Hintlink - RF Exposure Calculator Help

RF Exposure Calculator Help
This page was last changed on: 2021-09-02 While this re-write is under way this page will reload every 5 minutes.
There are, what could be considered to be, major changes coming in RF Exposure regulations in both the USA (FCC) and UK (Ofcom).
There may also be some in certain countries of the EU using ICNIRP 1998 Guidelines.
v2.0 and greater denotes the use of new FCC compliant calculator (2021).

Regulator	Country	Comments close by	Published	Implementation	New calculator written here?	Help
FCC	USA	Closed	2020-04-01 and 2020-04-06	2021-05-03¹		This page
Ofcom	UK	Closed	2021-03-01	2021-05-18²	Possibly³	UK Help page Ofcom uses ICNIRP 2020 guidelines
Some EU†	Some EU†	n/a	n/a	unknown		EU Help page. Potential change from existing ICNIRP 1998 to ICNIRP 2020 guidelines

Notes: 1. To be performed from 2021-05-03 (new or changed station) or 2023-05-03 (existing station, unchanged). Read 2021-04-02 FCC Public Notice [PDF].
The OMB approved these on 2021-03-01 but only for a period of 3 years.
THIS IS NOW VALID - Published in the FEDERAL REGISTER 2021-04-20
2. Ofcom were required by law to make final consideration on 'published' rules/method of introduction. "We will publish our decision no later than 18 May 2021."
Variations to licences (of all types) were made after that decision was published. Further clarification by Ofcom is on this page.
3. Ofcom (v1.0) and RSGB (v0.1.2-rsgb11a) have spreadsheet calculators, based on Microsoft Excel using .xlsx format. These versions have been tested by me using LibreOffice (v7.1.6 / 7.2.2.2) and found to be usable.
To prevent platform and version limitations, it would be better if calculations were performed online with (browser accessed) server-based code.

† Binding: Cyprus, Czech Republic, Estonia, Finland, France, Hungary, Ireland, Malta, Portugal, Romania, Spain, Germany and Slovakia [13]
Not binding: Austria, Denmark, Latvia, the Netherlands, Sweden, Slovenia (United Kingdom was non-binding but now ex-EU and will use new Ofcom regulations). [6]
Stricter: Belgium, Bulgaria, Croatia, Greece, Italy, Lithuania, Luxemburg and Poland.[8]

RF Exposure Calculator (RFEC) has been around for a while now [since 2006]. This help page finally addresses some of the details required, background and other information.

Scope - FCC
The RF Radiation Evaluation discussed from here and down is only mandated by the FCC for US-based transmitters (inc. radio amateurs in full).
It may be used by you personally to gain an overview of your exposure if you are in another country.
Other countries may adopt the FCC guidance, in which case it may apply to you, albeit with modified levels (check!).

History Current Software Release: v2.2 ( 2021-05-07 ). Current Help Release: v2.2.5 ( 2021-05-21 )
Help release follows code release, e.g. v2.1 code, v2.1.11 help. Help is modified more often than code.

1985-10-08	FCC OET Bulletin 65.
1996-08-01	FCC Report and Order, 96-326
1997-08-27	FCC Second Memorandum Opinion and Order and Notice of Proposed Rule Making, ET Docket 93-62
1997-08-10	FCC OET Bulletin 65 Edition 97-01.
1997-10-18	FCC OET Bulletin 65B Edition 97-01.
2007-10-21	v0.1 beta release.
2012-02-04	v1.0 release. First user proven release.
2013-03-29	FCC 2013 RF Order and Notice - (changes) terminated.
2015-08-18	v1.2 release. Minor interface changes.
2018-12-07	This help page added in draft form.
2019-06-12	This help page expanded and updated.
2019-12-04	FCC Second Report and Order - exemption vs. evaluation.
2021-04-12	FCC OET Bulletin 65 (21-01?), pending re-write by FCC OET/ARRL.
2021-04-12	FCC OET Bulletin 65 Supplement B (21-01?) for Radio Amateurs, pending re-write by FCC OET/ARRL.
2021-04-14	This help page starts catch up with latest (pending) updates.
2021-04-20	OMB approval for Second Report and Order finally published in Federal Register - final approval.
2021-05-03	FCC changes license regulations.
2021-05-03	New calculator v2 released. Help greatly updated.
2021-05-07	v2.1 & 2.2 released. Minor feedback tweaks from users.

