TH-F6A/F7E4CIRCUIT DESCRIPTION1. A band receiver system1-1. Receiver circuitThe A band can receive signals in two bands: VHF (220 MHzband ) and UHF (K type: three bands). It usesFM receive mode only, and uses double conversion with thefirst IF of 59.85 MHz and the second IF of 450 kHz.The first amplifier is divided into two bands: 137 MHz -173.995 MHz (216 MHz - 260 MHz ) and 410 MHz- 470 MHz. The incoming signal from the antenna passesthrough a low-pass filter and a duplexer, and goes to anindependent amplifier (Q63, Q62) for each band.1-1-1. VHF band frontendThe incoming signal from the antenna passes through aVHF band low-pass filter and a duplexer, passes through aband-pass filter where it is tuned with varicaps (D76, D77),and goes to the first amplifier (Q63). Unwanted signalcomponents are eliminated by a two-pole band-pass filterwhere it is tuned by varicaps (D72, D75, D81, D83), and thesignal goes to the common mixer (Q45) for the A band. (Ktype only: For 200MHz band reception, D74 is turned off witha control signal to improve band-pass filter coupling andensure pass bandwidth.)ANTQ45MT6C04AEBPFAPC&VTUNEAMIXQ633SK320RFAMP BPFBPFMPUD76D77D72,D75D81,D83LPFLO1st IF59.85MHzFig.11-1-2. UHF band frontendThe incoming signal from the antenna passes through aUHF band low-pass filter and enters the first amplifier (Q62)common to both A and B bands. The amplified signal isdistributed by L distributors (L95, L96) and goes to the LC filtermodule (L92). Unwanted signal components are eliminatedby the filter, and the resulting signal passes through anotherband-pass filter and enters the mixer (Q45).ANTBPFQ623SK320RFAMPL95L96HPFLPFL92Q45MT6C04AEMIXLO1st IF59.85MHzBPFLC FILTERMODULE1-1-3. Circuits following IFThe signal heterodowned to the first IF of 59.85 MHz by themixer (Q45) passes through a 15kHz MCF (XF2) and unwantedsignal components are eliminated. The resulting signal isamplified by the IF amplifier (Q43) and goes to the FM IC (IC7).The FM IC heterodowns it to the second IF of 450 kHz. Then,the signal passes through a 15kHz external ceramic filter (CF4)and goes to the FM IC again. The signal amplified by the IFamplifier built into the IC is demodulated by the quadratureFM demodulation circuit using a discriminator (CD1) andconverted into an audio signal and output.The FM modulation signal output from the FM IC passesthrough a low-pass filter consisting of a resistor and a capacitorand is output to the control section. The demodulation signalinput to the control section goes to the electronic volume(IC706, pin 13) to adjust the audio balance with the B band.The output signal is amplified by the operational amplifier(IC717), passes through an active filter consisting of Q719 andQ717, and goes to the audio amplifier (IC707). The signalamplified to a higher power by the audio amplifier becomesthe final output signal from the set and output through theinternal speaker or speaker output pin (J701).Q45MT6C04AEMIXLO X3IC7XF2X1TCXOQ442SC4915IFAMPMCFQ432SC5108(Y)19.8MHZ CF44.50KHzLPFIC700VRBAFIC707Q719Q717AUDIOAMPDE EMPHASISIC717AMPSPJ701Fig.3Fig.21-2. Mixer local oscillator1-2-1. First mixerThe local oscillator signal for the first mixer is supplied fromthe VCO-PLL circuit.1-2-2. Second mixerThe local oscillator signal for the second mixer is a 59.4MHz signal that is produced by multiplying the 19.8MHz TCXO(X1) oscillator output with a multiplier (Q44).2. B band receiver system2-1. Receiver circuitThe B band has a broadband receiver circuit configurationand implements broadband reception of 100 kHz to 1.3 GHz.FM/AM/SSB/CW reception is possible in the range 100 kHz to29.7 MHz, and FM/wide FM/AM/SSB/CW reception is possiblein the range 29.7 MHz to 1.3 GHz. The FM/AM receiver circuituses double conversion with the first IF of 57.6 MHz and thesecond IF of 450 kHz. The SSB/CW receiver circuit uses tripleconversion with the first IF of 57.6 MHz and the second IF of450 kHz. The wide FM receiver circuit uses single conversionwith the IF of 10.8 MHz.
