I am putting a 40m antenna in my attic and I was wondering would it be safe to have a shack in the room right below the attic (10ft of coax or less) or should I have my shack in the basement/ground level (50ft coax).

Are there any health effects of sitting to close to the antenna. I am planning to operate max 100w on HF and 50w on VHF/UHF.

  • $\begingroup$ See Phil Frost W8II's spot-on answer here. There are 12 separate links there, the majority pointing to scientific research. $\endgroup$ Apr 13, 2019 at 14:34
  • $\begingroup$ Just a somewhat related sidenote: Unlike USA, within Europe, rules based on transmitter output power are not considered to be acceptable. Instead, there are blanket rules, which allow use up to certain EIRP, and above that, calculations of safe distance need to be done. $\endgroup$
    – AndrejaKo
    Apr 20, 2019 at 16:51

2 Answers 2


Various organizations have issued guidelines on maximum permissible exposure. Below a certain power, the station can be assumed harmless. Above that power, some more careful design is prudent. Your station is mostly below that threshold, except possibly on the upper HF bands.

Thresholds below which a station does not need to be evaluated, according to the ARRL:

  • 40 meters and lower frequencies: 500 watts
  • 30 meters: 425 watts
  • 20 meters: 225 watts
  • 17 meters: 125 watts
  • 15 meters: 100 watts
  • 12 meters: 75 watts
  • 10 meters, and all VHF: 50 watts
  • 70 cm: 70 watts
  • 33 cm: 150 watts
  • 23 cm: 200 watts
  • all higher frequencies: 250 watts

The lower thresholds around VHF are due to the increased energy absorption of human tissue at those frequencies. The cornea is especially at risk because it's small and has no blood flow to cool it.

As you say you intend to operate 100 watts on HF, and 50 watts on VHF, you are below these thresholds except on 12 and 10 meters. So if you want to be safe, reduce power a little bit on these bands and there should be no issue at all having the shack near the antenna.

  • $\begingroup$ Thanks for the reply Phil. 12 and 10m are not something that holds my interest. I will start with 40m and gradually expand to 80m and 20m bands. On VHF and UHF I rarely use more than 10w and I can't recall when I needed 50w (probably never) so I should be fine. $\endgroup$ Apr 18, 2019 at 5:06

The FCC regulates RF exposure for safety and health. RF exposure must be evaluated on a station-by-station basis. As a free public service, the American Radio Relay League (ARRL) makes available a free download of RF Exposure and You by staff member Ed Hare, W1RFI. Chapter 5 contains the references needed to complete the RF Exposure Station Evaluation and Exemption Worksheets. The League has published numerous works over the years, including some that can help you interact with neighbors on the subject, if needed.


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