Robert, Explain the FCC Rules to your customer and that while your equipment conforms to the technical requirements, that is not always sufficient to prevent interference in all cases. If their eyes haven't glazed over yet, you might explain the effect of source-to-victim separation distance.
The cellular carrier may well be experiencing an interference level of 20dB or more. But is all of that attributable to your customers equipment? Are there other sources? The carriers are pretty good at locating the loudest/nearest source of interference, but typically do not quantify that interference strength. Fortunately it is not necessary if you can get cooperation from both parties. If so…… Perform an "on-off" test while the cell carrier monitors their Received Signal Strength Indicator in real time. Their RSSI will drop by X dB when your customer's equipment is switched off. X represents the maximum reduction in interference level that could be achieved if your customer's equipment were perfectly quiet. Now you have a best case (dB) number. Any remaining interference is not yours. Temporarily shutting down a customer's equipment for this test can be painful. It really helps if they understand the situation and the FCC Rules. The cellular carrier interference hunters are generally cooperative and helpful. They just want to resolve the issue ASAP. Hope this helps, Bob Sykes From: Moeller, Robert T. [mailto:[email protected]] Sent: Wednesday, September 26, 2018 9:41 AM To: [email protected] Subject: [PSES] Equipment EMI Issue Hello, Maybe someone can help with this question: We have had one of our systems installed and operating at a customer site in the US, and now suddenly a local Cell Ph Company has made complaint that we have an unintentional signal radiating at 780 MHz which is interfering with their Cell Tower. Our equipment is EMC tested to CISPR Class A for business only use, and at 780 Mhz our radiated Level at 3Meters is under the Class A limit of 57 dB at 780 Mhz. Question is, can the complaining company legally demand that we drop the signal further, they may be looking at a necessary reduction of current level by 20 dB lower. 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