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Overload measurement.

  1. Overload
  2. ROLE-TYPES, ROLE CONFLICTS, ROLE OVERLOADS

The overload point is precisely defined according to one of two definitions, using harmonic/intermodulation products or using gain change.

20.9.1.1 Harmonic/intermodulation products

CCITT (1985) Recommendation G223, defines the overload as:

'The overload point or overload level of an amplifier is at that value of absolute power at the output at which the absolute power level of the third harmonic increases by 20dB when the input signal to the amplifier is increased by ldB.'

If the 3rd harmonic is outside the frequency band of interest then the 2A-B intermodulation product may be used instead of the 3rd harmonic by the definition:

'The overload point or overload level of an amplifier is 6dB higher than the absolute power level in dBm, at the output of the amplifier, of each of two sinusoid signals of equal amplitude and of frequency A and B respectively, when these absolute power levels are so adjusted that an increase in ldB of both of their separate levels at the input of the amplifier cause an increase, at the output of the amplifier, of 20dB in the intermodulation product of 2A-B.'

20.9.1.2 Gain change

From Equation 20.13 it can be seen the gain to the fundamental signal decreases by a factor given by expression 20.35 due to the non-linear characteristic.

This effect can be used to give a definition of overload such that:

'The overload is the output power in dBm longest proposed international link is 25000km (CCITT,1985, G.I 03) and is constructed of a number of sub hypothetical links of typically 2500km.

The advantage of this last method is that it is easy to perform and can be measured at any frequency in the band of interest.



Overload | Noise contributions

FDM principles | Bell system | Frequency translation | Carrier frequency accuracy | Translation equipment pilots | Line equipment pilots | Definitions | Thermal noise | Noise due to unlinearity | Measurement of noise contributions |

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