RF exposure

[AK9R]

Radiating element a few inches from your brain/eyes. Might be why there isn't a UHF or 7/800 version.

Let's talk about this.

The FCC issued new RF exposure rules in Report & Order 19-126 released May 3, 2021. The R&O went into effect May 3, 2023. The new rules generally apply to amateur radio.

Ed Hare W1RFI, retired from the ARRL Lab, wrote an article for QST explaining the rules, why they matter to amateur radio, and how to comply with the rules. Greg Lapin N9GL wrote a follow-up article for QST on the subject. The ARRL has an RF Exposure Calculator on their website, but you may be able to skip plugging all those numbers into the calculator as the W5YI Group and the ARRL have prepared some handy tables that will show you your ball park numbers depending on different conditions.

This YouTube video walks you through doing the calculations and shows how to use the tables.

Some example calculations for handheld radios transmitting while holding the antenna near your head:
Assuming transmitter output power of 5 watts, FM (duty cycle 100%), transmit 1 minute, receive 10 minutes, antenna gain 2.15 dBi, and a controlled environment
146 MHz -- minimum safe distance=0.5475 feet
446 MHz -- minimum safe distance=0.4491 feet
902 MHz -- minimum safe distance=0.3158 feet

Your microwave oven? Assuming transmitter output power of 1200 watts, FM (duty cycle 100%), transmit 5 minutes, receive 0 minutes, antenna gain 2.15 dBi, and a controlled environment. 2400 MHz -- minimum safe distance=10.3887 feet. That's why microwave emitters are interlocked with the door.

 

[prcguy]

A typical VHF rubber duckie antenna is well below 2.15dBi gain, so that would allow slightly higher power or a closer antenna. Some UHF handhelds have an antenna that is close to 2.15dBi gain but the typical power level is 4 watts. For 900MHz you rarely see a handheld radio over 3 watts.

 

[Lauri-CoyoteFrostbite]

.

That is really quite a Report and Order, and believe it or not, I actually read thru it in its entirety- enough however, that towards the end my eyes were starting to glaze over a tad (its a very quiet morning here that's actually snowing! ) .

My personal take away is that for radio amateurs there is nothing in this Order that changes anything....... this mostly codify's existing regulations and clears up certain numbers for some users.

But the causal reader can't fail to be impress'd by the extensive scope of licensed and unlicensed radio services in this country. Its easy to see why amateur radio is not a high regulatory priority with the FCC, and why, on the whole, they are pleased we are such a good self regulating service.... they have their hands full enuff.

----------------------

I have taken RF safety very seriously my whole professional career-- heck, for my whole life. It was once suggested by an ophthalmologist my mild cataracts were occupational from working around high powered microwave transmitters. That changed my work habits towards this stuff to even greater cautions.

And I do get questions all the time about RF exposures- one just the other day dealt with WiFi.

"Is the exposure to my router safe?"

I told her that, if she was like me right now she is being irradiated by a far nearer WiFi RF source than her router-- its coming from our laptop computers sitting on our laps.

---------------------------------------- I quickly had to calm her down !! **

Lauri


_______________________________________________________________

** hps.org



.

 

[MUTNAV]

Let's talk about this.

The FCC issued new RF exposure rules in Report & Order 19-126 released May 3, 2021. The R&O went into effect May 3, 2023. The new rules generally apply to amateur radio.

Ed Hare W1RFI, retired from the ARRL Lab, wrote an article for QST explaining the rules, why they matter to amateur radio, and how to comply with the rules. Greg Lapin N9GL wrote a follow-up article for QST on the subject. The ARRL has an RF Exposure Calculator on their website, but you may be able to skip plugging all those numbers into the calculator as the W5YI Group and the ARRL have prepared some handy tables that will show you your ball park numbers depending on different conditions.

This YouTube video walks you through doing the calculations and shows how to use the tables.

