Subcarrier Injection Level; Setting Subcarrier Amplitude - DEVA Broadcast SmartGen Mini Maintenance And Operation Instruction Manual

In the sidechain mode of operation, the RDS subcarrier is the only signal that appears at the
rear-panel RDS OR MPX OUTPUT connector. Because some exciters require a high signal level at
auxiliary wideband (SCA) inputs, the RDS signal has been made adjustable to any value between
zero and 4 volts, peak-to-peak.
In loop-through operation of the encoder, the composite/MPX program signal that is fed to
the PILOT OR MPX INPUT appears with unity gain at the RDS OR MPX OUTPUT. A typical
peak-to-peak level of the Composite/MPX program signal is up to 10dBu. The same 0-4V RDS
subcarrier level range is available in this mode.

SETTING SUBCARRIER AMPLITUDE

Injection level is best set with a modulation monitor that includes a subcarrier measurement
utility. Alternatively, a basic mod-monitor can be used alone, but program modulation and the
stereo pilot must be turned off to resolve the low RDS injection level.
NOTE: If using a mod-monitor that does not have separate subcarrier measurement ability,
keep in mind that mod-monitors are peak-responding for total modulation readings near 100%
modulation, but may be average-responding for measurements at low levels of modulation.
Because the RDS subcarrier is a complex, suppressed-carrier double-sideband signal, an average
reading of 3% RDS injection can represent a level that is substantially higher when measured
peak-to-peak. It is the peak level we are interested in with broadcasting.
Perhaps a better means of setting injection when a subcarrier monitor is not available is simply
to bridge the input of the exciter with an oscilloscope using a BNC "T" adapter. With the audio
program muted, the peak-to-peak value of the 19kHz stereo pilot signal can be noted. With this
figure in mind, turn off pilot modulation (but do not disconnect the stereo generator) and set
the peak-to-peak value of the RDS subcarrier to about one-third of the measured 19kHz pilot
level. When programming is restored, the mod-monitor should indicate a 3% increase in total
modulation, though this may be difficult to resolve near the 100% mark. Readjust the output level
of the stereo generator to fine-tune the original total-mod figure.
In the United States, the FCC permits an extra 5% modulation for each subcarrier, with total
modulation not to exceed 110% even with two or more subcarriers.

Subcarrier Injection Level

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