# Cell phone tower radiation safe distance calculator

Updated on December 24, 2016

Cell phone tower radiation safety distance calculation

Cell phone tower radiation-The subject has become a bone of contention after the categorization of non –ionizing radiation emitted by cell phones and cell towers as possible carcinogenic agents by WHO .No result has drawn any definite conclusion since all results are based on short term exposure periods and more results are also needed for long term exposure periods to get some better understanding of this issue. Hence ,a prudent use of cell phones is the necessity of hour.

Let us have some information on cell towers before calculating the safety distance from cell tower.

Generally there are two types :

1.GBT(Ground Based Towers which are erected on the earth)

2. RTT/RTPT(Roof Top Towers/Roof Top Pole Towers which are erected on

the terrace of the buildings)

BTS: Base Transceiver Station or simply Base Station in mobile network is the first interface node which assists radio communication between the network and the user equipment and also responsible for the EMF radiation.

Sector/Cell: Physical coverage area of mobile network.

Each cell tower will normally have 3 sectors, but not all the towers and it depends on the coverage requirement.

EIRP Calculation formula

Equivalent /Effective Isotropic Radiated Power is the total amount of power radiated by sector(isotropic) antennas after deducting the loss of connecting waveguide.(All sector antennas have isotropic radiating pattern. That is, radiation power will be even in all direction)

EIRP=Total output power of TRX carrier(coming out of BTS Duplexer)- Loss of waveguide +Antenna gain

( Total output power of TRX carrier in dBm, Loss of waveguide in dB and sector antenna gain in dBi)

Federal Communications Commission (FCC) guidelines on cell tower EMF exposure limits.

Limits for General Public/Uncontrolled Exposure

Frequency Range(Mhz)
Power Density(W/square metre)
300-1500
f*/150
1500-100000
10

International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines on cell tower EMF exposure limits.

Limits for General Public/Uncontrolled Exposure

Frequency Range(Mhz)
Power Density(W/square metre)
400-2000
f*/200
2000-300000
10

*- operating or base channel frequency in Mhz.

Calculation of horizontal safety distance is explained in the following example.

A 40 metre GBT tower is working with GSM,CDMA,UMTS(W-CDMA) & WiMAX mobile services and its details are given below.

Technical Details

Base station type
GSM
CDMA
W-CDMA
WiMAX
Number of sectors
3
3
3
3
Base channel/operating frequency(Mhz)
Sector1 949.2
Sector1 871.26
Sector1 2156.2
Sector1 2637.5

Sector2 950
Sector2 871.26
Sector2 2156.2
Sector2 2637.5

Sector3 948.6
Sector3 871.26
Sector3 2156.2
Sector3 2637.5
Number of carriers /sector
4/4/4
2/2/2
1/1/1
1/1/1
Antenna make
Agisson
Mobi
Mobi
Laird
Antenna gain(dBi)
17
18
18
16
TRX carrier output power(dBm)
46
43
46
43
Combiner loss
3
0
0
0
RF Waveguide length(from BTS to antenna)
60
45
50
0*
RF cable unit loss/100metre(dB)
4
4
4
0
DTX(Discontinuous transmission) factor
0.9
1
1
1
ATPC(Automatic Transmit Power Control) factor
0.9
1
1
1

*- In some BTS systems,TRX carriers unit(RRU-Remote Radio Unit) will be installed very close to antenna .In such cases, RF cable length from RRU to antenna will be less than a metre and hence RF cable loss can be omitted.

EIRP for GSM system

For BCCH( Broadcast Control Channel) Channel

=(46-3)-(60*0.04)+17

=57.6dBm

=575.439watts

For other carriers=EIRP(BCCH)*(0.9*0.9)*(N-1)

N-Total number of carriers

=575.439*0.81*(4-1)

=1398.31

Total EIRP=1973.58 watts/sector-------equation 1

EIRP for CDMA system

For Pilot channel =43-(45*0.04)+18

=59.2dBm

=831.7637watts

Total EIRP=EIRP(Pilot channel)+(N-1)*EIRP(Pilot channel)

=1663.5275watts/sector--------equation 2

EIRP for UMTS system

For Pilot channel=46-(50*0.04)+18

=62dBm

Total EIRP =1584.893watts/sector---------equation 3

EIRP for WiMAX system

For Base channel= 43+16

= 59 dBm

Total EIRP = 794.328watts/sector---------equation 4

(If Azimuths of all sectors with horizontal radiation pattern of antennas and the residential building are known, we can calculate the number of cell sectors causing the EMF exposure or simply use 2 which is the worst case EMF scenario due to that particular cell tower.)

Let us assume a building with 2 floors is located near the tower and azimuth of the building with respect to the tower is 110degree .In the worst case scenario, the building will receive the EMF exposure from 2 sectors .(120 degree(or)90 degree horizontal beam width sector antennas are mostly used by mobile service operators and we have taken 120 degree sector antenna for calculation purpose)

Case-I

1st sector 2nd sector 3rd sector

Azimuth 0 degree 120 degree 240 degree

Case-II

1st sector 2nd sector 3rd sector

Azimuth 60 degree 180 degree 300 degree

Case-III

1st sector 2nd sector 3rd sector

Azimuth 60 degree 160 degree 300 degree

(See the photo capsule )

In the first case, the building will receive the exposure from 2nd sector.

In the second case, the building will receive the exposure from 1st sector.