What this means
For most amateurs, the major difference is the removal of the categorical exclusion for amateur radio, which means that station owners must determine if
they either qualify for an exemption or must perform a routine environmental evaluation

The main FCC points are:

1. Any exemptions from the RF evaluation requirement, identifying broad criteria that apply to single and multiple RF sources based on power, distance and frequency, irrespective of service classifications.
2. The calculation or measurement methodologies that should be used, in cases where no exemption applies, to determine potential RF exposure levels in the RF evaluation
process.
3. Post-evaluation mitigation procedures, like access, signage and training, to ensure that persons - both the general public and trained personnel - are not
exposed to RF emissions in excess of the established exposure limits. [For amateurs, household residents are classed as 'trained personnel' and accept higher levels of exposure]

Specifically, they create four broad classes of RF exemptions:

1. Extremely low-power devices that transmit at no more than 1 mW [0 dBm].
2. Somewhat higher-power devices, with transmitting antennas that operate within 0.5 to 40 cm of the body,
using a formula based primarily on the localized specific absorption rate (SAR) limits from 100 kHz to 6 GHz. This is primarily aimed at cell (mobile) 'phones and medical devices.
3. Internal electric field shall be used to evaluate the environmental impact of human exposure to radiofrequency (RF) radiation within the frequency range of 3 kHz to 10
MHz (inclusive). Internal electric fields shall be determined as a vector average in a contiguous tissue volume of 2 × 2 × 2 mm. Internal electric fields induced by electric or magnetic fields including transient or very short-term peak fields shall be regarded as instantaneous values not to be time-averaged.
4. All other transmitters (effective radiated power (ERP) thresholds from 300 kHz through 3 THz in frequency):
(a) the RF source transmits at no more than the average power threshold result of the set of formulae based on the maximum permissible exposure (MPE) limits and
(b) the intended operation is normally separated at a distance from any part of the radiating structure of at least λ/2π, where λ is the free-space operating wavelength.

Every applicant for equipment authorization and every licensee prior to deployment or commencement of operations, seeking to be exempt, will use the
calculations in the rules to determine whether the device or transmitter falls under one of the four classes of exemptions.

Exemptions to RF Radiation Evaluations

All stations, regardless of power level (unless =<0dBm [1 mW]), must comply with the calculated or measured RF exposure limits.

Estimating Average Power

Stations [US based] are required to perform an evaluation of the strength of the RF fields around their stations. The FCC regulations on permissible RF exposure are not based on peak envelope power (PEP), but on average power over a 30 minute time period for uncontrolled environments or a 6 minute time period for controlled environments.

Operating Mode	Duty Factor	Note
Conversational CW	40%
AM (Carrier/modulated)	66% - 100%
Voice FM	100%
Conversational SSB	20%	1
Conversational SSB	40%	2
FSK or RTTY	100%
AFSK SSB	100%
Carrier	100%	3
FT4, FT8	50%	4

Note 1: Includes voice characteristics and syllabic duty factor. No speech processing.
Note 2: Includes voice characteristics and syllabic duty factor. Heavy speech processing employed.
Note 3: A full carrier is commonly used for tune-up purposes.
Note 4: Added to table.

To estimate your average power, first start with your Peak Envelope Power (PEP). Multiply that by the duty factor for the mode you are using, then by the maximum percentage of time you expect to operate within the averaging period.

For example, if you operate a 1500 watt PEP SSB phone station that is on for 10 minutes, off for 10 minutes and on for 10 minutes, you are operating with 200 watts average power (1500 watts PEP * 20% * 67% = 200 watts average power) over a 30 minute period.

If you operate a 1500 watt Morse Code (CW) station over the same time period, you have (1500 watts * 40% * 67% = 400 watts average power) over a 30 minute period.

