Hintlink - RF Safety Calculator Help

RF Safety Calculator (Power density) help page

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.

Scope
The Routine RF Radiation Evaluation discussed here is only mandated by the FCC for US-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!)

History Current Software Release: v1.3 ( 2019-12-06 ). Current Help Release: v0.3b ( 2019-12-07 )
1985-10-08 FCC OET Bulletin 65
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.
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.

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	500
3.500 - 4.000	80	500
5.351.5 - 5.366.5	60	500 [band added since publication(s)]
7.000 - 7.300	40	500
10.100 - 10.150	30	425
14.000 - 14.350	20	225
18.068 - 18.168	17	125
21.000 - 21.450	15	100
24.890 - 24.990	12	75
28.000 - 29.700	10	50
50.000 - 54.000	6	50
144.000 - 148.000	2	50
222.000 - 225.000	-	50
420.000 - 450.000	70 cm	70
902.000 - 928.000	-	150
1240.000 - 1300.000	-	200
2300.000 and higher	-	250

* Subject to power limit by band/licence

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*	50%
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%
AFSK SSB	100%
Conversational CW	40%
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 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.

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.
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.

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