— 13 —
When the
RF
bargraph falls below this tic mark during nor-
mal receiver operation, it initiates a Low Signal alarm and
causes
LOW SIGNAL
to flash on the LCD screen.
As a starting point, you might set the low-signal trigger
point about half the way down from the top of the
RF
bar-
graph, as shown above. This should allow for any signal
fading effects over the receive path, but will still alert the
user to a loss of carrier.
Push the knob again.
HI
and the right-hand tic mark will
blink. Turn the knob to set that tic mark (and its numerical
value) to a point that the carrier level must come back up to
for the alarm to reset, maybe a few segments above the left
tic mark. Push the knob again to set these points in
memory and to release the menu.
The alarm flashes
LOW SIGNAL
on the front-panel LCD and
activates the rear-panel
L
(low signal) terminal. Refer to
Pages 8 and 24 for using and programming this terminal.
Audio Muting
(Menu Screen 3)
Mute on Low Sig:
is a ‘squelch’ function that mutes the
audio outputs during a Low Signal alarm condition. This is
most useful when the INOmini 673 is used as a rebroadcast
‘translator’ receiver in its FM reception mode. This prevents
rebroadcasting the loud hissing sound characteristic of an
FM receiver when no signal is present. To enable muting,
push the knob and select either
On
or
Off
for this option.
Keep in mind that with this option set to
Off
, even a com-
plete loss of carrier will not initiate a simultaneous Audio
Loss alarm.
Signal-to-Noise and Multipath
(Menu Screen 4)
These are two additional indicators of signal quality, and
numerical values are assigned to each of these readouts as
well. The numbers are relative and take several metrics into
account.
SN
is a first-order approximation of the signal-to-noise ratio
of the received FM signal. The number does not signify any-
thing concrete, but certainly “more is better.”
Likewise,
MP
gives a relative indication of multipath (signal
reflection) effects that radio transmissions encounter on
— 14 —
their trip to the receiver, which introduce noise and distor-
tion into the audio. The object here is to keep
MP
as low as
possible.
00
is ideal and should be attainable when receiv-
ing a solid signal.
RF
,
SN
and
MP
numerical values are handy when installing a
rooftop antenna. In locating and aiming the antenna, do
everything you can to maximize
RF
and
SN
, and to minimize
MP
.
FM Stereo Mode
(Menu Screen 5)
When monitoring the analog FM transmission, there is a
choice of how the receiver handles FM-stereo decoding.
Stereo
is the default and obvious choice for a local, strong
station. The graphic on the second line of this menu is a
static graphic representation of the maximally-wide image
that characterizes a normal stereo transmission. When the
stereo pilot is lost, the display will collapse to the center.
Stereo-FM suffers a theo-
retical noise disad-
vantage of about 20dB
when compared with
monaural
broadcasts.
Push the knob and turn
it to select
Blend-St
.
This mode will mitigate the noise situation substantially by
progressively ‘blending’ the stereo image to mono as the FM
signal deteriorates under low-signal, multipath or other re-
ception handicaps. This mode is identified with
FM:B
in
Menu Screen 1.
In the blended mode the bargraph on the second line in this
menu does, in fact, depict a ‘dynamic stereo image.’ As the
circuit blends between full stereo and full mono, the actual
blending action will be indicated by a proportional narrow-
ing of the bargraph.
The degree of blending is not indicated on Menu Screen 1,
nor will the screen indicate
FM:M
if the transmission reverts
to full monaural when
Blend-St
is selected.
The stereo decoder may also be disabled, which will display
F-Mono
on this menu and
FM:M
on Menu Screen 1. This
puts the receiver in a Forced Monaural mode, collapsing the
stereo width display accordingly. This might be desirable
