Akai VS-2EGN

10.TV TUNER (FRONT END) FUNCTIONS AND CIRCUITS
10-1. TUNER FUNCTIONS
1) The signal from the antenna is received with mini-
mum loss.
2) Only required signals are selected and unwanted sig-
nals are removed.
3) The receiving channel is selected, and its band alone is
amplified. This is called RF amplification.
4) The frequency band is converted to an easy-to-
handle low frequency band. This low frequency (band)
is called an intermediate frequency (band). (IF). A fixed
10-2 CIRCUIT DESCRIPTION
The circuit will be described with reference to Fig. 7-113
(C). The VHF circuit will be mainly described, since the
VHF and UHF circuits are basically the same. The VHF
and UHF circuits differ greatly in that the VHF filter
uses a discrete component configuration, while the UHF
filter uses distributed component circuitry because of
the high frequencies at which it operates.
10-2-1 FILTER CIRCUIT
frequency is defined in each country.
The above are the main functions of the tuner.
Sub-functions are as follows:
@ The Automatic Gain Control (AGC) is provided to
control the RF amplifier gain to keep the IF output level
constant.
® The Automatic Fine Tuning (AFT) circuit is provid-
ed to keep constant the local oscillation frequency for
IF frequency conversion.
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Fig. 7-125 VHF band filter circuit
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IF FREQUENCY 100 200
In Fig. 7-125, LS1, LS2, and C1 constitute the LPF for
the UHF band. (In the UHF circuit, there is only an
HPF for the VHF band, with no LPF and no trap cir-
cuit.)
84
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300 400
FREQUENCY (MHz)—>
Fig. 7-126 VHF band filter characteristics
Lf2—5 and C5—9 constitute an HPF for cutting off fre-
quencies below the IF, and a trap is inserted at the IF
frequency.
Lf6—7 and C11—12 constitute an FM trap. Refer to
Fig. 7-126.
Service Manual VS-2EGN