Annunciation of a stationary amateur radio system with an EIRP > 10 W in Germany (Anzeige ortsfester Amateurfunkanlagen (BEMFV))

  • Yes,
    The requirement has existed in Germany for over 2 decades.
    Create station description with all requirements.
    Send a table with the data to the RegTP. Station descriptions with all calculation bases and antenna radiation diagrams must be available, but will only be sent to RegTP upon request.

    I´ve done the "Selbsterklärung" 20 years ago, using the programm "Watt32" which includes all forms. no problems.

    Forms are available here:

    73 de Robert

  • DD4YR

    Thanks Robert, but I'm aware about the standard process which has to be send to the BNetzA (former RegTP).

    I should have been more precise with focus on QO-100 operation.

    Has anyone experience in calculating or measuring the field strength according the radiation pattern of a satellite dish? I flipped through the "Wattwächter" (former Watt32) antenna files and couldn't find anything comparable.

    73 de Matthias, DF6LO

  • DF6LO: In the latest „Watt32“-package that I downloaded from the DARC website there is a program called „BEMFV Dish“, written by DL9KCE. In this software you can calculate the so called „Leistungsflussdichte“ for antennas such as parabolic dishes.

    In most cases the value is way below any critical values. Not the EIRP is important for our cases but a value in Watt per square meter (antenna area). As our antennas point upwards into the sky, even the main radiation is well above people or animals, even if they are fairly close to the antenna.

    Best regards

    Holger ‚Geri‘, DK8KW

  • I have asked ARRL for advice, since the requirement also exists in the USA, and received a detailed analysis with lots, lots of data. I have suggested that ARRL make an article of the info provided by this specialist (I think this will be interesting to many).

    I can't make the analysis itself available right now - need to wait for the publication.

    I was interested in actual risk because of my plans to be active with JOTA, when the setup is seen and used by many scouts (children). Due diligence dictates that if an exposure question would come, I would need to have an answer ready.

    My question was on 20W output (PE1CMO kit), 80cm dish, 100% efficiency (50-60% is more likely in practice) and POTY patch antenna. A few comments:

    • One needs to distinguish between near-field and far-field effects. The near-fields are not as serious, because while the dish acts like a spot beam on distance, that isn't true on close distance, the field is lower, so safer.
    • FCC rules make a distinction between amateur exposure and public exposure. Public exposure, 10W/m^2 would be safe for a distance bigger than 7.8 meters.
      Amateur exposure (50W/m^2) would be safe at 3.5m.
      This would be true if the whole body is exposed, for partial exposure (arm in dish) the limits are 40W/m^2 (public) and 200W/m^2 (amateur). The field calculated never goes above 160W/m^2 so it would be entirely safe.
    • Outside the beam the field is 20dB lower, making that field a non-issue
    • The main concern would be someone from the public placing their hand in front of the patch antenna itself. The exposure level is lower than the amateur limit, but above the limit for the public.

    There are much, much more details in the analysis of Ric K5UJU and my comments above really don't do it justice (and I hope my summary is correct!), but I would like ARRL to have the privilege of publication.

    Something to ponder is that geometry dictates that even if the dish is on the ground, the beam would be 2m up at a distance of 4m, at least in the Netherlands (our inclination is roughly 30 degrees). And, given that humans are shorter than 2m, the 4m clearance area doesn't need to be bigger than that.

    So, for my JOTA work, if I clear 4m in front of the dish then there really is no risk of exposure.

    I apologise for being unable to make the detailed analysis available at this point.

  • Hello all,

    I agree with what pe1hzg said regarding the possible zone of exposition to radiation. In Germany we have the principle that I have to protect people outside of the „Controllable Range“, which is basically my own property.

    I submitted this sketch as a part of my documentation for the authorities. In order to save a new submission in the future I entered 75 Watt (minus a few dB for cable/plug losses) in my documentation. 75 Watt PEP is the maximum allowed power for class A. currently I only use 750 mW ... :)

    Vy 73

    Holger ‚Geri‘, DK8KW

  • Hi all,

    Thank you very much for yor useful information. A possibly ARRL publication would be indeed quite helpful.

    DK8KW: Your sketch of the antenna setup and the so called controllable range or space is very helpful too. Actually that is right what I am looking for. Thank you very much for that. Thank you too for the info about Watt32. I first thought that Wattwächter was the successor of Watt32.

    Probably the figures of your calculation have to be modified because you stated to take the maximum allowed PEP of 75 W (- 2 dB = 47.3 W) into account but calculated with ERP. An antenna surface area of 2.8 m² (1.9 m diameter dish) leads at 12.5 cm wavelength to approximately 31 dBi antenna gain, assuming 60 % efficiency. 47.3 W at the feed of the antenna will cause an ERP of 60 kW! At a quite low distance of about 10 x Lambda = 1.25 m (far field assumption?) you will have a power flux density of round about S = 3000 W/m² (26 W/m² in 13.4 m).

    It looks a bit more harmless for my 55 cm dish (21 dBi) and 10 W PEP at the feed. 64 W/m² at 1.25 m.

    Your 750 mW - 2 dB will cause 600 W ERP and 30 W/m² at 1.25 m distance from the dish. So everything is harmless as well.

    I hope I didn't miscalculate in a hurry, so please rectify if necessary.

    73 de Matt, DF6LO

  • I think PEP is the correct method - not ERP.