Some example calculations for handheld radios transmitting while holding the antenna near your head:
Assuming transmitter output power of 5 watts, FM (duty cycle 100%), transmit 1 minute, receive 10 minutes, antenna gain 2.15 dBi, and a controlled environment
146 MHz -- minimum safe distance=0.5475 feet
446 MHz -- minimum safe distance=0.4491 feet
902 MHz -- minimum safe distance=0.3158 feet

Your microwave oven? Assuming transmitter output power of 1200 watts, FM (duty cycle 100%), transmit 5 minutes, receive 0 minutes, antenna gain 2.15 dBi, and a controlled environment. 2400 MHz -- minimum safe distance=10.3887 feet. That's why microwave emitters are interlocked with the door.

Yup.... minor correction / possible point of discussion.. I'm not positive, but I think microwave ovens use magnatrons, which are traditionally pulsed.

Thanks
Joel

 

[MUTNAV]

.

That is really quite a Report and Order, and believe it or not, I actually read thru it in its entirety- enough however, that towards the end my eyes were starting to glaze over a tad (its a very quiet morning here that's actually snowing! ) .

My personal take away is that for radio amateurs there is nothing in this Order that changes anything....... this mostly codify's existing regulations and clears up certain numbers for some users.

But the causal reader can't fail to be impress'd by the extensive scope of licensed and unlicensed radio services in this country. Its easy to see why amateur radio is not a high regulatory priority with the FCC, and why, on the whole, they are pleased we are such a good self regulating service.... they have their hands full enuff.

----------------------

I have taken RF safety very seriously my whole professional career-- heck, for my whole life. It was once suggested by an ophthalmologist my mild cataracts were occupational from working around high powered microwave transmitters. That changed my work habits towards this stuff to even greater cautions.

And I do get questions all the time about RF exposures- one just the other day dealt with WiFi.

"Is the exposure to my router safe?"

I told her that, if she was like me right now she is being irradiated by a far nearer WiFi RF source than her router-- its coming from our laptop computers sitting on our laps.

---------------------------------------- I quickly had to calm her down !! **

Lauri


_______________________________________________________________

** hps.org



.

Although I always wonder about the non-thermal effects of non-ionizing radiation. I remember reading something about the movement of calcium ions in unusual ways when exposed to low RF levels.

But considering how your friend reacted, and how people react to terrible things like how granite countertops can be slightly radioactive, it's probably best not to bring the subject up.

Thanks
Joel

 

[prcguy]

Yup.... minor correction / possible point of discussion.. I'm not positive, but I think microwave ovens use magnatrons, which are traditionally pulsed.

Thanks
Joel

Microwave oven magnetrons run CW. I had one that was torn apart to experiment with extracting gold from ore. It didn’t work very well and vaporized most of the gold, no easy way to vary the power to creep up to the melting point.

 

[Lauri-CoyoteFrostbite]

Yes Joel, a microwave oven is quite a powerful radio transmitter-- good thing its radiation is confined.

I was am advisor to a high school science club and we --- pausing a moment to consider if I should admit this (but the statues should have run by now ) --------- We took the magnetron and its associated electronics out of an oven, attached it to a horn antenna, setting it up as a 'demo unit.'

The bloody thing would light fluorescent bulbs across a class room.

What other things we did with it will remain my secret, though I am sure school science class's would never sanction this today.

.

 

[MUTNAV]

Microwave oven magnetrons run CW. I had one that was torn apart to experiment with extracting gold from ore. It didn’t work very well and vaporized most of the gold, no easy way to vary the power to creep up to the melting point.

Yup... your right, I actually had to look it up to verify, I'm used to ones used in radars, ( which use pulses most of the time anyway ).

I really like the external magnet ones (very powerful magnets that would destroy magnetic resistance watches)

Thanks
Joel

 

[MUTNAV]

Yes Joel, a microwave oven is quite a powerful radio transmitter-- good thing its radiation is confined.

I was am advisor to a high school science club and we --- pausing a moment to consider if I should admit this (but the statues should have run by now ) --------- We took the magnetron and its associated electronics out of an oven, attached it to a horn antenna, setting it up as a 'demo unit.'

The bloody thing would light fluorescent bulbs across a class room.

