By Alan Vincent, Sales Director, Foremost Electronics For many years, the telecoms industry has had good support for Passive Intermodulation (PIM) testing with IEC62037-compliant test solutions using traditional two-tone carrier test methods. Unfortunately, these Field PIM test solutions can only test a single RF band and require the cell site to be out of service for the duration of the test, with the need to climb the tower and disconnect RF cables. With the growing number of RF bands and effective radiated power, higher system loads and cross-sector PIM, there is a growing number of PIM problems, impacting modern telecoms networks and needing new test solutions. PIM-over-CPRI Foremost Electronics’s customer AceAxis creates designs and technology to build, test and analyse telecoms networks, and is a pioneer in the development of remote radio head (RRH) technologies and embedded test and measurement solutions for this market. The company has developed a unique patented technology utilising PIM over Common Public Radio Interface, or CPRI, to address PIM testing in complex multi-band 4G and 5G networks. In addition, this unique PIM-over-CPRI solution is entirely passive, frequency-agnostic and can measure PIM whilst the cell site still operates, with measurements taken from the baseband unit, or BBU, typically located at the tower base, rooftop or BBU hotel. PIM testing setup The AceAxis PIM-over-CPRI product can accurately measure and locate PIM in live-cell sites using small portable test equipment (weighing less than a kilogram) that can be left at the cell site for long-term monitoring, if needed. The company has simplified the test process to ensure complex test conditions can be checked fast, simply and cost-effectively through an intuitive GUI and straightforward instructions. The GUI generates comprehensive reports that allows the network operator to evaluate the true impact of PIM in real traffic conditions. With PIM detection at its core, PIM Forensics is a software algorithm processing I/Q baseband signals on the front haul interface (CPRI link). Support given AceAxis approached Foremost Electronics requiring a case for a single-board device for PIM in complex multi-band 4G and 5G networks. The test system analyses the digital bitstream (I/Q data) on the fibre interface between the BBU and the remote radio head (RRH) to measure the effects of PIM. The enclosure had a number of very specific requirements: it had to be a compact customer-specific form-factor with a maintenance-free conduction cooling concept for high thermal performance without using fans. It required comprehensive EMC shielding and the integration of custom-developed rubber frames to protect the surface of the case, eliminating the use of conventional rubber feet, whilst ensuring a firm grip - even when the enclosures are stacked or placed on a workbench or table. As an added-value channel partner for nVent Schroff, Foremost has access to a very wide range of standard, customisable and complete, custom enclosure solutions and accessories. To shorten the development time for a non-standard case, Foremost decided to use products from the nVent Interscale case range for the AceAxis design. The Interscale enclosure range is a platform that provides a choice of enclosures with heights of 1, 2 or 3U, and with various widths and depths. It includes a wide palette of matched accessories, such as mounting plates for PCBs or fan kits, if required. The Interscale components selected provided simple customisation and excellent EMC protection, guaranteed because of a special locking mechanism of the side panels. As fan cooling was not permitted, a heat sink with a thermal pad to the processor was used to increase the cooling performance. The custom rubber frame assembly is screwless and easy to remove. Finally, the cases were painted to AceAxis’s requirements. The nVent Interscale is a very flexible electrical enclosure solution that can speed up integration times without incurring expensive tooling or NRE costs. The platform offered all the components required to meet the complex specification from AceAxis in a timely and cost-effective manner.