TELE-audiovision - The World’s Largest Digital TV Trade Magazine - page 174

TELE-audiovision International — The World‘s Largest Digital TV Trade Magazine
— 1 -12/2013
Example with a UHF filter of a pay TV operator: The left picture shows the whole CATV
spectrum without any filter. The right picture shows the result of using a low pass filter
with a cut-off frequency of 296 MHz.
tive impact on neighbouring
frequencies. In addition, re-
ceivers and other active ele-
ments within the system are
at risk of malfunctioning due
to interference.
The trick now is to filter
out those unused frequency
ranges that carry the inter-
fering signals.
Existing signals can be fil-
tered in a number of differ-
ent ways. For one, it is possi-
ble to filter out signals above
and/or below a certain speci-
fied frequency. Low-pass and
high-pass filters are used to
that end. A low-pass filter
allows all frequencies below
the cut-off frequency, while a
high-pass filter lets through
all frequencies above a set
cut-off frequency. Unwanted
frequencies that are outside
the cut-off frequencies are
highly attenuated, whereas
the target frequency range
comes through with minimal
Now if you combine a high-
pass filter with low cut-off
frequency and a low-pass
filter with high cut-off fre-
quency it is even possible to
only allow a single frequency
range through the filter set-
up. The correct term for such
a configuration is band-pass
If, on the other hand, a
low-pass filter is used in con-
junction with a high-pass fil-
ter that has a higher cut-off
frequency, only the centre
frequency space is filtered
and what we get is a so-
called reject filter.
Then again, what’s the use
of all those filters? To start
with, they allow providing
individual frequency bands
to different receivers with-
out those receivers having to
share frequency bands. SCR
(Single Cable Routing) distri-
bution setups, for instance,
make use of this approach,
with up to eight receivers
having independent access
to all satellite channels via a
The new catalogue by MFC gives an extensive overview of all available filters made by MFC. The
catalogue can also be downloaded directly from their website:
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