Inovonics AARON 650, Инструкция по установке и эксплуатации

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prevents pilot modulation and RDS perturbations at any clip-
ping depth.
From the Main Menu, navi-
gate to: Setup / MPX output .
This data-entry screen is
where you set the final peak-
to-peak amplitude of the
MPX 1
and
MPX 2
outputs. The
Clipping
slider adjustment allows
anywhere from –2dB to +3dB of composite clipping, which re-
quires a bit of further explanation.
The composite/MPX signal level at this point in the circuit is at
a specific peak-to-peak level that assumes ±75kHz of stereo-
encoded carrier deviation. The audio program components
(without pilot and RDS in this case) will be right at the clipper
threshold when Clipping is set to 0dB. If peak deviations of the
incoming carrier are strictly held to “100% modulation,” the
clipper will never touch the program waveform.
The
program peak level of a monaural broadcast will be about
1dB higher than a stereo transmission, simply from the lack of
19kHz stereo pilot modulation. The
Clipping
control in this case
would thus be set to –1dB, assuming ±75kHz deviation of the
(mono) carrier.
In the real world, however, this assumption may be naïve. For
example, FCC regulations in the US permit a bit of over-
deviation when data and audio subcarriers are present. Moreo-
ver, enthusiastic broadcasters in competitive markets occasion-
ally ‘speed’ a bit, subcarriers or not. This is why the Clipping ad-
justment has a plus-and-minus range (plus for more clipping,
minus for less), and why we suggest judicious use of this con-
trol.
The obvious downside to composite clipping is the introduction
of ‘harmonics’ (harmonic and IM distortion products, actually)
within the audible spectrum and beyond. Use the MPX FFT dis-
play (Page 20) to help analyze possible problems associated
with use of this feature.
ALARMS
The AARON 650 includes alarms to apprise the user of these
signal reception problems: 1) Loss of audio, 2) Loss of Carrier
(or a drop in level) 3) RDS Error (subcarrier loss or ‘hijacking’),
and 4) Loss of Pilot (stereo loss). These alarms are indicated
on the front panel of the AARON 650 and are available as alarm
‘tallies’ (contact closures) on the rear panel. In addition, alarms
may be set up independently to send e-mail or text messages to
selected station personnel.
Carrier, audio and RES alarms may also be programmed to re-
place the off-air program with an alternative audio feed, either