One of the responsibilities of the Technical Coordinator in the Ohio Section is to submit something for the Section Journal. The Section Journal covers Amateur Radio related things happening in and around the ARRL Ohio Section. It is published by the Section Manager Tom – WB8LCD and articles are submitted by cabinet members.
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Now without further ado…
Read the full edition at:
THE TECHNICAL COORDINATOR
Jeff Kopcak – TC
New FCC RF exposure requirements went into effect May 3, 2021. Have you performed your station evaluation? There is much confusion and speculation around these requirements. Clarifications are still being sought as a good number of things remain unclear. Continuing research, observing presentations, and working with others have cleared up many concepts for me, while others remain clear as mud.
Since my article last May, everything there is still applicable: every ham needs to complete an assessment, the exposure rules haven’t changed, hams are no longer categorically excluded from these calculations, nothing is submitted to the FCC. Calculations only need to be available when a station inspection is performed. Handy talkies manufactured before May 2021 are all grandfathered. All of the calculation tools found online are still valid and applicable. Use the tool or method most applicable to your situation or knowledge.
One thing that’s been expressed, I’ve heard it through the Technical Specialists, is confusion on calculations or what exactly needs to be completed. Our Technical Specialists are asked for support. Jason – N8EI presented to his club, SARA, on adhering to the FCC exposure rules. Get in touch with Jason or I can forward the request if you’re interested in having such a presentation for your group.
In my previous article, I presented an exception calculation. While still valid, it is a lot more effort than most need to complete. Take the ARRL’s RF Exposure Calculator. It is a much simpler tool to complete an assessment. Returned numbers are very conservative estimates. Meaning they err heavily on the side of safety when compared to actual measured results. The minimum safe distance to an antenna maybe calculated at 40 ft. A full assessment might determine safe distance to be 33 ft. Don’t assume ‘I’m fine’ without evidence to back it up.
Jason, in addition to his presentation, put together a simple step-by-step walk-through of the calculations. His assessment includes radio information, determining feed line loss, antenna gain, and duty cycles. Each step features a description and links to common information such as typical feed line loss for different types of coax. Available on his project site and on GitHub for learning, validating the code, fixing issues, including any new and relevant parameters, or customize for your site.
One should assume “worst-case” when using these calculators. Ever talked for 30 minutes in a single transmission on FM? Highly unusual, but none-the-less, that is worst-case. Those outliers should be factored in these calculations.
Consider an HF station:
1. Station transmits on many different frequencies. Highest frequency is the upper part of 10 meters (29.700 MHz). The radio can do, at most, 100 watts connected to a 3 dBi gain horizontal antenna (both manufacturer specs). While transmitting in the FM portion (100% duty cycle), the operator yaps for 30 minutes then listens for 10 minutes before repeating the cycle.
Pretty rough to have someone talking for 30 minutes straight in a single key-down let-alone using full power at 100% duty. Assume full output power reaches the antenna. These are not real-world, but again, fit a worst-case scenario. For controlled environment, minimum safe distance from a human to the station’s antenna is 6.5 feet, uncontrolled is 14.6 feet. If the antenna is more than 14.6 feet in the air, like on a 50 ft tower, that station’s configuration is compliant. Print the results and include them with station records. This station’s evaluation is done.
Unless right next to your house, neighbors’ deck, a sidewalk, or other public area where the antenna is within the 14.6 ft minimum safe distance to the closest human, no additional work here is needed.
2. Same configuration, changing to SSB (20%) reduces the minimum safe distance to 2.9 ft controlled and 6.5 ft uncontrolled.
Minimum safe distance numbers are reduced with a reduction in duty cycle, frequency, gain, or power.
3. Changing the frequency from example #1 to the low end of 80m, 3.5 MHz, using AM (still 100% duty cycle). Minimum safe distances are 0.8 ft controlled and 1.7 ft uncontrolled.
This is an example showing how only a realistic change in frequency reduces the minimum safe distance to the same antenna.
4. Using a 50-watt mobile radio on 146.520 MHz, the 2m national simplex calling frequency (FM, 100% duty cycle, 30/10 talk time, 3 dBi gain) is 4.7 ft controlled and 10.5 ft uncontrolled minimum safe distances.
