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Notification under BEMFV
If you run a fixed amateur radio station in Germany, you have to show that the limits for electromagnetic fields are met. The BEMFV (German ordinance on the procedure for limiting electromagnetic fields) sets out how. This page explains the process, works out the distances per band and adds up several transmitters, which is the part the simple calculators leave out.
Not legal advice. What's binding is the Verordnung über das Nachweisverfahren zur Begrenzung elektromagnetischer Felder (BEMFV), the 26th ordinance under the Bundes-Immissionsschutzgesetz (26. BImSchV, German emission limits) and whatever the Bundesnetzagentur (BNetzA, German regulator) asks for in its forms. The calculation here is a far-field estimate: it helps with planning and understanding, it replaces neither the prescribed procedure nor a measurement.
Your station
One row per combination of band, antenna and mode. If you use a wire antenna on 20 m and a Yagi on 2 m, enter two rows.
| Band | Frequency (MHz) | Power at the antenna feed (W) | Gain (dBi) | Mode | EIRP (average) | Distance alone |
|---|
Overall assessment
Several transmitters add up. What matters is the sum of their shares of the respective limits: each one can be below its limit and the sum still above.
What the limits mean
The values apply to the general public, meaning everyone who has nothing to do with your station: neighbours, family, passers-by.
Limits under the 26. BImSchV, values for the general public. Calculated in the far field, without reflections, using free-space loss. Close to the antenna, behind walls and over conductive ground you get different values, usually worse ones.
Who has to notify what?
The obligation depends on radiated power. Fixed amateur stations that reach or exceed an equivalent isotropic radiated power (EIRP) of 10 watts must be notified to the Bundesnetzagentur. Below that it's enough to stay within the limits, but you still have to be able to prove it if asked.
Ten watts EIRP comes quickly: ten watts into an antenna with 6 dBi gain is already around 40 watts EIRP. The “EIRP" column in the table above tells you where you stand.
What goes into the notification
- The notification itself on the Bundesnetzagentur form, with callsign and location of the station.
- A data sheet per transmitting installation: frequency range, power, antenna type, gain, mounting height, main beam direction.
- Proof of field strength, by calculation or measurement. The Bundesnetzagentur provides a procedure for the calculation; the estimate here follows the same idea but isn't the same form.
- A site sketch, showing where the relevant area where people spend time is and how far it is from the antenna.
- Details on mode and transmit time, because both feed into the assessment via the duty cycle.
You keep the documents and show them on request; the notification itself goes to the Bundesnetzagentur. The current forms and the procedure are at the Bundesnetzagentur (German), the text of the ordinance at gesetze-im-internet.de.
How the distances come about
Transmit power and antenna gain give the equivalent radiated power. From that, the electric field strength at distance r is E = √(30 · PEIRP) / r. Solved for r, that gives the distance beyond which the limit is met.
Two things often get lost. First the duty cycle: the assessment uses the average over six minutes, not peak power. SSB voice is around 40 per cent, CW about 50, FT8 and FM are continuous carrier. Second the summation: several transmitters or several bands add up proportionally, each share relative to its own limit.
And a warning no formula takes off your hands: the calculation only holds in the far field. At 145 MHz that starts roughly half a metre out, at 3.5 MHz only from about fourteen metres. If you're closer to the antenna than that, this formula gives you no reliable number; only the prescribed procedure or a measurement helps there.
What saves the distance in practice
Height. A few metres more distance upwards works just as well as sideways, and height is easier to come by than land. Next comes the main beam direction: a Yagi that doesn't point at the neighbour's house radiates less towards it by its front-to-back ratio. Only after that comes less power.