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Cordless (DECT) phone

cordless telefone with base station and handset
Today, most cordless phones are DECT (Digital Enhanced Cordless Telecommunication) systems. These consist of a base station and one or more handsets. While emissions from the handset only occur during a call, those from the base station are normally continuous.
Emissions from the base station and handset are very low. Handset emissions are about 40 times lower than the recommended limit, and base station emissions decline rapidly with distance from the source – to a level about 25 times lower than the recommended limit 20 cm away, and about 100 times lower at a distance of 1 m.
It is not currently known whether electromagnetic fields (EMFs) from DECT phones represent a health risk.
The following advice can be offered to people who, taking a precautionary approach, wish to keep EMFs to a minimum in their home or at work:

  • Ensure that DECT base units are placed at least 50 cm away from relaxation places or work stations occupied for long periods.
  • For longer calls, use a corded phone instead, or use a headset. Remember that some corded phones also operate according to the DECT standard and thus produce emissions.
  • Low radiation DECT telephones are available in specialised shops. There are models where the base station does not emit radiation when the headset is in place and models where the headset reduces radiation if there is a good connection with the base station. More information about this is available in specialised shops or via the following web page:

Detailed information

In recent years, analogue systems such as CT1+ (Cordless Telephone 1+) have been superseded in the marketplace by the DECT standard. The following information mainly relates to DECT phones.

1. Technical data

The base station and the handset, or several handsets, transmit and receive alternately. As the device only produces emissions during transmission, emissions are pulsed (Figure 1).

Range:
up to 300 m
Frequency:
1,88 - 1,9 GHz (high frequency)
Wavelength:
approx. 16 cm

Transmitting power

 
Power base station (mW))
Power handset (mW)
Peak transmitting power
250
250
6 telephone calls
60
10
1 telephone call
10
10
Idle state
2,5
0

Transmission structure
Transmission sequence for a DECT base station and 6 active handsets (6 calls)new window
Transmission sequence for a DECT base station and 6 active handsets (6 calls) Figure 1: Transmission structure
The peak transmitting power of the base station and handset is 250 mW. Averaged over time, however, emissions are lower, since transmission is not continuous. A 10-millisecond frame is divided into 24 time-slots. When a call is in progress, a handset (e.g. the one marked in red in Figure 1) transmits during one of these time slots and receives a signal from the base station (hatched in red) during the time-slot 5 milliseconds later. The base station can communicate with up to six handsets at a time. In the idle state, when no calls are in progress, the base station transmits a brief pulse every 10 milliseconds (bottom of Figure 1). In certain models of telephone, the base station never emits if the handset is in place.
In most models, the emissions from DECT telephone are always of the same strength during a call, irrespective of the distance between base station and handset, and of the quality of the connection. In models that save power, the transmitting power is regulated and their emissions are less strong when the connection is good.

Low-frequency fields from the handset
As the handset only requires power for transmission and reception, the power supply from the battery is turned on and off every 5 milliseconds during a call. This gives rise to a low-frequency magnetic field of 200 Hz.

2. Exposure measurements

Exposure to emissions is best described by the specific absorption rate (SAR, in watts per kilogram), which is a measurement of the electromagnetic radiation (W) absorbed by the human body (kg). In appliances operated at least one wavelength away from the body (16 cm in this case), the electric field can be measured as a basis for calculation of the SAR.
In a study carried out by the IT`IS Foundation on behalf of the FOPH, electric fields were measured for three different DECT base stations and the SAR was determined for four different handsets [1].
Base station: electric fields
The electric fields measured close to a DECT base station, with and without the operation of one or more handsets, are shown in Figure 3. It is striking that these are highly distance dependent. The field strengths measured are always well below the limit of 60 V/m recommended by the ICNIRP [2]. Even while six calls are in progress, the field strength at a distance of 20 cm is 10 times lower than this limit.
In an epidemiological study, 166 persons in the region of Basel carried around a personal dosimeter during one week and exposure to all relevant sources of radiofrequency electromagnetic fields were measured [8]. The results showed that 23% of the overall exposure (0.23 V/m) was due to the base station of the cordless phone. A similar study in France yield comparable results [9].
Electric field over distance for different modes of operation
Figure 3: Electric field (E-field) over distance for different modes of operation [1]. The results are only shown for the base station for which the highest E-field values were measured.

3. Health effects

Base station and handset: short-term effects
Short-term health effects due to electromagnetic fields can be assessed on the basis of the limits recommended by the ICNIRP [2]. As mentioned above, emissions from handsets and base stations are well below these limits. Accordingly, short-term health effects are not to be expected with the use of cordless telephone handsets or base stations.

