Example 4. What are the delays at 2.1 kHz?
Solution: Uncorrected delay (point D) = 1.6 ms.
Inserted delay (point C) = 1.9 ms.
Corrected delay (point F) = 3.5 ms.
b. Block Diagram.
Figure 4-4 shows the block diagram of a typical
combination equalizer that is designed to compensate for both amplitude-
frequency distortion and envelope delay. It is similar to a simple amplitude-
frequency equalizer, but it contains 12 equalizer sections, each capable of
equalizing a small segment of the frequency spectrum in the voice range. Each
section is tunable so that selected segments of the spectrum may be equalized
independently. Not all sections need be used; the number required depends on
the parameters specified for the service and the characteristics of the
transmission facilities. For simple voice communication an equalizer may not
be necessary, but if the circuit is to be switched for services requiring
conditioning, the number of equalizer sections will be chosen to satisfy the
highest type of service to be placed on that circuit. For data transmission an
equalizer is essential, with most of the sections being used.
Figure 4-4.
Combination equalizer, block diagram.
c. Equalizer Section. One of the 12 equalizer sections is shown in figure
4-5. The frequency can be adjusted to locate the point where equalization is
most needed within the narrow spectrum selected by the section. Envelope delay
can be adjusted to make all delays equal in the 12 sections (or number of
sections used).
Amplitude can be adjusted so that the output level of each
section has an approximately equal value.
The circuit conditioner will find
that variation in any of the three controls (frequency, delay, or amplitude)
has an
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