Kenwood TKR-740 Service Manual page 36

TKR-740
4.5 Receiver DDS circuit
The receiver DDS circuit varies the reference frequency of
the receiver main PLL to implement fine frequency steps which
cannot be achieved by a single-loop PLL. This circuit comprises
IC20, Q33, Q39, and CF5. The output frequency is used as
the reference frequency for the receiver main PLL.
Fig.18 Receiver DDS circuit
4.6 Baseband circuit
The baseband signal circuit consists of HPF Q26, LPF Q28,
D11, and Q29. The baseband signals detected by the narrow
FM and w ide FM detector circuits are de-emphasized by LPF
Q28. The sub-audible components of the signal are removed
by HPF Q26, and the resulting signal is switched with a squelch
signal by D11 and Q29, and output as an RA signal from CN6.
Fig.19 Baseband circuit
36
CIRCUIT DESCRIPTION
4.7 Other circuits
as in the transmitter circuit. Adjustment data for each unit
and the last channel data are w ritten into the EEPROM . IC2,
IC4, IC13, and IC16 are three-pin AVR ICs. Q17 is a ripple
filter for the pow er supplied to the first local oscillator VCO.
IC3 is a shift register. Q16, Q18, Q19, Q20, and Q22 are
sw itching transistors.
In addition, the receiver circuit contains an EEPROM (IC10)
Fig.20 Other circuits