What other things we did with it will remain my secret, though I am sure school science class's would never sanction this today.

.

But.... That's how we learn....

I was thinking along the lines of pulsed RF effecting the bodies systems at levels that aren't a thermal heating concern.

(no, not mind control, but possible other effects)


I don't know if you've seen this, but.... but it's a humorous mocking of over-reactions.

Thanks
Joel

 

[prcguy]

Yup... your right, I actually had to look it up to verify, I'm used to ones used in radars, ( which use pulses most of the time anyway ).

I really like the external magnet ones (very powerful magnets that would destroy magnetic resistance watches)

Thanks
Joel

I’ve worked on a few marine radars but mostly pulsed, swept frequency ones used for radar cross section measurements. Those were synthesized sources externally pulsed with pin switches then run to solid state or TWT amplifiers. The power was never very high on those due to the very sensitive receivers used and I’ve stood in the measurement area at full power much of my radar carrier. I was even the human radar cross section model for General Motors with the early adoption of 76GHz for vehicle avoidance radar.

 

[hp8920]

Actually, you’re both right with the microwave. The magnetron is CW. However, the HVDC filter caps in residential microwave oven power supplies can’t hold up the load, so they’re effectively pulsed at 120 Hz. Industrial and some commercial microwave ovens are true CW.

Also a 1 kW microwave oven has an effective heating output of 500 W and a RF output only a little higher. That’s the disclaimer about IEC rating. It has to do with rating based on the input DC power of magentrons, which back in the day, were about 50% efficient.

 

[Lauri-CoyoteFrostbite]

Some of my work projects took me out to Kwajalein Atoll in the Marshall Islands--- the Army base best known (then) for the "Star Wars" tests.

Its a beautiful island with an the lagoon right out of Paradise-- with idyllic white sandy swimming beaches and crystal blue waters. Its magical.
But the whole island- the whole atoll-- is one big microwave oven--- however some places were more oven than others.

I and a friend decide to try one of the more isolated swimming beaches on the far west side of the island-- We had hardly spread our towels on the sand when an MP truck drives up and two guys in uniforms jump'd out.

"What do you two women think your doing !?" they yelled at us
"Didn't you see the signs !!?

"(Duh) No?"

"Well they are right over there" pointing back to the paved road.
-------------------We had come from along the beach.

"You two are right in the (beam) path of (Brand X) !!" **

"Oh, guess we better leave, huh ?
_______________________________________________________

Ok, so we move way down the island, checked for signs --- no signs, -everything looked good.

We had hardly gotten into the water when the same truck pulled up again

"What the hell do you two think your doing now ??!!

"What is it now ?! I shouted back
"What (F'ing) beam path are we in Now ??!

"You two are swimming in the area where garbage is dumped....didn't anyone tell you about the sharks in here??"

________________________________________________________

There's the Yuk-We club on the base with this great bar. No beam paths, no sharks--- We decided swimming was over for the day-



** A Ziga-watt phased array radar

 

[Lauri-CoyoteFrostbite]

• My work projects took me out to Kwajalein Atoll in the Marshall Islands--- the Army base best know (then) for the "Star Wars" tests.
  
  Its a beautiful island with an the lagoon right out of Paradise-- with idyllic white sand swimming beaches and crystal blue waters. Their is magical.
  
  The whole island- the atoll-- is one big microwave oven--- but some places were move oven than others.
  
  I and a friend decide on one of the more isolated swimming beaches on the far west side of the island-- we had hardly spred our towels on the sand when this truck drives up and two guys jump'd out.
  
  "What do you think your doing !?" they yelled at us
  "Didn't you see the signs !!?
  
  "(Duh) No?"
  
  "Well they are right over there" pointing to the paved road. We had come from along the beach.
  
  "You two are right in the (beam) path of (Brand X) !!"
  
  "Oh, guess we better leave, huh ?
  _______________________________________________________--
  
  Ok, so we move way down the island, checked for signs --- no signs, everything looked good.
  
