Rf/If Section - Panasonic EURO 4 Chassis Technical Manual

12. RF / IF SECTION
The EURO 4 chassis includes an RF/IF combi tuner
which is located on the E PCB. The RF stage of the
combi tuner being characterised by:-
(1) A high input impedance.
(2) Low radiation from tuner.
(3) Low oscillator interference.
The tuner is designed for reception not only of the
conventional frequencies to date, bands I, III, IV and
V and the intermediate special channel frequencies,
but also for the 'hyper' band. This designation refers
to the frequency range from 300MHz to 470 MHz.
This frequency band is also of interest in view of the
growing number of cable networks and the
programmes which they offer.
A three band tuner is used for processing the large
frequency band from 47MHz to 681 MHz.
The extremely large tuning range in the bands
prohibits a band switch over with switching diodes
within the resonant circuits. Their switching capacity
in the VHF. band would:-
1. Excessively limit the tuning range.
2. Excessively limit the efficiency of the circuit
operation.
Because of the above drawbacks each band has its
own bias stage, correction circuits and band filter
with optimised tuning diodes. Each "part tuner" can
thus be biased and set for its frequency range.
The IF stage of the combi tuner contains the video
and audio demodulators which are designed for the
most widely used TV standards. For this reason the
stage is referred to as the multi-standard IF stage.
The IF stage for the EURO 4 chassis comes in 2
versions as follows:
1. LA7577
This IC201 contained in the IF stage is used to
process both video and sound IF frequencies.
This IC IC201
are not required to process the SECAM L
standard.
2. TDA9814
This IC201 contained in the IF stage is also used
to process both video and sound IF frequencies.
This IC IC201
which are required to process the SECAM L
standards.
Once the video and sound IF signals have been
processed, the video signal is fed to the VDP
and the audio signals to the MSP IC2101, all for
further processing.
25
3DQDVRQLF
LA7577 is used on models which
TDA9814 being used on models
IC601