Category Archives: Emergency Communication

RF Exposure Calculations for Emergency Commmunication

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I’ve calculated some safe distances for RF exposure in typical emergency communication situations. These are for a 5 W HT (handheld radio) or a 50 W mobile, on 2 m and 70 cm, each with typical antennas. The results may also be useful for other VHF/UHF portable activities, like ARRL Field Day, Summits on the Air, or Jamboree on the Air.

Very short version: The 6-7 foot social distance we’ve learned to keep is safe for a typical fixed or mobile em-comm deployment. This is the distance between any part of the antenna, including the radials, and a member of the general population. 5 W HTs are safe for handheld use.

The FCC introduced new RF exposure rules for amateur radio in 2021. Hams used to have special exemptions, now we need to do RF exposure evaluations for all uses. If your transmitter and antenna are like the setup used for these calculations, you might be able to use these results. If yours are significantly different, this should help you get started.

Rf safety sign

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Windshield Survey: A COVID-Friendly Emergency Service Project (E. Prep. 7a)

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Emergency Preparedness Merit Badge requirement 7a is “Take part in an emergency service project, either a real one or a practice drill, with a Scouting unit or a community agency.” How do you do this while Scouting at home?

A standard part of our city emergency drills could be adapted as an emergency service project. In a disaster, our emergency volunteers quickly collect information about damage with a “windshield survey” or “windshield damage assessment”. That information is collected centrally.

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BaoFeng HTs and Spurious Emissons

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The January edition of QST has some disturbing data about dirty transmitters in BaoFeng HTs.

Amateurs are responsible for their transmitters being clean, but most of us don’t have the test equipment to check that. Also, manufacturers must meet the FCC regulations for every transmitter sold.

The ARRL Lab set up at hamfests and tested the HTs that hams had with them. Over four years, only 5% to 9% of BaoFeng HTs passed the test. Alinco, Icom, Kenwood, and Yaesu had 100% pass rates. Wouxon improved from 83% to 100% over the years.

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Plastic Pipe Roof Antenna Support

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I noticed a clever antenna mount on another ham’s roof, so I built one myself. Putting my VHF/UHF antenna at the highest point of the roof has really improved my ability to copy some of the far-flung participants in our weekly ARES/RACES net.

plastic pipe antenna mount close-up

A cradle built from two-inch ABS DWV (drain, waste, and vent) pipe sits across the ridge of the roof. Legs two feet long go down on each side and a two-foot section is a vertical antenna mast.

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Using a Mobile Antenna as a Temporary Base Antenna

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For our July Fourth Safety Watch this year, I used my dual-band mobile antenna on a ground plane mount on a camera tripod. I’d purchased a Nagoya GPK-01 NMO Ground Plane Kit ($28) to test my NMO mobile antenna, because my mag mount seemed flaky.

As I was drifting off to sleep one night, I thought that the 1/4-20 screw on my camera tripod might fit the holes on the ground plane kit. It did, so now I have a robust, free-standing, dual-band antenna for em-comm use.

IMG 4753

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