limits
amplification, low pass filter by IC U4.