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PIM Master - Helps to Speed Network Traffic in Mass Transport System

PIM Master to Help Speed Network Traffic in Mass Transit System

Interference hunter


If you think passive intermodulation (PIM) is a problem on a rooftop, just think how bad it could be in a subway tunnel. That’s the challenge PIM Master helped solve for a company contracted to install radiating cable in the wireless network that will allow travelers to maintain wireless service while traveling in the Austrian mass transit system.

The company needed a test solution that could accurately and quickly locate PIM because radiating cable is sensitive to PIM sources close to the cable. Given the fact these cables are going to be installed in tunnels and subway systems near many other metal objects, there is a better than average chance PIM will rear its ugly head.

 

Interference hunter

A scenario was created in the company’s warehouse to test the PIM performance of the cable, as well as determine Distance-to-PIM (DTP) in the PIM Master. A radiating cable 25 m long was placed on the floor. Initial measurements indicated poor PIM performance, which DTP quickly identified as a defective low PIM termination at the far end of the cable.

After replacing the termination, the PIM was very low. Steel wool was then placed on the outside of the cable at various locations to simulate external PIM sources. The following chart shows how accurately DTP was able to locate the steel wool as it was moved along the cable.

Interference hunter

* The outside of the cable was marked by the manufacturer every 1 m. To determine the theoretical location the electrical distance to the first mark was measured and the distance the steel wool was moved from the first mark was added.

Two pieces of steel wool were placed on the radiating cable, one at 10.47 m and another at 22.47 m, to attempt to confuse DTP with multiple PIM sources. DTP not only saw the two PIM sources but maintained excellent accuracy in identifying their locations.

The results concluded:

  • Radiating cable is sensitive to PIM sources near the cable
  • DTP can accurately locate PIM sources along a radiating cable
  • Average accuracy for locating single and multiple PIM sources was 0.13 m

 

For more information on measuring PIM, a series of technical documents can be found in the library tab on the PIM Master web page.

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