During PRESET, SCAN and FAST MANUAL tuning modes,
muting is always activated by digital signals from the tuning
system. Muting is also commanded by the IRIS remote
control system, as explained later.
For
“DXing”,
i.e. searching for extremely distant stations,
you may elect to de-activate the AUDIO-MUTING system,
for SLOW MANUAL station “searching”.
Depressing the MUTE OFF switch
(12)
allows your tuner to
reproduce all detected audio signals regardless of signal
strength or quality. You will now hear everything--very
weak stations, noise, mis-tuned stations etc.--except
during PRESET, SCAN or FAST MANUAL tuning , as dis-
cussed above.
When MUTE OFF is depressed, you can hear stations too
weak to activate the STATION DETECTOR logic, even
when in its most sensitive mode-(DISTANT STATION
switch in). When signals are this weak, the
SIGNAL-
STRENGTH BAR LIGHT (16), and the STEREO LIGHT
(20)
are intentionally blanked--to avoid display presentations
which are erratic, deceptive and annoying.
~(13) BLEND OFF
The depression of the BLEND OFF switch
(13)
de-activates
an automatic noise-reduction circuit which progressively
“blends” the stereo channels when the FM signal falls to
insufficient levels to achieve acceptable quieting in the
maximum-separation stereophonic mode.
This characteristic of stereo reception is related to two
factors. First, stereo transmissions carry more information
than mono transmissions. Second, this additional separa-
tion information is carried on a high frequency subcarrier
modulating the basic FM signal at frequencies well above
the audio band.
This subcarrier separation information is far more suscep-
tible to noise intrusion on weak signals than the basic
monaural (Left + Right) signal carried at audio (modulat-
ing) frequencies.
Thus, as signal strength falls to levels unable to maintain
acceptable signal-to-noise ratio in full-separation stereo
format, it is desirable and common practice to progressive-
ly blend the two stereo channels together, only as much as
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