Hazards and device to map BTS radiation zones

How microwaves are hazardous to humans

Thermal effects (main, well-established):

• Water molecules in tissue rotate with the field; the energy becomes heat (dielectric heating).
• Organs with poor blood flow cannot remove heat: eyes (cataract) and testes (temporary sterility) are most sensitive.
• Whole-body heating raises body temperature, causing heat stress, fatigue and burns at high levels.
• Penetration depth falls with frequency: at 2.45 GHz a few cm, above 10 GHz mostly skin heating.
• Human body resonance (about 70–100 MHz for an adult) gives the highest whole-body absorption.

Non-thermal effects (studied, less certain): headaches, sleep disturbance, changes in nervous and cardiovascular response, and possible genetic effects. IARC (WHO) classes RF fields as "possibly carcinogenic to humans" (Group 2B).

Other hazards: sparks and ignition of fuel (HERF), triggering of electro-explosive devices (HERO), and interference with pacemakers and medical implants.

Device to map radiation zones around a GSM BTS

The usual instrument is a broadband isotropic RF field meter (EMF/radiation hazard meter) with a probe; for frequency-selective mapping a calibrated antenna + spectrum analyzer is used.

Broadband isotropic probe meter: working principle

  3 orthogonal      diode/thermocouple    meter unit
  dipoles (x,y,z)   detectors + filter    (√sum, display)
     |                  |                     |
  [ Ex Ey Ez ] ---> [ DC ∝ E² ] ---> [ E = √(Ex²+Ey²+Ez²) ]
                                       → V/m, W/m², % limit

1. The probe has three mutually perpendicular small dipoles (for E) or loops (for H), so the reading does not depend on polarisation or direction (isotropic).
2. Each element feeds a diode detector (fast, sensitive) or thermocouple (true rms). Resistive leads carry the DC to the meter without picking up RF.
3. The meter adds the three squared components: E² = Ex² + Ey² + Ez², and shows E (V/m), power density S = E²/377 (W/m²), or % of the ICNIRP limit. Readings are averaged over 6 minutes.

Frequency-selective method: a calibrated log-periodic/biconical antenna and spectrum analyzer measure GSM 900 and 1800 carriers separately; E = received level + antenna factor + cable loss.

Mapping procedure:

1. Measure on a grid of points around the tower at several heights (e.g. 1.1, 1.5, 1.7 m) and in the main beam direction.
2. Record the BTS power and traffic; scale to maximum power.
3. Compare each reading with the limits (public at 900 MHz: 4.5 W/m², 41 V/m; at 1800 MHz: 9 W/m², 58 V/m; ICNIRP 1998).
4. Plot contours: exclusion (occupational) zone, public compliance boundary, and safe zone.

GSM 900: λ = 33.3 cm; GSM 1800: λ = 16.7 cm. For a 2 m panel antenna at 900 MHz, the far field begins about 2D²/λ = 24 m away.