MPX BOARD CONNECTIONS (FM VERSION ONLY)
ENG
Page 38
16.2 DEFAULT MPX BOARD CONFIGURATION
(FM-MPX VERSION ONLY)
When not otherwise specified, the MPX board comes with J2, J4 and J5 jumpers closed and with OUT-2
output disabled.
The AUX 2 input (BNC connector, 10 kOhm impedance) allows an external signal (tipically RDS) from an
external encoder to be injected on the MPX output of the processor.
The level of the injected RDS signal may be adjusted by means of the trimmer next to the corresponding
BNC connector. This trimmer is factor preset for a gain of 0 dB. The setting range is between -
∞
and +12 dB.
The AUX-1 input (BNC connector, 10 kOhm impedance) allows you to inject an external signal (tipically
SCA) from an external device on the MPX processor output.
The level of the injected SCA signal may be adjusted by means of the trimmer next to the corresponding
BNC connector. This trimmer is factor preset for a gain of 0 dB. The setting range is between -inf and +12
dB.
The processor can mix SCA signals of any frequency with its own MPX signal, as long as
the former are compatible with the composite stereo signal and RDS signal spectra. The
RDS encoder inside the processor must be disabled before using an external RDS
encoder.
The MPX OUT 1 (BNC connector) provides the FM composite any RDS signal (internally generated
or injected from an external encoder) and SCA signal.
An hardware bypass directly connects the AUX-1 connector to the MPX OUT-1 connector in
the event of Main AC failure. The hardware bypass is achieved through the Relè 1 (see
block diagram).
Remarks:
-
The stereo multiplex output level is adjusted by a rear panel multiturn precision trimmer. The level is adjustable
from
-inf to +12dBm
(8.8 Vpp) at 100% modulation
. Factory preset is 0 dBm, i.e. approximately 2.2 Vpp.
-
The output impedance of the BNC jack is approximately 10 ohms sourced by an output driver capable to drive
600
Ohm loads (typical). Maximum performance is achievable when using up to 10 meters of RG-58 cable.
Alternatively, 75 Ohm cable may also used for short runs.
-
Contrary to Left / Right audio outputs, pre-emphasis is always present on the MPX output and you
can NOT disable it. Nevertheless, the menu allows you to set the pre-emphasis time to 50 or 75
μ
sec.
(see par 19.12).
-
The 19 kHz pilot phase and level may be adjusted via the menu (19.13).
-
MPX Out provides a reference tone consisting of a 400 Hz / 0 dBm pilot tone of 19 kHz / - 20
dBm. This tone corresponds to the maximum frequency deviation of 75KHz. To enable the reference
tone, see chapter 20.7.
-
The processor has a built-in automatic composite clipper, not adjustable by the user.
The MPX OUT 1 TEST connector provides a repetition of the output signal appearing at the main MPX OUT
1 connector, with the same level. The TEST output is individually buffered so that a short circuit on one
output will not affect the other. The TEST output is mainly designed to allow easy and fast measurement on
the main MPX signal being output by the processor, without alterating it.
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