A Small Solution to a Big PIM Problem

Mike Scheafer at desk--thumb Mike Schaefer April 21, 2015

What’s the big deal in passive intermodulation (PIM)? PIM robs a network of the speed, efficiency and coverage needed to keep up with today’s wireless device users. Think about this—a one decibel (dB) degradation in uplink sensitivity equates to around 11 percent reduction in coverage! A poorly performing connector, for instance, can easily contribute much more than 1dB of PIM interference, and cause a hefty hit on network coverage.

Enter CommScope’s new 4.3-10 small connector series. The 4.3-10 connector interface certainly is smaller than the globally dominant 7-16 connectors used across the wireless space, but we’ve done small before. Type N connectors are small. The 4.1-9.5 connectors are small. So why do we need another interface?

Due to their rock-solid PIM performance and, yes, their small profile, 4.3-10 series interfaces are being adopted by a number of the biggest operators, and are being seriously considered by many more.

My mother used to say, “It’s what’s inside that counts.”
In the case of the 4.3-10, it’s absolutely true. While it may look just like the other small profile connectors, the difference is in the way the 4.3-10 makes electrical contact. The 4.3-10 connector uses radial contact rather than the axial type contact used widely by other available interfaces.

Interfaces utilizing axial contact have a key weakness: their mechanical and electrical planes are linked. In order to achieve optimal electrical contact, you have to simultaneously reach a high mechanical face-to-face contact between the mating interface bodies. Imagine pushing your two closed fists together, knuckle to knuckle, and then twisting your hands in opposite directions. If your knuckles aren’t pushed together enough, i.e. fully torqued, then you won’t get the proper contact pressure, your hands will slip apart, and in the case of an under-torqued connector…here comes the PIM. To add to the difficulty, the typical o-ring seal is located right in the same mechanical plane, and it requires a high torque level to compress. The 4.3-10 series separates the mechanical and electrical reference planes to solve this problem.

When the weak link is the installation, older designs fall short. Connectors can work great when installed correctly, but older designs come with caveats. You only get the designed PIM performance when you tighten it just right. In contrast, when mating devices with 4.3-10 connectors, installers of any skill level can easily initially finger-tighten the male coupling nut, finishing the job with less than a quarter rotation with a wrench because they don’t have to compress the o-ring. This is a far cry from the multiple wrench rotations and 30 newton-meter torque required by a 7-16 DIN connector (DIN = Deutsches Institut für Normung, the German national standards organization that defined the connector type commonly used today). The built-in ability to fully engage the mating interface, without high torque, simplifies installation and is part of this interface’s rock-solid PIM performance.

Now that we’ve established that PIM is the real story of the 4.3-10 series, we get to talk about the small profile. Equipment is doing more with less space. Multi-band antennas, filters and remote radio units, previously sporting two ports, are in the process of densification, now doing the job of four, six, and more units with 12+ ports. The 7-16 DINs simply take up too much space. While making something small isn’t new, the 4.3-10 series is the perfect combination of a rock-solid low-PIM and low-profile design. Check out our 4.3-10 Portfolio page on our website for more information. And please feel free to leave me a comment with any questions.

About the Author

Mike Scheafer at desk--thumb

Mike Schaefer

Mike Schaefer is a product line manager in the HELIAX Cable Products group, with 20 years experience in the wireless industry. He holds a bachelor’s degree in management, a professional development certificate in organizational leadership and an MBA in Marketing.