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What causes a PIM and how PIM testing works

TMG test Equipment | What is PIM Testing?
In this blog, we investigate what causes a PIM and how PIM testing works.

What is PIM Testing

Passive intermodulation (PIM) can create interference with cellular communications. It reduces receiver sensitivity or effectively hinders communication entirely. In turn, this affects the signal that the device was making to begin with as well as any receivers nearby.

Though PIM can appear in wireless devices, especially cellular ones, you can conduct PIM testing with the right equipment to mitigate the consequences of PIM.

PIM testing can help you test your cellular device or antenna for any PIM activity, so that you can remedy your signals and have a fully functioning cellular device or antenna.

In this blog, we investigate what causes a PIM and how PIM testing works.

What Causes a PIM?

PIM is usually caused when two or more signals are used in passive components in conjunction with some non-linear elements. This causes the signals to interfere with each other and create unwanted signals.

For example, when two cables made from different materials are used, this can cause PIM due to the different material make-up of the cables emitting incompatible signals.

Another factor that causes PIM is the environment in which the device is operating from. If the temperature varies wildly, or if thereís lots of polluted air, the metal components might rust. The environment can also cause the metals around the junctions to have a slightly unstable connection. 

How Does PIM Testing Work?

While antennas are the go-to areas for PIM testing, you can conduct a PIM test anywhere you think there might be an issue. As a general rule of thumb, PIM issues often appear when the antenna or equipment is installed. However, they also appear if youíre adding new carriers to outdated antenna systems.

There are two popular types of PIM testing methods that you can conduct to check for any PIM or how your antennaís signal performs.

Reflective or Reverse PIM Testing

In a reflective or reverse PIM test, you emit two signals to the antenna you want to check. From there, you use the port you sent the signals from to capture and measure any PIM that might appear in your antenna.

Though this method is common in the industry, it needs to be conducted with fixed frequencies, as the electrical length of your antenna can affect the results.

Sweeping Test Signals

A sweep test is a PIM testing method where you hold a transmit tone fixed in position while changing the frequency of the second transmit tone. This causes the intermodulation (IM) to sweep across different frequencies.

PIMs are the total sum of all the PIM signals that are created on a line at the IM frequency. This means that the sweep test enables you to test the PIM across a range of frequencies, which allows you to paint a picture of the performance of the PIM in your cellular device or antenna.


Invest in the Right Equipment

For a successful PIM test, you must have the right equipment. Here at TMG, we stock a large collection of PIM testing equipment to suit your needs.

The Kaelus External PIM Finder is a compact and convenient solution that can help you identify and locate external PIM sources, such as loose or corroded metals. It quickly supresses the interfering signal with a variety of methods, including removing or covering the PIM source.

If youíre still not sure how to conduct your own PIM test, get in touch with our experts today. We will help you with all your PIM testing needs and more!

Contact TMG Today

Since our company was first established over thirty years ago, we have been providing cutting-edge testing equipment to the electrical, telecommunications, transport, and utilities industries. Exclusive partnerships with industry-leading brands from around the world allow us to offer our customers the most innovative products available anywhere on the market. To find out more about any of our products or services, contact TMG today by phone or email.


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