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attenuation slope is adjustable via an
analog control signal. This component
offers significantly increased versatility
under the widely-varied operating
conditions to which CATV systems
are subjected. An “intelligent” control
system can tune the voltage-variable
equalizer’s (VVE) frequency response
on the fly, continually adapting to
changes in operating parameters, and
maintaining peak system performance.
Figures 2 and 3 illustrate the
performance
of
a
simplified
hypothetical CATV system (consisting
of two Mini-Circuits PGA-106-75+
amplifiers and 100 feet of RG-6/U
coaxial cable). The red plot shows
the gain of this system without the
equalizer, and the blue plot shows the
gain of this system with Mini-Circuits’
VAEQ-1220-75+
voltage-variable
equalizer inserted. In this simulation, a
tuning voltage of 3.05 volts is applied
to the VVE through its control input.
In this hypothetical system, the VAEQ-
1220-75+ reduces a slope of about -20
dB to a nearly flat region. While this
model has a particularly flat response
within the DOCSIS 3.1 downstream
band—up to 1220 GHz (and change)—
it is also operable down to 5 MHz.
The VAEQ-1220-75+ is designed
for use in 75Ω systems and is
operable over the entire DOCSIS
that component performance varies
with temperature, manufacturing
tolerances, humidity, the installation
technician’s choice of breakfast on
the preceding Tuesday, and so on.
So, an equalizer that exhibits an
optimal attenuation slope for 300
feet of Manufacturer A’s coaxial cable,
roasting at high noon during a Texan
summer, might not work so well with
50 icicle-draped feet of Manufacturer
B’s cable in Maine. A designer may
choose to design into her or his system
a switchable bank of equalizers, which
may be inserted into the signal path as
necessary, but a discretized solution
like this can rapidly turn cumbersome.
Because the “amount” of positive
slope needed to effectively flatten the
gain of a particular system will vary
depending on cable length, amplifier
performance,
gain/attenuation
variations thereof over temperature,
and myriad other system parameters,
passive equalizers are applicable to
relatively narrow regimes of operating
conditions. A tunable solution, on the
other hand, would be highly desirable.
Mini-Circuits’ VAEQ-1220-75+ offers
exactly that—an equalizer whose
Figure 2: Hypothetical CATV transmission system including equalizer
Figure 2 Implementation of AT Safeguards
22 l New-Tech Magazine Europe