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RF Safety Calculator (Power density) help page (2020-04-01) Changes. WIP. Visit back for latest updates.

New FCC proposals were published on 2020-04-01
New FCC rules have been published.
They come into effect on June 1, 2020. Delayed indefinitely while OMB reviews and Federal Register publishes new date [this change was made on June 2, 2020!!].

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

The Routine RF Radiation Evaluation discussed here is only mandated by the FCC for USA-based radio amateurs.
It may be used by you personally to gain an overview of your exposure in another country.
Other countries may adopt the FCC guidance, in which case it may apply to you, albeit with modified levels (check!)
**If you have a US licence, yet live abroad and use another callsign, you may be affected for ALL your transmissions.**

Hintlink - RF Safety Calculator Help
History Current Software Release: v1.3  ( Friday, 06-Dec-2019 11:06:47 PST ). Current Help Release: v1.0  ( Wednesday, 27-May-2020 07:33:25 PDT )
1985-10-08 FCC OET Bulletin 65
1997-08-10 FCC OET Bulletin 65 Edition 97-01
FCC OET Bulletin 65B Edition 97-01
2007-10-21 v0.1 beta release.
2012-02-04 v1.0 release. First user proven release.
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 progresses.
. FCC 19-126A1 published.
2020-04-01. FCC publishes partial new FINAL rules in Federal Register (FR). No comment period was used but was proposed in FCC 19-126A1.
2020-04-06. FCC publishes remainder with "Comments are due on or before May 6, 2020 and reply comments are due on or before May 21, 2020."
Remainder means: >6 GHz, averaging (time & area), WPT (wireless power transfer; local control and remote controlled)
2010-04-15. FR corrects previous to "Comments are due on or before May 15, 2020 and reply comments are due on or before June 15, 2020."
2020-05-02. FR corrects previous to "Comments are due on or before June 3, 2020 and reply comments are due on or before July 6, 2020."

ARRL states "[FCC calculator] would be preferable to unofficial third-party calculators, the results from which might not be accorded the same degree of deference in local disputes. Several software programs were suggested as models." If this occurs, this page, over time, may be removed.

Other factors

Exemptions to Routine RF Radiation Evaluations

On 1997-08-27, in the  Second Memorandum and Order, the FCC adopted a sliding scale for categorical exemption to routine RF radiation compliance testing, based on peak envelope power (PEP) at various Amateur Radio operating frequencies. While the RF radiation exposure compliance levels are based on average power, the categorical exemptions from the requirement for periodic station compliance testing are based upon peak envelope power (PEP). Stations operating at or below these respective PEP levels are categorically excluded from having to perform a routine RF radiation evaluation. However, all stations, regardless of power level, still must comply with the RF exposure limits.

Frequency (MHz) Band (m)
Peak Envelope Power (W)*
1.800 - 2.000 160
3.500 - 4.000 80
5.351.5  - 5.366.5
500 [band added since publication(s)]
7.000 - 7.300 40
10.100 - 10.150 30
14.000 - 14.350 20
18.068 - 18.168 17
21.000 - 21.450 15
24.890 - 24.990 12
28.000 - 29.700 10
50.000 - 54.000 6
144.000 - 148.000 2
222.000 - 225.000 -
420.000 - 450.000 70 cm
902.000 - 928.000 -
1240.000 - 1300.000 -
2300.000 and higher -
* Subject to power limit by band/licence

New - 2019-12-05.... FCC proposals
Internal electric field (Ei) limits to be set between 3 kHz and 10 MHz.
Specific absorption rate (SAR) to be used between 100 kHz and 6 GHz.
Power density (PD) to be used above 6 GHz.
[creates a 'break point' at 10MHz in the amateur bands]
Change to regime of:
Exemption - Evaluation - Mitigation
[ general population / uncontrolled ] vs [ occupational / controlled ]
For amateur radio this means: Neighbours and public vs Members of household
1 mW exemption 'no matter what'

Very odd change above 6GHz; minimum changed from 5 cm to zero (distance from skin)

Average Power Estimate

[US based] Amateurs are required to perform a routine evaluation of the strength of the RF fields around their stations, subject to certain exemptions based on peak envelope power (PEP) levels at [on] the various amateur bands. However, 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. The part of the regulations that determine whether a station operator must perform a periodic evaluation, however, is based on PEP.

Operating Mode Duty Factor
Morse code (CW) 40%
SSB phone 20%
FM 100%
RTTY/Digital 100%
FT4, FT8*
AM 100%
* Added to table

Newer table - 1997-10-18
Operating Mode Duty Factor Note
Conversational SSB 20% 1
Conversational SSB 40% 2
Voice FM 100%
FSK or RTTY 100%
Conversational CW

FT4, FT8
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 PEP * 40% * 67%, or 400 watts average power.

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 or digital bulletin station, or FM repeater transmitter, would probably 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.

New - 2019-12-05.... FCC proposals
Averaging is again under review and considerable change may result. WIP

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.
Can I really use this program on my Windows/Mac/Linux machine?
A. You could run PHP on any of these platforms.
A smart individual could even build it as a WebApp to run within any Chromium-based browser (Chrome, Vivaldi, Opera, 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.

Fame and Fortune :-)
This calculator is used by radio amateurs ('hams') and professionals many hundreds of times per day.
It is featured on the current ARRL RF Exposure web page, 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.

ARRL RSGB DXZone eHamnet OSHA FCC Pinterest

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.
FCC OET Bulletin 65 Edition 97-01
3. RF Exposure ARRL web page

Further footnotes
Lennart Hardell and Michael Carlberg, Int J Oncol, NIH
Mehdizadeh A R. and Mortazavi S. M. J. J Biomed Phys Eng, NIH
The Challenges of J-shaped Dose Response Models for Ionizing and Non-ionizing Radiations, SMJ Mortazavi

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