This EMF calculator provides a simplified, theoretical calculation based on far-field plane wave approximations.
Here's a breakdown of its accuracy and limitations:
How Accurate is this Calculator?
That's an excellent and crucial question! Understanding the accuracy and limitations of any calculator like this is vital for proper interpretation of its results, especially when dealing with safety.
First Look" or Screening Tool:
This calculator is highly accurate for providing a "first look" or screening assessment of potential EMF exposure in the far-field region (further away from the antenna).
Regulatory bodies like Ofcom (in the UK) and organizations like the RSGB (Radio Society of Great Britain) explicitly endorse and use similar simplified calculators (often based on the ITU-T K.52 method) as a valid method for amateur radio operators to demonstrate compliance with ICNIRP guidelines (Source 1.2, 1.3).
Far-Field Approximations:
The core of this calculator's physics relies on far-field approximations. In the far-field, the electromagnetic waves behave like "plane waves" – the electric (E) and magnetic (H) fields are perpendicular to each other, in phase, and have a constant ratio (377 Ohms in free space). This allows for straightforward calculations of power density (S) from EIRP and distance using the inverse square law (Source 2.2, 2.5).
The calculated "Separation Distance" and "Horizontal Distance" are derived from these far-field power density limits.
ICNIRP Guidelines:
The calculator uses the public exposure reference levels from ICNIRP 1998 and 2020 guidelines. These are established by independent scientific commissions (Source 3.4) and are the basis for regulations in many countries. Compliance with these "reference levels" generally ensures compliance with the underlying "basic restrictions" (which relate to actual energy absorption in the body). However, exceeding a reference level doesn't automatically mean basic restrictions are exceeded, but it does trigger the need for further, more detailed assessment (Source 3.5).
Key Limitations and Scenarios Where Accuracy Decreases:
Near-Field Region:
This is the biggest limitation. Close to the antenna (the "near-field" region, typically within a few wavelengths), the electromagnetic fields are complex and reactive. The E and H fields are not necessarily in phase, their relationship is not a simple 377 Ohms, and field strengths decrease much more rapidly (e.g., inverse cube or higher power, not inverse square) (Source 2.1, 2.2, 4.2).
The calculator's results are less accurate in the near-field. The "Reactive Nearfield Distance" displayed is a simplified approximation, and actual field patterns and hot spots can be highly variable and dependent on the specific antenna geometry (Source 2.2).
Many amateur radio compliance boundaries often fall within the near-field or transition regions (Source 2.2).
Environmental Factors:
The calculator assumes free-space propagation. It does not account for: Reflections: From buildings, ground, vehicles, or other conductive surfaces, which can create standing waves and localized "hot spots" of higher field strength. Obstructions/Absorption: Walls, trees, terrain, etc., which can attenuate (reduce) or scatter the fields.
Multi-path propagation:
Signals arriving via multiple paths.
Multiple Transmitters:
If multiple antennas are transmitting simultaneously, their fields combine in complex ways. This calculator assesses a single source. For multiple sources, aggregate EMF calculations are typically required (Source 1.2).
Antenna Type and Pattern:
While it takes gain into account, the calculator assumes an ideal isotropic or dipole radiation pattern in the far-field. Real antenna patterns are complex and vary with direction and elevation. The "worst-case" compliance distance calculated by such tools is often conservative (Source 1.5).
Measurement vs. Calculation:
Accurate EMF measurements in the field are technically challenging and require expensive, specialized calibrated equipment. Errors in EMF measurement can be significant (e.g., 1 dB in far-field, 3-6 dB in near-field) (Source 4.1). This highlights that even physical measurements have their own accuracy challenges.
Conclusion:
This calculator is a valuable and accepted tool for initial compliance assessment and understanding general exposure levels in the far-field for amateur radio. It provides a good estimate to determine if further, more detailed assessment (such as professional modeling or specialized measurements) is needed.
It is explicitly stated in the disclaimer (and supported by external sources) that this is a simplified tool and should not be considered a definitive, highly precise measurement for all real-world, complex scenarios, especially in the near-field or where multiple reflections are present.