# Impact of keying-up in yagi beam 1.5m (or 5ft) away on 2m FM?

Asking for a friend, of course, this homebrew yagi is probably somewhere between 3 and 6dB gain (not yet analysed) and was aimed about +30 degrees off-center, tilted 10-20 degrees upwards, transmitting 50W on 2m. 'They' were standing side-on, approx. 1.5m away. The over lasted around 1 minute.

I've seen the RF radiation recommendations, which average out the power to at least 6 minutes. If this is the case then the ERP of 100-200W would be much reduced. 'They' would have been standing within the safe-zones, however.

Their eye on the antenna side may also be feeling a dull pain, but that could be psychosomatic :)

Interesting question, my gut feeling tells me that the "dull pain in eye" experienced may not be from RF radiation... but that would be a "gut feeling".

Exposure to RF radiation, and safety of RF radiation is very well documented by the FCC. Realizing that this is US based, and may or may not be applicable for other regions of the world.

The FCC FAQ can be found here: https://www.fcc.gov/engineering-technology/electromagnetic-compatibility-division/radio-frequency-safety/faq/rf-safety

The bullitin with formula's to calculate is the OET65, which can be found here: https://www.fcc.gov/general/oet-bulletins-line#65

Particular interesting is the example of document https://www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet65/oet65.pdf

Page 26 of the pdf-document (numbered as Page 21), lists an example of a 100MHz transmission at 10kW ERP power, experienced by someone standing 20 meters from the antenna-mast.

You can use this to calculate with your own numbers.

Another nice example would be the graph of "FIGURE-1 Power Density vs. Distance (assumes no surface reflection)" on Page 28 of the pdf (numbered as page 24). Which could be use for preliminary estimations of exposure

Furthermore, regulating bodies in various countries would have similar publications, it would be worthwhile checking this at your own discretion.

HTH.

• Thanks for posting those. Ran a quick calculation, which may be incorrect in terms of units used or assumptions, but S = ERP/(4pi(150x150)) should give power density in mW/cm2, if ERP is given in mW. So I plug in the worst case scenario (200W directly, no loss and max gain) and get 0.7mW/cm2. May 6 '16 at 11:26
• Ran into 5 minute edit window. The comment continued: The safe limit, for 30-300Mhz, is 1mW/cm2 in this case (145Mhz), but that's averaged over 6 minutes, much longer than the 1 minute over discussed here. In other words, it appears to be safe in the worst case, by FCC standards, but it's still not clear :) May 6 '16 at 11:33
• Can you specify what it is you are asking when you say "still not clear" ? -- please specify what research you have done in regards to this ? thanks. May 9 '16 at 7:39
• Research? None, that's the point. It's a back of napkin calculation that doesn't take into account where the recipient was standing (inside the safe limit), the particulars of the as-yet untested antenna and the directionality of a Yagi-Uda. However, given that we plugged in the worst case scenario as best we could and found that we're well within safe levels for the general assumptions made by the formula, I think it's only fair to approve your answer. It was an interesting exercise also, so many thanks for that too. May 11 '16 at 9:02