Tag Archives: RF Exposure

Ohio Section Journal – The Technical Coordinator – January 2022 edition

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.

Once my article is published in the Journal, I will also make it available on my site with a link to the published edition.

You can receive the Journal and other Ohio Section news by joining the mailing list Tom has setup. You do not need to be a member of the ARRL, Ohio Section, or even a ham to join the mailing list. Please sign up!

If you are an ARRL member and reside in the Ohio Section, update your mailing preferences to receive Ohio Section news in your inbox. Those residing outside the section will need to use the mailing list link above.
Updating your ARRL profile will deliver news from the section where you reside (if the leadership chooses to use this method).
Go to www.arrl.org and logon.
Click Edit your Profile.
You will be taken to the Edit Your Profile page. On the first tab Edit Info, verify your Email address is correct.
Click the Edit Email Subscriptions tab.
Check the News and information from your Division Director and Section Manager box.
Click Save.

Now without further ado…


Read the full edition at:

THE TECHNICAL COORDINATOR
Jeff Kopcak – TC
k8jtk@arrl.net

Hey gang,

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.

N8EI’s RF Exposure Assessment Tool

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.

VHF/UHF:

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
ARRL RF Exposure Calculator

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.

“Hoot” – WB8VUL

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.

Tom – W8TAB (Busch Funeral)

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.

Ohio Section Journal – The Technical Coordinator – May 2021 edition

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.

Once my article is published in the Journal, I will also make it available on my site with a link to the published edition.

You can receive the Journal and other Ohio Section news by joining the mailing list Tom has setup. You do not need to be a member of the ARRL, Ohio Section, or even a ham to join the mailing list. Please sign up!

If you are an ARRL member and reside in the Ohio Section, update your mailing preferences to receive Ohio Section news in your inbox. Those residing outside the section will need to use the mailing list link above.
Updating your ARRL profile will deliver news from the section where you reside (if the leadership chooses to use this method).
Go to www.arrl.org and logon.
Click Edit your Profile.
You will be taken to the Edit Your Profile page. On the first tab Edit Info, verify your Email address is correct.
Click the Edit Email Subscriptions tab.
Check the News and information from your Division Director and Section Manager box.
Click Save.

Now without further ado…


Read the full edition at:

THE TECHNICAL COORDINATOR
Jeff Kopcak – TC
k8jtk@arrl.net

DSCF5081 K8JTKHey gang,

The new FCC exposure requirements. Maybe you’ve heard about them. Maybe not. Maybe wondering how they apply to your station. The FCC Report and Order does not change RF Exposure (RFE) limits but does require all services, including amateur radio, to evaluate limits or take the exemption. There’s probably a lot I don’t understand. With respect to those much smarter than myself, I’ll try my best to explain this but I’m probably going to get some stuff wrong. In addition to covering reasons for these changes and what they mean to most hams, I’ll walk through an exception calculation. Those are easiest and likely the only calculation a ham might need to perform in most cases.

In 2019, the FCC adopted new rules to limit human exposure to radio frequency energy. These rules went into effect on May 3rd, 2021. Not much changed in these new rules except that Amateur Radio is no longer categorically excluded from performing these evaluations to demonstrate compliance. Previously, only when a station exceeded certain power limits was an evaluation required. For the most part, operating barefoot on HF (without an amplifier, typically 100 watts or less) or operating most dual band radios with 50 watts or less, all were categorically exempt. The second exclusion, no mobile stations had to perform these evaluations. Both exclusions are now removed, gone. Exclusions are replaced with the exemption.

Removing the amateur radio exclusions means hams are now required to perform evaluations in all cases. But! You do not submit anything to the FCC. Do the evaluation, print out/save results or put notes on paper – they are to be kept with each station’s records. These records would be used in a situation where a complaint is filed with the FCC against your station. Such as: neighbor doesn’t care for your tower/antenna. Writes the FCC saying their family is subject to harmful radiation. The FCC takes those complains fairly seriously and will come knocking for an inspection (which they can – and will do. See 97.103, (a) and (c) specifically). The representative may ask for this evaluation. They will implicitly trust the results if they appear to be correct and the station is otherwise compliant. This is the self-regulation abilities we are allotted by the FCC. The FCC will inform the neighbor, based on evaluation of the station, it was found to be compliant and they have nothing to worry about. Another scenario maybe a building permit is sought in order to erect a tower. The entity that grants the permit might ask to have an evaluation completed.

In any case, each amateur station certifies, on their 605 form, they will comply with Radiofrequency Radiation Safety. Licensed hams are considered trained in safety by way of passing the license exam. Completing an RF safety evaluation does not exempt any station from being otherwise compliant and responsible. If a station is transmitting, someone comes up and touches the antenna, the station operating the equipment is still responsible.

If you were one that completed an evaluation under the old rules, that evaluation is still valid until 2023. You have 2 years to complete an evaluation under the new rules. Every station (not grandfathered under the old rules) must complete an evaluation after May 3, 2021 – including new stations or when any significant changes are made to an existing. Changes would include an increase in power, better antenna, better coax, moving the antenna closer to areas occupied by humans. HTs manufactured before May 3, 2021 are grandfathered – no evaluation needed ever. HTs manufactured after May 3, a SAR (Specific Absorption Rate) evaluation is performed by the manufacturer.

The exemption calculation is a formula which indicates if the antenna is compliant or more evaluation is needed. Exemptions require less calculations than a full exposure analysis. Exemptions cannot be taken with in the reactive nearfield. Distance to a person is important. Any transmitter within 20 cm (7.87 inches) of the body is considered in the nearfield and requires a SAR evaluation. Nearfield also varies with frequency.

