Electrical – HDMI Cable interfering with mobile phone network


Just had a "spectrum engineering officer" from OFCOM (the UK's communications regulator) visit our office investigating alleged interference from our building with a local cell phone tower. After waving an aerial attached to what looked like a portable spectrum analyser around he decided that the HDMI cable feeding a set of four TVs was causing the problem.

This seems extremely unlikely to everyone in our office and we are wondering of their is any validity in his claim. We are a ground floor office in a modern concrete building and the phone tower is on the the opposite side of the street on the top of a multi-story car park (about 4 stories high).

Is it possible for a leaky HDMI to cause such interference?

(He did assure us that we haven't broken any regulations and that no action would be taken.)

Best Answer

Ok, first of all, that wasn't an OFCOM official, probably, in all likelihood. Best case, you just failed some security penetration testing.

Other than that, if the guy with the directive antenna, proper spectrum analyzer and training says "that's where the radiation comes from", I'd trust him.

HDMI symbol rates are, depending on HDMI generation used, 165, 340 or 600 MHz, meaning that at these frequencies or typically odd multiples thereof, you'll see harmonics, with power strongly decaying with the multiple.

UK uses cellular bands at 800, 900, 1400 and 1800, 2100, 2300 and 2600 MHz; aside from the unlikely 600 MHz·3 interference, those are not likely victims.

Then again, OFCOM does have a phone number for spectrum interference investigation: 020 7981 3131 (option 2); so ask them whether someone was dispatched to your location. It's a legitimate concern.