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Explore pre-compliance testing for WLAN transmitters

Posted: 08 Jul 2014  Print Version  Bookmark and Share

Keywords:Internet of Things  WLAN  pre-compliance testing  EMI measurement  IEEE 802.11 

Being just a smart gadget is no longer enough. Any device that wants to grab consumer attention has to be both smart and connected. The connected piece means that wireless must be part of the design as well. Wireless also opens up many new design possibilities and is starting to show up in some unusual places. Here are a couple of the more interesting examples.

Start-up Velo Labs is developing a solar-powered bike lock that can hook up to Wi-Fi networks to send alerts to the bicycle owner's smartphone if the lock's motion detector senses that the bicycle is potentially being stolen.

A new intelligent electric toothbrush from Oral-B incorporates wireless to capture information about the user's brushing habits where it presumably could become part of dental records. The question of whether or not this is a good thing is up to the consumer to decide.

The point here, of course, is that there are thousands of products on the shelves, in the works, or yet to be imagined that will incorporate low-power wireless capability to meet consumer demand or to become part of the so-called Internet of Things.

Figure 1: Using a wireless module lowers design complexity, but still involves a number of important steps, the most critical being ensuring that the design passes regulatory compliance tests.

One challenging part of this demand for connectedness is that product manufacturers – many of whom have little to no RF experience – need to learn how to add wireless capability to their products. The most common and practical approach is to incorporate a prepackaged WLAN module into your design. Not surprisingly, the market for such modules is growing at a double digit pace, with continued growth forecast.

While the use of wireless modules eliminates many technical issues, there are still many decisions to be made (figure 1). The most critical – and daunting – task is to ensure that the end product meets complex FCC and international regulatory requirements. Compliance testing is exhaustive and time consuming, and a failure at this stage of product development can cause expensive re-design and delay product introduction.

Regulatory pre-compliance checks, as highlighted in step 6 of the flowchart, are vital to avoiding such worse-case scenarios. Fortunately, cost-effective and familiar test equipment can be used in-house to perform pre-compliance testing and ensure that your wireless-enabled products have a high probability of passing compliance tests on the first go round. The goal is to uncover potential problems early on and reduce the risk of costly failure at the compliance test stage.

From the very first wireless transmissions, spectrum emission has been a concern for design engineers. Regulatory agencies around the world have placed limits on the emission levels, and have defined measurement methods for compliance testing. Formal certification, which must be completed before a product can be sold, must be done at an independent lab and can cost between $5,000 to $10,000 per day not including travel and other expenses.

The use of off-the-shelf modules, even ones that have been certified on their own, doesn't necessarily make the job of obtaining certification much easier. This is because the complete assembly of the final product must be tested and qualified as well. Design issues like PC board layout, antenna design and placement or system interactions can lead to a product failing to meet certification requirements.

Sorting out these issues during the design phase is made much easier with instrumentation that not only lets designers perform a full range of pre-compliance testing on their own test bench, but also helps designers identify the root cause of problems that could cause a product to fail formal tests.

Pre-compliance testing vs. full compliance
Pre-compliance testing is done after system integration of the wireless module to determine any problem areas in the design. Pre-compliance testing doesn't necessarily need to map to every single international standard since the goal is to simply uncover potential problems and reduce risk of failure at the expensive compliance test stage. The equipment used also does not have to include every feature and specification required by the standard, and can have lower accuracy and dynamic range than compliant receivers if sufficient margin is applied to the test results.

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