There are various manufacturers offering TETRA products to meet different customer needs, including hand-held portable radios, those worn on lapels or belts, those designed to be installed in vehicles and personal digital assistants (PDAs).
A TETRA radio device can be used to communicate in a variety of ways including as a two-way radio, via a control room or direct to another user in the same talk group as a phone, and to send and receive data, such as images and short text messages.
A TETRA system uses a network of base stations, which provide radio coverage so as to enable TETRA devices to emit lower power than those of most other conventional professional systems. If a TETRA radio is awaiting or receiving a call the human exposure to radio wave emissions is so low as to be virtually unmeasurable. When transmitting the power level from a portable radio is typically up to 1.8 Watts, and that from the mobile radios installed in vehicles is around 3 Watts. TETRA devices use a feature called Adaptive Power Control, which adjusts the power output to the lowest level needed to maintain reliable communication with the base station.
TETRA devices, like other wireless equipment, are subject to rigorous, science- based safety guidelines, set by independent expert groups like the International Commission on Non-Ionising Radiation Protection (ICNIRP). These guidelines govern human exposure to radio frequency emissions and incorporate substantial safety factors to protect both users and the general public. 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.
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 Health Group comply with the ICNIRP guidelines for radio-frequency exposure.
TETRA devices and pulsing
TETRA portable and mobile devices pulse at 17.65Hz. Concern about pulsed 16Hz radio frequency emissions arose as a result of some inconclusive research dating back to the 1970s. This study suggested that 16Hz emissions affected the movement of calcium, which is important in the human nervous system. The Stewart Inquiry, which reported in May 2000, suggested that “If such effects occur as a result of exposure to mobile phones, their implications for cell function are unclear and no obvious health risk has been suggested. Nevertheless, as a precautionary measure, amplitude modulation around 16 Hz should be avoided, if possible, in future developments in signal coding”.
Since the Stewart report there have been further research studies around the world, including the work of a team at the UK Defence Science and Technology Laboratory, published in the International Journal of Radiation Biology in December 2005. Importantly, none of these studies has found any impact on calcium movement or any other adverse health effects.
Compatibility and Interference
Nearly all electronic devices are susceptible to electromagnetic interference (EMI). When a potential problem is identified, it can usually be managed or remedied.
Laboratory and clinical tests have found that digital wireless phones might interfere under certain conditions with some pacemakers and hearing aids. Often, there are steps users can take to minimise or prevent interference, such as keeping an operating phone six inches (15 cm) from an implanted pacemaker or adopting other measures to accommodate the use of hearing aids. Users should follow the advice provided by the manufacturers of medical equipment.
Unlike some other professional radio communications systems, TETRA devices have a transmit-inhibit function. They can be prevented from transmitting, while the user can still receive communications. This feature is particularly useful in medical environments.
For more information on compatibility and interference, see the section below. Also, the FAQs page of this web site has sections on both handsets and compatibility and interference.