a) Rx/Tx Conversion Circuit
Rx signal goes to Rx/Tx conversion circuit through FIXED antenna
connector, low pass filter(L5,L6,L7,C42,C43,C46,C47) and
receiver resonance circuit composed of L8,C1. When transmitting,
voltage through R25,L12,D6 supplies, D7 of receive input is short and
Tx is on condition. When PIN diode is off in condition of Rx, L8
and C1 resonate serially and make impedance matching at receiver
bandpass filter. (SF1).
b) Front End
Front-End has Q1 to provide a high sensitivity and low noise feature.
It employs SAW filter as band pass filter to eliminate image frequency
frequency and to produce enough pass band by Q1 input and output.
c) Mixer
Mixer has one base BFQ 67W(Q2) to feature high low noise quality.
It has RF signal through L7, L8, SF1,SF2 and Q1 RF signal from Local
oscillator mixed.
It develops 1'st IF ,21.7MHz. 1st IF goes to 1st IF amplifier Q3(KTC4080)
base through X-tal filter XF1.
IF of mixing signals is selected and enters the X-tal filter.
Output impedance of mixer is direct matched with input impedance
of X-tal filter.
Matching of filter satisfies pass bandwidth of filter, ripple
elimination within the pass band, and attenuation characteristic of stop
band. X-tal filter is composed of two pole monolithic X-tal filter,
with 8kHz of IF bandwidth. R11 is used as impedance matching with 1'st IF
Amp Q3.
d) IF AMP and Detection
1'st IF AMP Q3 supplies IF(U12) mixer input pin16 through output
resistor R13 and C21 to need gain in insertion loss of X-tal filter
and last stage circuit. Multi-use IF IC makes up of mixer IF AMP.
pin1 2'nd local frequency enter to pin 1.
It supplies mixer of internal IC. Mixer output of IC through pin3 passes
450kHz ceramic filter, supplies 2'nd IF amplifier and limits.
After 2'nd IF AMP has a process of enough gain and AM rejection,
it comes to quadrature detection. Demodulated audio signal by T1(Quad Coil)
is amplified and comes out to pin 9.
Detected audio signal through R22, VR1 and input in audio amp IC U4 through C22.
e) Squelch Circuit
Noise component of detected outputs has amplification
