Posted by: GW7AAV | February 8, 2010

TETRA – Tin hats and trunchions

There has for some time been a complete load of rubbish talked about TETRA (TErrestrial Trunked RAdio) called Airwave in the UK and now according to various sources, including the Daily Express police forces in the UK are facing compensation claims from officers over radios they say make them ill and have been blamed by the family of one officer for his death from cancer.

In a test case due to be heard shortly five Lancashire police officers are claiming that their radios made them ill. Hopefully common sense will prevail and they will shown to either swinging the lead or at least the reasons for there illness have nothing to do with the radios, because it is we the tax payers who will pick up the tab and we have already paid out thousands of pounds to these people in sick pay.

The bull about TETRA has been bubbling along for a few years and is based on some misinformation that is repeated in the Daily Express article, namely that the system works on a frequency of its 17.6 hertz signal, which is close to 16Hz at which causes the brain to loose calcium.

TETRA actually usually works in the UHF bands between 330 and 950MHz, but could be configured for almost any band. In the UK the new emergency services TETRA radios use 380 – 385 MHz (mobile) and 390 – 395 MHz (fixed). A very similar frequency spectrum that there old analogue radios worked on if fact.

So where does the low frequency of 17.6 hertz come from? To quote Wikipedia

The downlink (i.e. the output of the base station) is normally a continuous transmission consisting of either specific communications with mobile(s), synchronisation or other general broadcasts. All slots are usually filled with a burst even if idle (continuous mode). Although the system uses 18 frames per second only 17 of these are used for traffic channels, with the 18th frame reserved for signalling, Short Data Service messages (like SMS in GSM) or synchronisation. The frame structure in TETRA (17.65 frames per second = 18 frames in 1.02 seconds), consists of 18000 symbols/s / 255 symbols/slot / 4 slots/frame, and is the cause of the perceived “amplitude modulation” at 17 Hz and is especially apparent in mobiles/portables which only transmit on one slot/4. They use the remaining three slots to switch frequency to receive a burst from the base station two slots later and then return to their transmit frequency.

So the 17.6 hertz that these people are worrying about is the modulation of a signal that is a millions miles away from the danger zone. The AM signal at 17.6 hertz is not actually there, it is only perceived, that is the signal sounds like AM. The digital modulation takes place inside the radio and is done before the signal is amplified and therefore if there is any radiation at 17.6 hertz it is at so low a level it would be unlikely to penetrate the case of the transceiver never mind some dumb coppers thick skull. If there was a danger zone it would be right next to the antenna on a high powered base station and not from PC Plod’s walkie talkie.

Maybe the applicants in these lawsuits will be asked to prove they never used a cell-phone or operated a micro-wave oven, which are far more likely to cause harm. Next time you see a policeman ask if you can see his helmet and find out if it is lined with tin foil. On second thoughts don’t. Oh! If you fancy a laugh try Googling TETRA and mind control. Where’s that tin foil?

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