1055497-1 Datasheet, PDF (283/320 Pages) Tyco Electronics – RF Coax Products

RF Coax Connectors
Appendix C - Intermodulation in RF Coaxial Connectors (Continued)
Remedies for IM in RF Coaxial Connectors (Continued)
potential of a butt-contact. Panel interfaces generally concern the
physical contact of the connector body to the panel. In this case,
it has been determined that a protruding feature as close as
possible to the body bore will give the best IM performance. The
applied mounting force is concentrated in the surface area of the
protrusion which, on engagement with the panel, punctures the
existing oxide layer to give a metal-to-metal, gas-tight junction.
■ _{Avoidance of crimps}
Crimps, by nature, can only give multiple point-contact rather
than 360-degree contact and also cause a variability in the
position of electrical contact during dynamic testing. IM prod-
ucts will therefore be greater. It has been found that soldered
center contacts and clamp/solder outer contacts give the best
static and dynamic IM performance.
Improving IM Connector Design
Tyco Electronics continues to pursue design techniques which
improve intermodulation performance to address emerging
telecommunication market needs. A state of the art intermodu-
lation test facility and participation on the international (IEC
SC46D WG5) committee to develop standard test practices
ensures our commitment to the understanding of intermodula-
tion characteristics. This applied technology base is instrumen-
tal in developing innovative low intermodulation products for
7-16, Type N, SMA and OSP interfaces.
Most commonly asked questions regarding Intermodulation
1. Why is intermodulation such a concern for cellular
infrastructure equipment?
The primary concerns for cellular service providers today
are channel efficiency and clarity of transmission. Growth in
demand for mobile communications has created a need to
operate equipment at greater capacities and reliability to
service the competitive market. Intermodulation degrades or
limits the ability of the service provider to operate at optimal
levels of performance and may ultimately cause subscribers
to experience poor call quality. Intermodulation has become
an important factor in system selection to ensure the best
possible network service.
2. Where is intermodulation most likely to occur in cellular
infrastructure equipment?
Intermodulation is typically of greatest concern between the
filtering elements of the system and the antenna. The introduc-
tion of higher power levels for the transmit side of the equip-
ment creates greater potential for intermodulation to occur.
This is why the majority of focus for intermodulation concerns
7-16, Type N, SMA and 4.1/9.5 connector interfaces.
3. Is intermodulation a recent development?
Intermodulation has always been inherently present in RF coax-
ial connectors but may be relatively imperceptible in some
devices for a variety of reasons. The amount of power applied
to an RF connector determines the relative IM threshold which
can be observed. Intermodulation is therefore more likely to
cause concern in a higher power system, for example, utilizing
a 7-16 connector interface rather than an equivalent low power
OSX solution. The trend toward higher power digital cellular
systems creates the need for greater intermodulation sensitivity.
4. What is the best method of cable attachment for IM sensi-
tive cable assembly applications?
Soldering and clamping are preferred methods due to the
360-degree point of contact created at the cable to connector
interface. Such intimate contact improves the overall contact
resistance leading to improved IM characteristics. In addition,
it is also better to solder the center conductor of the connector
to the cable versus crimping due to the improved contact
resistance path and elimination of voids.
5. Are there ways to test for intermodulation in an RF coaxial
connector?
Yes, very sophisticated methods are needed to test for inter-
modulation in RF connectors. The test system must utilize
extremely sensitive filtering or clean amplification so that the
equipment itself has a very low intermodulation noise floor.
There is not yet a standardized approach to testing, although
an international committee has been formed in the connector
industry to address the situation. Tyco Electronics has a state
of the art test facility where our designs are optimized for low
intermod performance and where further analysis on the
effects of this phenomena can be studied.
6. Is intermodulation in coaxial connectors frequency
dependent?
No. Because coaxial connectors are broadband devices there
is no frequency dependency. Some apparent variability can
be detected during testing but this is not due to the connector.
The impedance matches of the output diplexer/triplexer and
terminations are the causes of the variations and should not
be incorrectly attributed to the connector/assembly.
Tyco Electronics Interconnect Business Unit has demonstrated
that by varying the impedance match of the test station termi-
nation, a DUT can show 15dB better IMP₃ than exists in reality.
7. IMP3 in mixers follows a 3dB/dB relationship.
What is it for connectors?
The relationship is identical. Taking the 3rd order (2F1-F2):
varying the power of F2 gives an IMP₃ relationship of 1dB/dB
whereas varying the power of F1 gives a relationship of 2dB/dB
as the IMP is derived from the 2nd harmonic of F1. This gives a
total of 3dB/dB when symmetrically varying both carrier powers.
8. I am buying a complete cable assembly from
Tyco Electronics. How do I interpret the IMP result now?
With caution! It is the Tyco Electronics policy when testing
devices to move away from the normal static test to a dynamic
test where the cable termination interfaces are mechanically
exercised during live IM conditions. It is also a good indicator
to customers of the build quality of the assemblies. A dynamic
evaluation has shown 15dB degradation in IMP performance
for poor assemblies and even as much as 50dB for bad
ones.It is therefore strongly advisable that IM performance fig-
ures are stated in the context of a dynamic measurement.
Catalog 1307191
Revised 3-07
www.tycoelectronics.com
Dimensions are in millimeters
and inches unless otherwise
specified. Values in brackets
are standard equivalents.
Dimensions are shown for
reference purposes only.
Specifications subject
to change.
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283
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