Table of Contents
Advertisement
CIRCUIT DESCRIPTION
1) [RX]
1. RX Method: Double Super Heterodyne Method
1st IF
:
FM 39.15 MHz
2nd IF
:
2. Front End
VHF
UHF
3. Mixer
4. IF
450
kHz
The signal input from antenna passes through the duplexer FL1 and low pass
filter, then it is amplified at RF amplifier Q17. The amplified signal is led to
band pass filter and band switch D19, then input to the mixer Q16.
The signal input from antenna passes through the duplexer FL1 and low pass
filter, then it is amplified at RF amplifier Q20. The amplified signal is led to
band pass filter and band switch D23, then input to the mixer Q16.
The input signal to the mixer Q16 and the 1st local signal are added or
subtracted at mixer Q16, and the crystal filter XF1 selects the signal of
39.15 MHz, then it is amplified at the 1st IF amplifier Q18 after the adja-
cent signal is eliminated.
The 1st local signal from VCO output is supplied to the base of mixer Q16
passing through the buffer amplifier Q15. The upper side band of the local
signal is used in VHF band and the lower side band of the local signal is
used in UHF band.
The signal amplified at the 1st IF amplifier Q18 is supplied to pin 24 of IC5 for
demodulation. Also the signal of 12.9 MHz from the reference buffer output of
IC 2 is multiplied by 3 at Q19, then it is led to pin 1 of IC5. 2 input signals are
mixed in the mixer circuit inside IC5 and converted into the 2nd IF signal of
450 kHz.
The 2nd IF signal output from pin 3 of IC5 is supplied to pin 7 of IC5 after the
adjacent signal is eliminated at the ceramic filter FL3 in WFM mode, or at the
ceramic filter FL2 in NFM mode. The input 2nd IF signal is demodulated at the
limiter amplifier and quadrature detection circuit inside IC, then output from
pin 12 of IC5 as an AF signal.
3
Advertisement
Table of Contents