5. Using a 50-watt mobile radio on 446.000 MHz, the 440 national simplex calling frequency (FM, 100% duty cycle, 30/10 talk time, 3 dBi gain) is 3.8 ft controlled and 8.6 ft uncontrolled minimum safe distances.
However, there is a catch with this last one. While these numbers are good safety guidelines, absorption by the human body is not measurable above 300 MHz. Results above that don’t mean much.
Remember uncontrolled is everyone in the general public and neighbors. Controlled is for hams, their families, and those who work with RF as an occupation.
Most stations with antennas in the air are going to be fine with the results from these tools. However, if the antenna is closer to the ground, in the house, or configured for NVIS, additional work would be needed. Not sure if people maybe within acceptable distances? Use a piece of string or rope to determine this. If anyone would be within 15 ft (rounded up, from the first example) while in operation, remediation suggestions are:
- use or calculate lower frequencies if higher frequencies are not used
- use or calculate lower duty cycles
- use or calculate lower power
- observe shorter transmit times
- perform a full station evaluation to obtain a more realistic minimum safe distance or use antenna modeling applications such as EZNEC
- rope-off or otherwise isolate the antenna, keeping people away from the structure
- re-position the antenna in a better configuration/move further away from the environment
- not use it when people will be around or near the antenna
- point the elements in a different direction from the dwelling
- move antenna further away from vehicle passengers
What’s still not entirely clear with these requirements? Gain rating on many antennas, namely verticals, has been discouraged as it is hard to prove based on the mounting and radial systems. Gain is not published for many antennas. Now needed as part of calculations, hams are between a rock and a hard-place not having that information.
Absorption calculations of HTs are fairly complicated and responsibility of the manufacturer. It is unknown, though, what needs to be completed if the radio is modified, such as using a 3rd party aftermarket antenna.
There remains some confusion if “minimum safe distance” is from the center/feed point of the antenna or any part of the antenna. Those who have previously worked with these calculations indicate it is any radiating part of the antenna structure.
The ARRL has updated their RF Exposure page with more links and resources. Ed Hare – W1RFI wrote an article for the September 2021 edition of QST. He describes how to determine exception status and how to use the ARRL’s new RF Exposure calculator. Ed is the author of the out-of-print book but available as a PDF, RF Exposure and You.
Remember, evaluations (exceptions or calculations) need to be performed by May 3, 2023. New stations or ones with significant changes (power output, antenna type, operating on a new band, operating with a new mode) all require an assessment be completed before operating.
Earlier this month, the FCC announced the winning bidders from its 5G spectrum auction of the 3.45 GHz band. The auction, which was structured to be “diverse” and have competition front of mind, was the highest grossing auction in the FCC’s history at $22.5 trillion. The entire allocation for ham radio wasn’t lost (yet) as 3.3 – 3.5 GHz was the ham radio allocation with 3.45-3.5 GHz being the subject of the auction. Even though the spectrum was used mostly by AREDN mesh, hams didn’t have much of a justification for that spectrum. We don’t stand a chance as a group of hobbyists against $22.5 trillion as part of a money grab in the name of “competition.” Use it or lose it. We kinda used it and still lost it. Please consider supporting the ARRL Spectrum Defense Fund and projects that are justifying use of our spectrum.
Over the holidays, we lost two hams that were close to me and very active in the amateur radio community. William G. “Hoot” Gibson – WB8VUL was a long-standing member of the Wood County Amateur Radio Club. He held many positions in the club, was always participating in actives and promoting the club. Being a BGSU grad, he was always asking me about the university and how school was going. I would ask him how they used to do things and he would talk about history, which I always found fascinating. I enjoyed his stories and advice.
Thomas A. Bishop – W8TAB was in a long-time battle with cancer. In our last E-mail exchange, he was not doing well and trying to manage. Tom was an alum of Westlake High School, as am I. He was fortunate enough to be part of the ham radio club which, unfortunately, was long gone by the time I roamed the halls. We were both in broadcasting and loved technology. He always had time to chat.
Both will be greatly missed.
Thanks for reading and 73… de Jeff – K8JTK
CORRECTION since publication: I incorrectly stated the 3.45 GHz band spectrum auction amount. It should have been $22.5 billion, not trillion. An update is included in next month’s article.