Handset: long-term effects
The ICNIRP recommendations on limits do not, however, cover possible long-term effects of electromagnetic radiation. Such effects are currently being investigated in a number of epidemiological studies. Although this research is mainly focused on the health effects of mobile phone emissions, several studies also include emissions from cordless phone handsets. In this regard, a German study found no association between cordless phone use – even over a period of more than 5 years – and the occurrence of brain tumours [4]. In contrast, a recent Swedish study concludes that elevated risks of brain tumours are found in particular when cordless phones have been used for many years [5]. The same Swedish research group investigated the association between the use of cordless phones and testicular cancer [10]. They could not find any association. Additional the Interphone study, coordinated by the International Agency for Research on Cancer (IARC) could not give conclusive answers about the possible association between mobile phone emissions and brain tumours. These results would have been relevant for cordless phones as well. Thus, at present, no consensus exists concerning long-term effects of emissions from cordless phone handsets.
The association between unspecific symptoms of ill-health and self-reported sleep disturbances with the use of cordless phones was investigated in epidemiological studies. No consistent association between subjective sleep quality and cordless phone was found [11-13]. Additionally, cordless phone use does not seem to influence the function of the brain blood barrier [14].

Base station: long-term effects
No specific studies are currently being conducted on the long-term effects of cordless phone base stations. With regard to possible health effects of weak high-frequency emissions, such as those that occur with these base stations, the small number of studies available do not yield any firm conclusions. Since 2007, some studies on the relation between subjective well-being and exposure to different radiofrequency electromagnetic fields (including DECT base stations) was investigated [11,15]. No consistent association between exposure and well-being was found.

Interference with implants
According to a German study, neither base stations nor handsets cause interference with pacemakers or defibrillators [6].

4. Legal regulations

As end-user products, cordless phones are subject to the Ordinance on Telecommunication Equipment (FAV). This Ordinance makes reference to technical standards applicable to health protection in the area of electromagnetic fields. These standards, issued by the European Committee for Electrotechnical Standardization (CENELEC), specify methods for measuring emissions from specific appliances. DECT handsets are covered by EN 50371 [7]; no standard is currently available for base stations.

5. Literature

1. Kramer A et al. Development of Procedures for the Assessment of Human Exposure to EMF from Wireless Devices in Home and Office Environments. 2005. IT'IS report. See "Documents"
2. ICNIRP. Guidelines for limiting exposure to time-varying electric, magnetic and electromagnetic fields up to 300 GHz. Health Phys. 75: 494-521. 1998. See "Further information"
3. http://ec.europa.eu/comm/health/ph_determinants/environment/EMF/brochure_en.pdf
4. Schuz J et al. Cellular Phones, Cordless Phones, and the Risks of Glioma and Meningioma (Interphone Study Group, Germany). Am.J Epidemiol. 163: 512-20. 2006
5. Hardell L et al. Pooled analysis of two case-control studies on use of cellular and cordless telephones and the risk for malignant brain tumours diagnosed in 1997-2003. Int Arch.Occup Environ Health. 2006
6. Bahr A et al. Schutz von Personen mit Implantaten und Körperhilfen in elektromagnetischen Feldern des Mobilfunks, UMTS, DECT, Powerline und Induktionsfunkanlagen. 2005. See "Further information"
7. Norm EN 50360: 2001 (Corrigendum 2006). Produktnorm zum Nachweis der Übereinstimmung von Mobiltelefonen mit den Basisgrenzwerten hinsichtlich der Sicherheit von Personen in elektromagnetischen Feldern (300 MHz bis 3 GHz).
8. Frei et al. Temporal and spatial variability of personal exposure to radiofrequency electromagnetic fields. Environ Res. 109(6): 779-85. 2009
9. Viel et al. Radiofrequency exposure in the French general population: band, time, location and activity variability. Environ Int. 35(8):1150-4. 2009
10. Hardell et al. Use of cellular and cordless telephones and risk of testicular cancer.Int J Androl. 30(2):115-22. 2007
11. Mohler et al. Effects of radiofrequency electromagnetic field exposure on self-reported sleep quality: a cross-sectional study. Radiation Res. in press. 2010
12. Redmayne et al. Cordless telephone use: implications for mobile phone research. J Environ Monit. 12(4):809-12. 2010
13. Mortazavi et al. Prevalence of subjective poor health symptoms associated with exposure to electromagnetic fields among university students. Bioelectromagnetics. 28(4):326-30. 2007
14. Söderqvist et al. Mobile and cordless telephones, serum transthyretin and the blood-cerebrospinal fluid barrier: a cross-sectional study. Environ Health. 2009

Specialist staff: emf@bag.admin.ch
Last updated on: 22.07.2010

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