Kenwood TH-F6A Service Manual page 7

3-6. Key/encoder input circuit
The PWR key is assigned to an interrupt port. The PTT key
is assigned to another interrupt port. The other keys and
destination diodes form a 5x6 matrix and pressing a key is
detected by scanning the matrix by software. The encoder
reads data through the interrupt port.
3-7. CTCSS/DCS
The encode signal is output from the D/A port of the CPU
(IC705) by software. The signal level is adjusted with an
electronic VR (IC706) and the signal is divided into VCO and
TCXO and modulated like a 9600bps packet signal.
The audio signal from the IF IC passes through the IC712/
IC711 waveform rectification circuit and enters the A/D port
of the CPU (IC705). The CPU detects that the specified CTCSS
tone frequency and DCS code are detected and controls
muting.
4. PLL • VCO
The TH-F6/TH-F7 has two PLL loops and a total of four VCOs,
two for each PLL loop. The PLL is divided for A band reception,
B band reception and transmission. Each VCO has oscillator
frequency shift control. For relationships between VCO
oscillator frequencies and shifts, see Table 4-11.
TH-F6A Frequency Construction
A band RX Double Super Heterodyne
RX Freq. Range
[MHz]
137.000
216.000
410.000
TH-F6A Frequency Construction
TX
CIRCUIT DESCRIPTION
2nd
Audio
2nd IF
Mixer
2nd LO
Fig.7
VCO Oscillation
[MHz]
173.995 196.850 233.845
259.995 275.850 319.845
469.995 350.150 410.145
Table.4
VCO Devider
Fig.8
Transmission
Band Frequency Range
[MHz] [MHz]
144 144.000 147.995
220 222.000 224.995
440 438.000 449.995
Table.5
3-8. DTMF
The DTMF signal is output from the D/A port of the CPU
(IC705) by software means. The signal is mixed with a signal
at the input side of the audio amplifier (IC707) and output as a
monitor tone. It is mixed with a modulation signal at the input
side of the preemphasis (IC701) and used to as a transmit
signal.
3-9. Serial control
The REM/PTT terminal of the speaker mic jack (J701) is
switched by the CPU (IC705) and functions as TXT/RXD to
communicate with a personal computer.
1st IF 1st Mixer Amplifier
VCO
1st IF 2nd LO 2nd
1st Mix. [MHz] [MHz] Mix.
Upper 59.85 59.4 Lower
Upper 59.85 59.4 Lower
Lower 59.85 59.4 Lower
Amplifier
VCO Oscillation
[MHz] Devide
576.000 591.980 4
444.000 449.990 2
438.000 449.995 1
TH-F6A/F7E
2nd IF
[kHz]
450
450
450
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