Transmission Levels; Line-Up Facilities; Metering Of Levels And Subjective Loudness; Figure 1-2: Absolute Peak Level, Vu And Ppm Reading - Orban OPTIMOD 6300 Operating Manual

OPTIMOD 6300 DIGITAL
In facilities that use the BBC-standard PPM, maximum program level is usually PPM4
for music, PPM6 for speech. Line-up level is usually PPM4, which corresponds to
+4dBu. Instantaneous peaks will reach +17dBu or more on voice.
In facilities that use PPMs that indicate level directly in dBu, maximum program and
line-up level is often +6dBu. Instantaneous peaks will reach +11dBu or more.

Transmission Levels

The transmission engineer is primarily concerned with the peak level of a program
to prevent overloading or over-modulation of the transmission system. This peak
overload level is defined differently, system to system.
In FM modulation (FM / VHF radio and television broadcast, microwave or analog
satellite links), it is the maximum-permitted RF carrier frequency deviation. In AM
modulation, it is negative carrier pinch-off. In analog telephone / post / PTT trans-
mission, it is the level above which serious crosstalk into other channels occurs, or
the level at which the amplifiers in the channel overload. In digital channels, it is the
largest possible digital word.
For metering, the transmission engineer uses an oscilloscope, absolute peak-sensing
meter, calibrated peak-sensing LED indicator, or a modulation meter. A modulation
meter usually has two components—a semi-peak reading meter (like a PPM), and a
peak-indicating light, which is calibrated to turn on whenever the instantaneous
peak modulation exceeds the overmodulation threshold.

Line-Up Facilities

Metering of Levels and Subjective Loudness

The meters on the 6300 show peak input levels, the peak output modulation, and

Figure 1-2: Absolute Peak Level, VU and PPM Reading

INTRODUCTION
ABSOLUTE PEAK
PPM
VU
1-21