In most cases for the 6 minute controlled environment exposure estimate, you should probably assume that it is possible to operate over the entire 6 minute period, so the 1500 watt PEP SSB phone station would be 300 watts average power for controlled-exposure calculations. An RTTY, digital station or FM repeater transmitter, could possibly be on for the full 30 minute time period, so the RTTY bulletin station or FM repeater would be 1500 watts average power. If it operated 10 minutes on, 10 minutes off and 10 minutes on, it would have 1000 watts average power over 30 minutes.
Hintlink - RF Exposure Calculator Help

What does this mean for amateur radio? A lot, because it's the first time that radio amateurs don't have special exceptions or exemptions in some way. They existed because of the almost infinite number of situations and supposed 'solutions' in most amateur configurations. The use of a truly online calculator (or one that says it's "online" but is downloaded and run locally in a spreadsheet or as a local executable) simply CANNOT in any way model anything but the simplest of situations. Parodoxically, it means nothing except for a "warm fuzzy feeling" that the FCC, Ofcom, etc. have done something to address an oddity in the use of parts of the radio spectrum. So, go through the motions to the best of your ability, stash away your results and get on with things. Just hope that they don't tighten things further in the forseeable future. Field modelling is sophisticated and expensive in time and money. It's sad that 5G is what triggered these changes because of exposure on 'social media' and bad press. Before this, few people thought of RF Exposure except for cell towers being placed at or near schools, which was mostly 'folly'.

FAQ
Q. Can I use this program on my web server?
A. Yes! RFSC is OpenSource under the GPU GPL licence and written in PHP/HTML.
However, credit to 'Paul Evans, VP9KF (G4BKI)' MUST be given.
Q. Can I use this program on my Windows/Mac/Linux machine?
A. Yes, it uses just about any browser on any machine. It's all done up at the server.
Q. Can I really use this program on my Windows/Mac/Linux machine?
A. You could run PHP on any of these platforms but you may have to be careful which version of PHP you use.
A smart individual could even build it as a WebApp to run within any Chromium-based browser (Chrome, Vivaldi, Edge, etc.)
Q. Are there other ways to do this?
A. Yes. There are some spreadsheets, executables, etc. However, these are pretty platform and software specific and more hassle.
Q. Are other sites running this?
A. Yes and no. A couple of sites are running it with modified front ends. It has not been used half as much as I would like, despite the OpenSource licence.
Q. Is there a forum to discuss this?
A. Yes, you can use the RF Exposure group at groups.io.

Fame and Fortune :-)
This calculator is used by radio amateurs ('hams') and professionals many hundreds of times per day.
It was featured on the ARRL RF Exposure web page for a number of years*, in RSGB's RadCom September 2015, p44/45, DX Zone Amateur Radio RF Safety Calculator page,
eHam.net, osha.gov, FCC, Pinterest and on many other web pages as a link.

*The ARRL, lately, have introduced their own copy of the calculator, online, converting PHP to JavaScript.

The author
Paul Evans, [BSc. (hons.) Physical Electronics, University of Warwick 1979] has been working around RF practically all of his life.
As Two Terminal ('diode') Device Manager at Plessey Microwave in the 1980s, wrote the 400+ page safety manual proposed for all of Plessey before it was bought in 1989.
This manual covered all aspects of safety in chemical handling, device processing (GaAs, InP and Si) and RF product testing as well as general site safety rules.
Paul has been a licensed radio amateur since 1972 (G4BKI) and also operates, since 1979, as VP9KF. He currently lives near Asheville, NC, USA.

References (some of these are 'circular' and quote a link back to here)
1) FCC RF-Exposure Regulations -- the Station Evaluation. ARRL web page, c1997. THIS WILL HAVE TO CHANGE sometime post 2021-05-03.
2. FCC OET Bulletin 65 Edition 97-01. THIS WILL HAVE TO CHANGE sometime post 2021-05-03.
3. FCC OET Bulletin 65 Edition 97-01B. THIS WILL HAVE TO CHANGE sometime post 2021-05-03.
4. RF Exposure ARRL web page