The HT falls into this weird area because they are almost always used within 7.87 inches of the body. At this time, the methods for completing an evaluation are not clear for a few reasons: 1) above 300 MHz is not really measurable, which only affects 2-meter handhelds. 2) SAR evaluations are very costly and require specially calibrated equipment. 3) absorption inside the body is very hard to measure. Cell phone manufactures have to complete SAR evaluations for every handset and antenna configuration. To add insult-to-injury, a SAR would have to be completed in each position of the radio. That is to say holding the radio straight up, slight angle, talking across the microphone, holding the radio with the right hand, left hand, and so on. Cha-ching! Not so fast. Radio manufactures will be responsible for performing this SAR evaluation. In the evaluation, they will likely use the stock rubber duck antenna provided with the radio. If you change the antenna (as most of us do) with a 3rd party or aftermarket, that means all evaluations need to be performed using the new configuration. This is an area the ARRL is still working out with the FCC for clarification. Right now, your HT is OK. Will manufacturers pass on the cost to the consumer? Unknown for sure but very likely.

MPE chart (hamradioschool.com)

Don’t forget these evaluations need to be performed at field day sites, repeater sites, and beacon locations. Field day sites may need restrictions placed on frequency or power allowed to meet the requirements. Adjustments to antennas maybe needed, adding time to the field day setup.

In places where SAR is performed, an MPE (Maximum Permissible Exposure) chart displays the amount of energy which should not be exceeded at different frequencies. There are two different categories: occupational/controlled exposure (hams and their families) at 6-minute average and general population/uncontrolled (everyone else, such as neighbors) with a 30-minute average. MPE is lowest between 30 MHz and 300 MHz because those frequencies are easily absorbed by the human body.

Say we have a station with a multiband antenna (20-10 meters) with 0 dbd of gain (manufacturer specs). There is a sidewalk 15 feet (5 meters) away (closest human exposure to radiation) from the antenna. The transmitter outputs 100 watts into 50 feet of RG-58. The highest frequency in operation is 29.70 MHz. 50 feet of RG-58 at 29.7 MHz is rated at 1db of loss (mfr specs), which is 22% (find a gain/loss table or calculator for this percentage).

First, are people within the distances (antenna to human) in the table below for near field exposure?

Nearest person would be 15 feet away and lowest band we plan to operate is the 20-meter band since the antenna is capable. No, humans are not within the reactive nearfield (10.3 feet). We can continue with the exemption calculation. If humans are within the nearfield, a full evaluation needs to be completed.

Next, calculate the maximum ERP. For a multiband antenna, ERP decreases at higher frequencies so you only need to calculate at the highest frequency the station plans to use. 10 meters in this case.

3450 R2/f2 = Maximum ERP (formula for the range 1.34-30 MHz)

3450 x (5 meters)2 / (29.7 MHz)2 = 97.8 watts maximum ERP

Calculate the station’s ERP:

(Transmitter power – Feedline loss) x Antenna gain = ERP

(100W – 22W) x 1.0 = 78 Watts ERP

To compare, 78 watts is less than 97.8 watts. This antenna qualifies for an exception!

What happens if the station cannot take the exception? If you never transmit 29.7 MHz and only plan to use lower frequencies, calculate at the lower frequency. Move the antenna further away from the sidewalk. Or perform a full evaluation. The exemption numbers are verrry conservative numbers and conservatively safe. If actual exposure is calculated on the sidewalk, it will be less than the exception calculation. Averaging time is not taken into account. If the station talks for 15 minutes and listens for another 15 minutes, the exposure is halved. Areas like a sidewalk, people are likely to be there for only a few seconds at a time.

Online calculators are a huge help in performing power density estimations. VP9KF’s calculator performs MPE calculations. The Lake Washington Ham Club site calculates MPE by taking into account transmitter duty cycle. It will provide minimum safe distance to the antenna.

To perform a full analysis, the FCC aid for evaluating human exposure is OET Bulletin 65 and OET Bulletin 65 supplement B. The no-longer-in-print book by Ed Hare – W1RFI is available for download as a PDF. Modeling software is available for free or little cost. One such modeling application is EZNEC. The ARRL is working on finding or developing tools for all hams to use. Those can be found at: http://www.arrl.org/rf-exposure and the ARRL Technical Information Service is a member benefit that can provide more information. Finally, Greg – N9GL, Chairman of the ARRL RF Safety committee, gave a very informative presentation on these changes. It runs 2 hours with Q&A. Ria – N2RJ, director of the ARRL Hudson Division, has a YouTube channel with a video on this topic. The majority of the information in this article came from both videos, thanks to both Greg and Ria.

FCC Radio Frequency Exposure Rules from Dan Marler on Vimeo.

Recent FCC NPRM’s have put ham radio use of the 5GHz band at risk. These frequencies are utilized for things like mesh networking. Who wants to take away these allocations? Commercial interests to push the 5G mobile standard. These same interests have already taken part of the 3 GHz WiFi band. ARDEN Mesh is fighting back, legally, against repurposing these allocations. If you have 5 GHz AREDN mesh nodes in the lower 45 – 5.850-5.895 GHz or upper 30 – 5.895-5.925 GHz channels, please take the time to read and respond to their solicitation for information.

Another huge thank you to the West Chester Amateur Radio Association – WC8VOA, which I’m also a member, for having me as the presenter at their May 6th meeting. West Chester is a suburb of Cincinnati and I’m in a suburb of Cleveland so this meeting was all virtual. The presentation was on ham radio VoIP modes (Voice over IP) and my system that links these modes together. There was great questions and discussion around VoIP. This is the club that operates out of the Voice of America Museum and holds tours during Hamvention. You can find their Monday night net on my system at 8pm.

That’s about it for this month. Thanks for reading and 73… de Jeff – K8JTK