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4.2
CONTROLS
4.2.1. Power Control Switch
. This switch controls mains power to all the
circuits in the tuner when turned ON. When turned OFF it
disconnects all mains power from all tuner circuits.
4.2.2. Preset Switch
. In the normal position, this switch enables the
manual tuning control knob for selection of stations. The remaining
four positions of the switch enable the four pre-set stations. As
the switch is moved to each position it uncovers the associated
pre-set. These pre-sets can be turned to particular stations by
turning them with a small screwdriver or trimmer.
4.2.3. Muting Switch
. This switch enables the muting circuit, which mutes
the tuner output for very weak signals so that inter-station hiss
is not heard. When it is set to OFF all signals are fed to the
output regardless of their quality. If the switch is set to ON when
the SFM2 is tuned more than 40KHz from a station centre frequency the
output will be muted in this mode. The Tuner is muted at any time that
the 'ON Channel' LED is extinguished. Due to the narrow tuning window
for each station with Mute ON, we recommend that tuning is carried out
very slowly to avoid over shooting station centres.
4.2.4. Stereo/Mono Switch. This switch is normally set to STEREO position
which enables stereo stations to be received if they are of a suitable
signal strength; during reception of MONO signals (having no 19KHz
Stereo Pilot Tone) the tuner automatically reverts to the mono mode.
The centre position is STEREO BLEND which reduces the noise level when
a stereo signal is received but at the expense of some stereo
separation. The third position is MONO. When the switch is set at
MONO it is not possible to receive any programmes in stereo. Note that
adequate reception of stereo programmes requires a much larger signal
than that necessary for good mono reception.
4.2.5. De-emphasis Switch. In the normal position of this switch the de-
emphasis time constant is set to that suitable for the area in which
the tuner is used. In the second position the de-emphasis is
recommended whenever Dolby* encoded signals are received and enables
the signal of the correct frequency content to be fed to an external
Dolby type B decoder.
4.2.6. AFC Switch. This switch, the automatic frequency control switch, is
normally set to OFF when the tune control is operated. Once the station
has been selected, setting the switch to ON activates the circuit which
automatically holds the tuner onto the selected station and
compensates for slight manual mis-tuning or any tendency for the tuner
to drift off the station.
4.2.7.
Tuning
Control
. This manual tuning control is a ten-turn rotary
potentiometer which sets the tuner to receive any frequency on the VHF
band from 88 Megahertz to 108 Megahertz.
4.2.8. Preset Volume Controls. (Located on the rear panel). These are used to
match the audio output of the tuner to the inputs of ancillary
equipment such as amplifiers or tape recorders.
* Trademark of Dolby Laboratories Inc.
