Comtech EF Data EQ90 Series - Manual (Page 47)

EQ90 Amplitude Equalizer Operation
Rev. 2 3-23
The amount of frequency shift is directly proportional to the amount of frequency offset.
For example:
•
A section tuned to 80 MHz would have to be offset twice as much as one tuned
to 70 MHz.
•
Sections tuned to 70 MHz require no frequency adjustment.
•
Sections below 70 MHz require the same treatment as those tuned above 70
MHz, except in the opposite frequency direction.
•
These adjustments affect the magnitude of delay without greatly affecting the
delay shape.
The same effect can be achieved by reducing or increasing each equalizer section delay,
depending upon its particular frequency location. Although the overall effect is the same,
adjusting delay magnitude also has the effect of changing frequency of the delay section,
which complicates the adjustment process. The order of adjustment should be:
1. Eliminate linear delay.
2. Eliminate parabolic delay.
3. Reduce delay ripple.
Reduction of the magnitude of delay ripple will require adjustments of the delay
magnitude and frequency of equalizer sections, which are centered near the frequency of
the delay ripple. This process is slow and tedious, and will require many trial and error
attempts before the ripple magnitude is below acceptable levels. It is advisable during the
adjustment process to maintain a record of adjustments made so that backtracking is
possible if a series of adjustments yields poor results.
The delay characteristics discussed to this point have been largely parabolic in shape,
which is ideal for equalization. Actual transponder delays may appear more trapezoidal,
as shown in Figure Chapter 3-28, with straight-line segments. Figure Chapter 3-29 and
Figure Chapter 3-30 demonstrates the effect of an equalizer frequency offset. By using
straight line approximations of the actual characteristics, one can determine the cause of
the composite response shape and thus arrive at a correct course of action to obtain a
delay equalized composite response.
After the satellite delay characteristic has been properly equalized, it will be necessary to
adjust the equalizer for a flat amplitude characteristic. This is best accomplished on the
equalizer itself using an MLA.
Once the equalization and amplitude adjustments have been completed it is advisable to
record the amplitude and delay characteristic of each section of each equalizer module by
itself so that a backup or replacement equalizer module can be properly set without
resorting to removing traffic from the satellite transmission path.