— 11 —
analog display of levels between 10dBuV and 75dBuV. The
signal strength display does not refer to the dB scaling
above the display, which is used only for audio level meas-
urements in Menu Screen 7 for HD Radio reception or 8 for
FM.
The lower LCD scale is labeled
LOSIG:
and has a pair of tic
marks off to the right. Push the knob and
LO
, will begin to
blink, along with the left-hand tic mark. Turn the knob to
position the left tic mark anywhere beneath the
RF
bargraph. The tic mark level in dBuV is also displayed.
When the
RF
bargraph falls below this tic mark during nor-
mal receiver operation, it initiates a carrier-loss alarm and
causes
LOW SIGNAL
to flash on the LCD screen.
As a starting point, you might set the carrier-loss trigger
point about half the way down from the top of the
RF
bargraph, as shown in the illustration. This should allow
for typical signal fading over the receive path, but will still
alert the user to a valid carrier loss or transmitter power
problem.
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 rear-panel
C
terminal gives an NPN transistor satura-
tion to ground for a carrier-loss alarm; the polarity (logic
state) of the alarm is set on one of the hidden menu
screens, which are explained beginning on Page 20. This
ground may be used to actuate a relay, light an LED at a re-
mote location or tie-in with a remote control system.
Audio Muting
(Menu Screen 3)
Mute on Low Sig:
is a function that mutes the audio out-
puts during a low-signal alarm condition. This is most use-
ful when the INOmini 639 is used as a rebroadcast ‘transla-
tor’ receiver in its FM reception mode, preventing the re-
broadcasting of 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.
— 12 —
With this option set to
Off
, a carrier loss will generally not
initiate an audio loss alarm.
RF and HD Radio Signal Readouts
(Menu Screen 4)
RF:
is redundant to the similar measurement on Menu
Screen 2, a 0 to 75 numerical readout of the RF level in
dBµV at the antenna terminals. The bargraph represents
this entire range here.
HD:
indicates the relative power in the HD Radio carrier
portion of the FM channel spectrum. The numerical value
and bargraph cover a scale of 0 to 99. There is no hard-
and-fast rule governing the relationship of these side-by-
side measurements, though
HD:
will reflect the “dBc” injec-
tion level of the HD Radio carrier pair as well as reception
conditions.
Signal-to-Noise and Multipath
(Menu Screen 5)
These are two additional signal-quality indicators. Numeri-
cal values are assigned to each of these readouts as well,
but these numbers are relative and arbitrary, and do not re-
late to any fixed measurement parameter.
SN
is a first-order approximation of the signal-to-noise ratio
of the received FM signal. This measurement takes several
signal quality factors into account, but is strictly a relative
indication. The number does not signify anything concrete,
but certainly “more is better.”
Likewise,
MP
gives a relative indication of multipath (signal
reflection) effects that the transmission encounters on its
trip to the receiver. Multipath effects introduce noise and
distortion into FM programs and cause errors in digital sig-
nals that translate into dropouts and echoes. The object
here is to keep
MP
as low as possible.
00
is ideal and should
be attainable when receiving a solid signal.
RF
,
SN
and
MP
numerical values are handy metrics when in-
stalling a rooftop antenna. In locating and aiming the an-
tenna, do everything you can to maximize
RF
and
SN
, and to
minimize
MP
.
The Audio Loss Alarm
(Menu Screen 6)
Navigate to this screen and push the knob.
Audio Loss
will begin blinking. Turn the knob to dial-in the desired au-