    ERP is the equivalent output compared to an isotropic radiator. The power into the antenna never gets to be more than the PEP and the total power in the beam from the antenna can never get to be bigger than the PEP assuming the beam is the same width as the dish.

    I probably didn't explain that very well....

    With a 1m dish the area is 0.78m^2 so assuming a perfect dish the power is going to be the PEP/0.78 W per m^2

  • M0VKK: Sorry to say but I fear that is not right. The calculation must take into account the directivity or gain of the antenna.


    It's in German but the equations are universal and one can find this in the standard technical literature as well.

    r = safe distance

    C = attenuation for an specific angle with respect to the main beam direction

    Eg = safe limit of the electric field strength

  • It depends if the area which is uncontrolled is within the beam direction or not. For us, one would need to provide the polar diagram of the transmit antenna and derive its effective gain in the direction to the uncontrolled area. There the gain will be much lower than in the main lobe and possible even less than 0dBi. So yes, you have to give EIRP, but not with the boresight antenna gain, but with the correct one in terms of direction of interest.

  • DH2VA: "... derive its effective gain in the direction to the uncontrolled area."

    That is what C stands for. But one need to know this for the specific antenna in use.

    So the calculation to prove that the field strength at the border of the so called controlled area is within the limit is quite complex. Especially when you take the variety of offset and prime focus dishes into accout. I'm quite sure that there is no real hazard but I wonder if anyone has already shown this in a comprehensible way.

  • I think I got it ...

    (screen shots with courtesy of Thilo, DL9KCE)

    The experimental tool BEMFVDish.exe from DL9KCE (DARC website for member) verifies that the liniear calculation for the power flux density (PFD) assuming a far field situation can be applied even for smaller distances (under certain limits). Taking the exposure limit of 61 V/m into account lead to the following results.

    DK8KW: 1.9 m dish, G=31.4 dBi, PEP=47,3 W

    => safe distance of 23 m (with respect to the center of the main lobe)

    DF6LO: 0.55 m dish, G=20.6 dBi, PEP=10 W

    => safe distance of 3 m (with respect to the center of the main lobe)

    DL9KCE's tool shows an estimation for the beginning of the far field (r0 = 2D²/lambda ("normierter Abstand"), D=diameter of antenna). You can find this as well for instance here .

    Interesting to see is, that the bigger the dish and the higher the frequency, the larger the distance to the beginning of the far field region. Even more interesting that the maximum PFD (Smax) is higher for a smaller dish and lower power. See the oscillating PFD in the near field region.

    DK8KW: Far field starts at r0 = 56 m with PFD=1.66 W/m² (center of main lobe)

    -> level exaltation of about 41 at 0.1xr0=5.3 m

    => Smax=70 W/m² (not fully clear where)

    DF6LO: far field starts at r0 = 4.7 m with PFD=0.44 W/m² (center of main lobe)

    -> level exaltation of about 41 at 0.1xr0=0.44 m

    => Smax=175 W/m² (not fully clear where)

    My earlier assumption regarding the beginning of the far field region with r0 = 10xlambda = 1.25 m is not correct for a parabolic dish. So for DK8KW's setup the 60 kW EIRP is correct but not the PFD with S=3000 W/m² at 1.25 m.

    So actually you can't use the far field formulas but when you look at the diagram (BEMFVDish on the right) you notice that at 0.2 x r0 the deviation is very small. But for distances below that, one has to consider the near field and transition zone.

    Now at the end one have to consider the height of the antenna and the elevation of the main beam of 28.5° (for central Germany, see the sketch in post from DK8KW). I guess we can neglect the side lobes. Regarding the beam width I was too lazy to use the formulas but looked for online calculators.…-beamwidth-calculator.htm


    1.9 m dish, 2.4 GHz, efficiency 0.6, 31.4 dBi

    -3 db +/-2.39°

    -6 dB +/-3.39°

    0.55 m dish, 2.4 GHz, efficiency 0.6, 20.6 dBi

    -3 dB +/-8.27°

    -6 dB +/-11.7°

    -6 dB reduces the safe distance to half the value calculated for the center of the main lobe (see above).

    DK8KW: 23 m/2 = 11.5 m

    DF6LO: 3 m/2 = 1.5 m

    A little bit of trigonometry lead to ...

    DK8KW: Antenna height 2 m, -6 dB at (28.5°-3.39° = 25.11°) elevation

    => at a horizontal distance of 10.4 m the exposure limit is reached at a height of 6.9 m = (2 + 4.9) m

    DF6LO: Antenna height 1.5 m, -6 dB at (28.5°-11.7° = 16.8°) elevation

    => at a horizontal distance of 1.44 m the exposure limit is reached at a height of 1.93 m = (1.5 + 0.43) m

    ... or with respect to the center of the main lobe...

    => at a horizontal distance of 2.64 m the exposure limit is reached at a height of 2.93 m = (1.5 + 1.43) m

    So everything is safe with respect to DK8KW's and my contollable areas.

    DK8KW's setup with 750 mW -2 dB = 473 mW doesn't exeed the exposure limit at all.

    I wonder if the results of the current so called experimental tool BEMFVDish.exe will be accepted by the BNetzA.

  • DF6LO, thanks, Matthias, for your extensive calculations and considerations.

    I wonder if the results of the current so called experimental tool BEMFVDish.exe will be accepted by the BNetzA.

    Well, we shall see! I submitted my sketches and some of the calculations to the BNetzA and didn't get any feedback yet.

    Best 73

    Holger 'Geri', DK8KW