Tetra / Airwave

Once upon a time, your friendly neighbourhood scoundrel would be able to listen to unencrypted Police communications using a handheld radio scanner.

These days most Police forces use the encrypted Airwave/Tetra radio system.

Tetra in the UK uses the 400MHz band and will typically have three antennas emitting 20W each. Defenders of the Tetra system point out that’s less energy than the light bulbs in your lounge emit, but I wonder how many Chief Constables or MPs would be happy to have a ‘Tetra Chandelier’ in their family home?

Also, a lot of information on the Internet states that Tetra ‘pulses’ at frequencies that may have biological effects on humans – who pulse @ 16 Hertz. In fact, the Stewart Report of 2000 recommended avoiding frequencies that were subsequently used.

Here are two photos of our own Optoelectronics Digital Scout detecting Tetra in my own property. The reading was taken in one of the hotter spots, before I did some shielding. A cheap £10 bug detector – which is supposed to have a range of just a few feet – even detected the Tetra signal at this spot. Remember this reading is at 500m from the mast, through several brick walls. In fact, I’ve seen it go as high as -29 dBm.

Image of Optoelectronics Digital Scout showing Tetra incoming.

Each 3.0 dBm increment on the photo on the right equals a doubling of received power & a typical not-too-near-a-mast signal level would be -48.0 dBm.

Last summer I took the meter to the Hack Green Nuclear Bunker in Sandbach to see what reading you’d get in that kind of RF-free environment. In the basement of Hack Green, where you can get no mobile phone signal, it only drops to -51.0 dBm.


Medcross Group Tetra report

Powerwatch Tetra page

Wikipedia Tetra entry

Telegraph story on Police Tetra mast from 2004

2010 Update – Lancashire police were the first force in the country to pilot Tetra back in 2001.  The report below, from the Telegraph,  states that the local branch of the Police Federation have logged 176 complaints about Tetra.



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