During stereo broadcast, the SCA subcarrier must be
locked either in-phase or in quadrature to the third
harmonic of the 19 kHz pilot tone. The tolerance of
the phase angle is ±10° measured at the modulation
input to the FM transmitter.
With no modulation other than the pilot tone, an
oscilloscope trigged from the 19kHz pilot tone
should display the waveform as seen to the right.
To minimize the amount of peak level that the RDS
subcarrier adds to the composite baseband, your
OPTIMOD’s RDS generator is locked in quadrature
with respect to the pilot tone, so the example
shown here is for reference only.
If your transmission system is broadcasting stereo
correctly, it will also correctly pass the phasing built
into your OPTIMOD’s SCA generator.
3-6: Pilot/SCA Phasing Scope Trace
µMPX
µMPX in its simplest form is AES-EBU digital audio sampled at 192 kHz. AES sampling is done at 44.1 or 48 kHz in
most all broadcast plants. µMPX allows the FM multiplex signal including baseband audio, pilot, stereo sub, RDS
and 67 kHz subcarriers to be processed and transmitted either directly at the transmitter site or from the studio
through a broadband wired or wireless IP STL.
As it is a composite signal, the adjustments are familiar. The 5950 offers up to four destination points for the
µMPX signal. This can be useful when one processor is feeding multiple transmitter sites in a network.
You will need an audio transport method to transmit this signal and a receiver that will accept the Digital MPX
signal. For more information on equipment that is compatible with µMPX, feel free to contact Orban support at
support@orban.com
TEST
The Test Modes screen allows you to switch between OPERATE, BYPASS, and TONE. When you switch to BYPASS or TONE,
the preset you have on air is saved and will be restored when you switch back to OPERATE.
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