In the third case, the EMF exposure will have an overlapping horizontal radiation pattern and hence the building will receive the exposure from both 1st and 2nd sectors.(In our example also, we have included the EMF exposure from 2 sectors of RF cell sources for calculating the horizontal safety distance from RF emitter of cell sites)

According to Free Space Propagation loss

S=P/4πD^2

P- Total EMF power (watts)

S-EMF power density(watts/metre^2)

Using the above formula,

S limit=EIRP total/4πD^2

Horizontal safe distance D from the RF emitter=SQRT((EIRP)1/4πS1+(EIRP)2/4πS2+……..(EIRP)n/4πSn)

n= Number of Radio Frequency sources.

In our example,number of RF sources are four.(GSM,CDMA,UMTS &WiMAX etc)

D=SQRT((EIRP)gsm total/4πS limit(gsm)+(EIRP)cdma total/4πS limit(cdma)+(EIRP)w-cdma total/4πS limit(w-cdma)+(EIRP)wimax total/4πS limit(wimax))

EIRP gsm total

In worst case scenario, the building mentioned above will receive an EMF exposure from the two sectors.

From equation 1

EIRP gsm total=( EIRP for GSM system/sector)*2

=1973.758*2

=3947.516watts.

EIRP cdma total

From equation 2

EIRP cdma total=( EIRP for CDMA system/sector)*2

=1663.5275*2

=3327.055watts.

EIRP umts( w-cdma) total

From equation 3

EIRP umts total=( EIRP for UMTS(W-CDMA) system/sector)*2

=1584.893*2

=3169.786watts.

EIRP wimax total

From equation 4

EIRP wimax total=( EIRP for WiMAX system/sector)*2

=794.328*2

=1588.656watts.

S limit under FCC guidelines

S limit for GSM system=f/150

=949.2/150(The building may receive the exposure

from 1st & 2nd sectors and hence the lowest working

frequency(BCCH) is taken among the two sectors.)

=6.328 watts/metre^2

S limit for CDMA system=f/150

=871.26/150

=5.8084 watts/metre^2

S limit for W-CDMA system=10 watts/metre^2

S limit for WiMAX system =10 watts/metre^2

(frequency of operation is more than 1500 Mhz)

S limit under ICNIRP guidelines

S limit for GSM system=f/200

=949.2/200(The building may receive the exposure from 1st & 2nd sectors and hence the lowest working frequency(BCCH) is taken among the two sectors.)

=4.746 watts/metre^2

S limit for CDMA system=f/200

=871.26/200

=4.3563 watts/metre^2

S limit for W-CDMA system=10 watts/metre^2

S limit for WiMAX system =10 watts/metre^2

(frequency of operation is more than 2000 Mhz)

FCC horizontal safe distance from the RF emitter

=SQRT((3947.516/4π*6.328)+(3327.055/4π*5.8084)+(3169.789/4π*10)+(1588.656/4π*10))

=SQRT(133.106)

=11.537metre

ICNIRP horizontal safe distance from the RF emitter

=SQRT((3947.516/4π*4.746)+(3327.055/4π*4.3563)+(3169.789/4π*10)+(1588.656/4π*10))

=SQRT(164.831)

=12.838metre

In worst case scenario,

FCC horizontal safe distance =11.537metre

ICNIRP horizontal safe distance=12.838metre

FAQs

1.Horizontal safe distance from a 40m GBT tower is 13m and the height of its antenna is 37m from the ground. A building with a height of 8m is observed near the tower which (see the figure)is 11metre away. Will the building fall under the hazardous zone area /whether the building will receive an EMF exposure more than that of the recommended limit?

No ,obviously the building is not coming under the main radiating lobe of the antenna since the effective height of the antenna is 29metre.(after deducting the building height )

(See the photo capsule)

2. Based on the theoretical calculation, if a residential building falls under the hazardous zone area /if we suspect the residential building seems to be receiving the EMF exposure more than that of the recommended level, what will we do?

All cell sites should be EMF compliant. That is, all network operators should get EMF compliance certificate and NOC(No Objection Certificate) from the respective regulating authority before the roll out of their services. If you are suspecting about the EMF exposure level of the tower, you can approach the network operator for verifying the EMF compliance report of the tower. If the network operator is not responding to you/if you are still doubtful about the EMF report, you can measure the EMF level yourself using a good quality EMF power density meter to get the real life radiation level and contact the regulating authority of your country(DoT for India and FCC for the USA etc) to raise your concern /you can directly approach the regulating authority to lodge the complaint. If your case is genuine, they will inspect the site and do the real time EMF measurement and recommend the following RF modifications to the network operator to make the cell site EMF compliant.

1. Reducing the TRX carrier output power.

2.Increasing the height of the radiating antenna.

3.Changing the azimuth of the radiating antenna etc.

If the tower is not made to be EMF compliant despite the above modifications, then it will be dismantled /relocated.

3.Is it correct to go for the EMF shield, if our residential building comes under the hazardous/non- EMF compliant zone?

It is not prudent to go for EMF shielding to protect our residence from cell tower radiation. Let me tell the whys and the wherefores.

1. Shielding the whole surrounding environment like garden, veranda and other open spaces is a daunting task.

2. Functioning of the EMF shielding devices and its trustworthiness need to be ascertained periodically.

3. Finally, under the EMF shielding environment almost 90% of your mobile signal will get attenuated and hence your mobile phones will be put into the upper radiating power level by Base Transceiver Stations of especially mobile technologies with tight power control algorithm like CDMA,W-CDMA and LTE etc which will aggravate the EMF exposure from cell phone(increasing SAR level) due to the very close proximity of your body to the mobile phone even if you are using a good quality phone with low SAR value. So, it is advisable to bring your building to be out of the hazardous/non-EMF compliant zone rather than going for EMF shielding.

Stay healthy and Happy living.

(Original content with Safety Distance Calculator is available on my personal blog subtleplace.blogspot.in )

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