FAQs - Handsets and Devices

1 What power do TETRA handsets use and how does this compare with older analogue systems?

2 Do TETRA handsets pulse?

3 How are SARs measured?

4 If TETRA radios are used in cars or on motorbikes is the user exposed to a higher level of RF?

5 What effect does wearing a ear-piece have?

6 What if a TETRA handset is worn on a lapel or on a belt?

7 Can there be audio problems or ‘spiking’ from TETRA handsets?

8 Should covert users, who wear concealed devices on their bodies next to their skin, and sometimes transmit continuously for longer periods, be concerned about RF exposure?

9 Will the use of ElectroDOT on TETRA terminals help mitigate the impact of radio frequency emissions on users?

1 What power do TETRA handsets use and how does this compare with older analogue systems?

If a TETRA radio is awaiting or receiving a call the power is very low. When it is transmitting the power levels are comparable to those of a mobile phone. The typical transmitted power from a portable radio is 1 Watt and this would be reduced to 0.25 watts because 4 handsets share time-slots on a base station, and reduced further when near a base station by adaptive power control.

Adaptive power control adjusts the power output to the lowest level needed to maintain reliable communication with the base station.

These factors mean that TETRA handsets operate with somewhere between 6 and 180 times less power than the analogue radios that preceded the TETRA system.

2 Do TETRA handsets pulse?

TETRA portable radios pulse at 17.65Hz. They operate on a time sharing basis with four sharing one base station transmitter, so each transmits for 14 milliseconds, and is then silent for 42 milliseconds before it transmits again.

However the handsets operate using very low power – with most operating at only 1 Watt or less with the average power being 0.25 watt; they emit RF only while the equipment is in transmit mode, which tends to be for very brief periods; and they use a feature called adaptive power control, which means that the radio continually adjusts its power output to the lowest level needed to maintain communication with the base station.

3 How are SARs measured?

The exposure standard for portable and mobile devices employs a unit of measurement known as the Specific Absorption Rate (SAR) which is measured in Watts per kilogram. The ICNIRP guidelines set a localised exposure limit for occupational use of 10 Watts per kilogram, averaged over 10 grams of body tissue. SAR measurements are generally calculated in a laboratory using a ‘phantom’ head or body which contains material of a similar density to that which would be found within the human body, and using probes to measure the level and distance that the heat penetrates.

Whilst there may be differences between the SAR levels of various devices, and variations depending on the way they are used and how they are carried or worn, all the products supplied by members of the TETRA Industry Group comply with the ICNIRP guidelines for radio frequency exposure.

4 If TETRA radios are used in cars or on motorbikes is the user exposed to a higher level of RF?

Measurements have shown that if multiple occupants in vehicles all have TETRA handsets people experience the greatest exposure from their own handset because the power drops very rapidly with distance. It is advisable not to stand within a few centimetres of a vehicle mounted ariel for a period of time as in this circumstance exposure limits could be exceeded.

Measurements done on motorcycles using a 3 watt antenna showed that if the antenna is more than 10cm away from the rider’s body, which is usually the arrangement, the exposure is not an issue. When the antenna was moved to within a few centimetres of the rider’s back during the study, measurements of around 0.5w per Kg over 10g of body tissue were obtained. This is well within the exposure guidelines.

For more information on vehicle SAR measurements, look at Dr Phil Chadwick’s presentation in the 2007 section of our Events page.

5 What effect does wearing a ear-piece have?

The exposure to RF from a TETRA handset is below guidelines in all points of the head when a handset is used, and less than that if an earpiece is used. There is a possibility that is a cable from an earpiece runs along a cheek the exposure can be greater than with a handset alone, but again, always within the limits set by the guidelines.

6 What if a TETRA handset is worn on a lapel or on a belt?

SAR measures were conducted by Dr Phil Chadwick using ‘phantoms’ with the TETRA handset worn on belts and lapels, with and without anti-stab vests. The localised results were 0.4 watt per Kg when worn on a belt, and 0.2watt per Kg when worn on the lapel, both well within the exposure guidelines. The wearing of anti-stab vests reduced the exposure slightly when the radio was worn at the belt, probably as they move the antenna of the handset slightly away from the body, but did not affect the SAR when worn at the lapel.

7 Can there be audio problems or ‘spiking’ from TETRA handsets?

Some people experience a well known phenomenon called ‘microwave hearing’ at high intensities. In the early days of TETRA handsets there were adjustment issues and unpleasant spikes of noise were heard by some users. This must have been annoying but unlikely to cause a health effect.

8 Should covert users, who wear concealed devices on their bodies next to their skin, and sometimes transmit continuously for longer periods, be concerned about RF exposure?

No, laboratory testing has been carried out using various configurations of body-worn equipment using a body phantom. The results have demonstrated that exposure remains within occupational ICNIRP guidelines wherever the equipment is worn. There is no cumulative RF exposure effect from longer transmissions.

9 Will the use of ElectroDOT on TETRA terminals help mitigate the impact of radio frequency emissions on users?

From time to time a number of different products come onto the market making various claims about providing protection against radio-frequency or electrical emissions.

All the terminals and equipment manufactured and supplied by members of the TETRA Industry Group comply with international guidelines that are fully supported by robust and rigorous scientific research and endorsed by the World Health Organisation (WHO). The members of the group do not therefore endorse the use of ElectroDOT or similar products.

ElectroDOT claims to combat 'electro-pollution' by adjusting the 'vibes' or emissions from electrical equipment. To the best of our knowledge there has been no independent scientific or health study to review these claims. Expert advice suggests that the alleged health effects that the product seeks to negate are not recognised by science and that the way the device operates does not seem to be based on the laws of physics.