— 11 —
right-hand corner. A series of bars to the right of
RF
will
give a rudimentary display of incoming carrier strength.
If the station is transmit-
ting an RDS (Radio Data
System) subcarrier, the
station PI (Program Iden-
tification) hexadecimal
code will appear on the
LCD screen below
FREQ
. In North America, where the PI
code is actually derived from station call letters, those call
letters will be decoded and displayed to the right of the PI
hex value.
Once the receiver is tuned, push the jog wheel.
FREQ
will
stop blinking and the tuned frequency will be transferred
into non-volatile memory. This releases the jog wheel to
navigate to other menus.
Carrier Strength and Alarm
(Menu Screen 2)
The
RF
bargraph at the
top of this menu screen
shows incoming signal
level. There is an
RF
numerical value given as
well, but this number
represents only the number of active bargraph segments,
which can be used as a comparative reference. This display
is simply a
relative
indication of the FM carrier strength and
has no association with the dB scale beside the LCD win-
dow. The dB scales are used only for audio level measure-
ments in Menu Screen 5.
The lower LCD scale is labeled
LOSIG:
and has a single tic
mark off to the right. Push the jog wheel and
LOSIG
will
begin to blink. As you turn the knob note that the single tic
mark can be positioned anywhere beneath the
RF
bargraph.
During normal receiver operation, whenever the
RF:
bar-
graph falls below the tic mark,
LOW SIGNAL
will flash on the
LCD screen and a carrier-loss alarm will be sent to the rear-
panel connector. The rear-panel
C
terminal gives an NPN
transistor saturation to ground on this alarm, which may be
used to actuate a relay, light a remote LED indicator or tie
into a remote control system.
— 12 —
As a starting point, you might set the carrier-loss trigger
point about a quarter of the way down from the top of the
RF
bargraph, as in the illustration above. 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. Your actual setting may need to take additional
factors into account, but when the proper trigger point has
been determined and set, push the knob again to fix the
alarm point in memory and to release the menu.
Signal-to-Noise and Multipath
(Menu Screen 3)
This screen displays two additional signal-quality measure-
ments. Numerical values are assigned to each of these
readouts as well, but again signify only the number of active
bargraph segments.
SN
is a first-order approximation of the signal-to-noise qual-
ity of the tuned signal. This measurement takes several
signal quality factors into account, but is strictly a relative
indication. No hard-and-fast rule can be derived from this
display, except for “more is better.”
Similarly,
MP
gives a relative indication of the multipath
(signal reflection) effects that the transmission encounters
in its trip to the receiver. Multipath distortion is an im-
portant factor in the quality of the recovered audio program
with respect to noise and other audible artifacts. The object
here is to keep
MP
as low as possible. Zero would be nice
and should be attainable when a good signal is received.
The
SN
and
MP
numerical values are handy to keep track of
when installing a rooftop or tower-mounted antenna. In lo-
cating, orientating and aiming the antenna, do everything
you can to maximize
SN
and minimize
MP
.
The Audio Loss Alarm
(Menu Screen 4A)
Navigate to this Screen
and push the knob.
A-LOSS:
will begin to
blink. Turn the knob to
dial-in the desired audio
loss alarm delay time,
which is the time in seconds between the onset of ‘dead air’
and a flashing LCD and rear-panel alarm. The delay may be
programmed in one-second increments up to 2 minutes.
