Figure 5: Filters for different combinations of low (<10Ω) and
high (>100Ω) source and load impedances.
(Image Source: EMP Connectors)
A connector can include a variety of filter topologies,
as shown in Figure 5. A single capacitor inserted between
the signal line and ground is the simplest and lowest cost
option, and has good low-frequency performance; the
performance of LC-type filters is excellent if the source
impedance is less that the load impedance.
A connector can incorporate more sophisticated filters
by stacking planar arrays. For example, the Pi filter is
popular in MF, VHF, and UHF applications since it has
a steep insertion loss curve for frequencies above 10Mz.
TE Connectivity’s Deutsch filter connector family even
includes a double-T filter option with three inductors and
Whenever a component such as a connector is inserted
into the signal path between source and destination,
it causes a degradation of the signal: insertion loss,
expressed in dB, is a measure of this degradation.
A filter connector’s job is to remove unwanted noise,
but in doing so it may also attenuate a portion of the
desired signal. It’s important to minimize insertion loss
over the frequency range of interest: even though the
post-connector signal can be amplified, too large an
insertion loss may result in an unacceptable degradation of
system performance. Each filter type has a characteristic
insertion loss over the target frequency range, as shown in
Figure 6: Comparison of insertion losses for different filter types.
(Image Source: Connect Solutions)
Specifying a filter connector from the start of the
project may be preferred, but its increased cost may
preclude use in many applications. If EMC problems
occur in the field, a retrofit solution may be the
answer. Quell, for example, offers versions of its
EESeal filter insert for numerous connectors, including
circular MIL-C-26482, MIL-C-38999, MIL-C-5015,
MIL-C-83723 connectors, plus ARINC, DIN,
subminiature D, and custom designs. The technology
limits fast transients by embedding discrete filter
components in an elastomeric shell; the component
connects between the pin and the outer edge of the
insert, which shorts to the connector shell ground.
Capacitors up to 1μF, resistors, MOVs, and diodes
are available; some models can include more than one
component per pin.
The military and the avionics industry are both
major users of filter connectors, so circular MIL-STD and ARINC connectors constitute the bulk
of most product catalogs. Both customers use
filtered connectors to ensure the reliable operation
of communication and navigation equipment; the
military must also protect both its aircraft and ground
vehicles against EMP attacks.
Let’s hope the aliens don’t have photon torpedoes. ECN
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