Lesson 1/Learning Event 3
Attenuation can be defined as loss of signal power, and may be
classed as either intentional or unintentional. Loss of signal power can
be attributed, in most cases, to impedance mismatch (reflection loss) and
to heat loss. Reflection loss is unintentional as is also heat loss due
to resistance in lines. However, heat loss is intentional when values of
Heat loss is usually
of many parts which must be connected together by means of telephone lines
Each element of the system has a given input and
output impedance which must be matched to the line facilities.
minimum loss, and to prevent reflection loss with consequent phase
distortion of the signal elements.
(1) Maximum transfer of power is demonstrated in figure 1-2 by three
simple DC circuits consisting of a battery and two resistors.
and R2 the load impedance. The battery represents the source of energy.
Calculations shown on the figure prove that power (0.24 watt) delivered to
the load is greatest when impedances are matched (both 600 ohms).
load impedance is greater or lower than source impedance, power delivered
to the load is reduced (0.18) watt.
Maximum Power Transfer from Source to Load.