Series BF
Split Ferrite Suppressors for Round Cables
SUPPRESSORS
2/2002
PAG E
111
www.delevan.com
E-mail: apisales@delev an.com
270 Quaker Rd., East Aurora NY 14052 • Phone 716-652-3600 • Fax 716-652-4814
Electronic cables and wires, by virtue of their length-to-width
ratios , are perfect natural antennas. In the presence of high
speed microprocessor signals,
cables will conduct, r adiate
and/or receive unwanted
high frequency interf ering
signals. Radio interference
sources usually radiate their RFI
pow er at frequencies abo ve 30
MHz by way of the
main cabling, which
acts as an antenna.
Control of radio
interf erence can be
assured by proper
placement of an insertion
loss de vice , such as a ferrite
suppressor. Any device used to
block an RFI signal between its source and a receiv er is an
electromagnetic interf erence (EMI) shield. The measure of
this ability to attenuate RFI is shielding effectiveness , "SE",
which is e xpressed in decibels , "dB", the r atio of field
strength on one side of the shield to the other side.
One of the most versatile and cost effective shielding
methods that can be used
toda y is the API Delevan
bisected f errite cable snap
assembly. The bisected
styling, or f amiliar
clamshell enclosure
design off ers the ultimate
in adaptability. The RF
absorbing and material
interacts directly with
unwanted high frequency energy and
dissipates it eff ectively while allowing data signals to pass
unimpeded.
Bisected f errites have a concentrated, homogeneous
magnetic structure with high permeability. These are
consistently stable at +20°C to +60°C and provide RF
suppression without eddy current losses.
AIR GAP EFFECT
The air gap in bisected f errites actually e xtends current
carrying capabilities with only an extremely small reduction
in impedance versus solid ferrites of the same size. The gap
is magnetically insignificant while it is electrically significant
as a discontinuation, thereb y accommodating more current.
POSITION OF SUPPRESSOR The suppressor should
normally be located close to the cable termination where it exits
the enclosure. Where a cab le connects tw o enclosures
containing RF sources, a suppressor on each end ma y be
required. F or circuits within an enclosure, a position close to the
RF is best. How e v er, other locations along the circuit ma y w ork
as well.
Material and U .L. Data API-1 Material, see characteristics
and inf ormation on page 118