  W

 

[MUTNAV]

I’ve worked on a few marine radars but mostly pulsed, swept frequency ones used for radar cross section measurements. Those were synthesized sources externally pulsed with pin switches then run to solid state or TWT amplifiers. The power was never very high on those due to the very sensitive receivers used and I’ve stood in the measurement area at full power much of my radar carrier. I was even the human radar cross section model for General Motors with the early adoption of 76GHz for vehicle avoidance radar.

I was weather maintenance for a short time, in school for the old FPS-77 Radar (sheet metal dish), which had tons of power from an external magnet magnatron.

It's also where I learned that electrons from an electron gun in the CRT can actually chip the front glass of the CRT.

Thanks
Joel

 

[eorange]

When I key up my HT while in front of my LED monitor...the display significantly increases in brightness. Still haven't figured that one out yet.

 

[iMONITOR]

I wonder how these are for encouraging hair growth?

HYS 25 Watt UHF HT

 

[ab3a]

Although I always wonder about the non-thermal effects of non-ionizing radiation. I remember reading something about the movement of calcium ions in unusual ways when exposed to low RF levels.

But considering how your friend reacted, and how people react to terrible things like how granite countertops can be slightly radioactive, it's probably best not to bring the subject up.

Thanks
Joel

People have been wondering about "non-thermal" effects for a long time. The fact is that none of the science on non-thermal effects has ever been repeated. There isn't even a good physical theory as to how these effects are supposed to work. People who understand electronics and antenna engineering as well as medical research protocols are extremely scarce. Frankly, lots of research ends up with problems in either one place or another. This is why so few of them have results that have been confirmed in other experiments.

That said, Thermal effects are fairly well understood. It is also possible that pulse averaging may not be entirely accurate. Some materials may be thermal insulators that high energy pulses may shine through. The heat would accumulate because it doesn't dissipate fast enough. This would be an unusual situation in human tissue, but it's not impossible.

So the standards have fudge factors of 10 built in to them. I know this because I corresponded with a professor who was on the IEEE standards committee back in the early 1990s. He didn't think much of the notion of that fudge factor. More to the point: The exposure standard used to be 10 mW/cm^2 across the board. Then they arrived at the wavelength based standard --for "reasons." There was probably a lot of posturing and what-about-isms that often plague standards committees. Anyhow, that's where the standards we have today come from.

To summarize: Non-thermal effects of RF have not been demonstrated in a repeatable experiment. And believe me, many researchers have looked hard. Part of the problem is the use of the term "Radiation" with RF. It scares people in to thinking that if they were exposed, that their kids will turn out funny. Yet they don't hesitate to jam a cell phone right next to their heads with its half dozen radios radiating at one time or another. If RF was truly a hazard, people should have been dying all over the place when cell phones became popular.

So yes, I do my duty as ham. But I also know that these standards are based on lots of confabulation and bluster. If you're determined to find something to worry about, this should be pretty far down on your list of threats to your wellbeing.

 

[prcguy]

People have been wondering about "non-thermal" effects for a long time. The fact is that none of the science on non-thermal effects has ever been repeated. There isn't even a good physical theory as to how these effects are supposed to work. People who understand electronics and antenna engineering as well as medical research protocols are extremely scarce. Frankly, lots of research ends up with problems in either one place or another. This is why so few of them have results that have been confirmed in other experiments.

That said, Thermal effects are fairly well understood. It is also possible that pulse averaging may not be entirely accurate. Some materials may be thermal insulators that high energy pulses may shine through. The heat would accumulate because it doesn't dissipate fast enough. This would be an unusual situation in human tissue, but it's not impossible.

So the standards have fudge factors of 10 built in to them. I know this because I corresponded with a professor who was on the IEEE standards committee back in the early 1990s. He didn't think much of the notion of that fudge factor. More to the point: The exposure standard used to be 10 mW/cm^2 across the board. Then they arrived at the wavelength based standard --for "reasons." There was probably a lot of posturing and what-about-isms that often plague standards committees. Anyhow, that's where the standards we have today come from.

To summarize: Non-thermal effects of RF have not been demonstrated in a repeatable experiment. And believe me, many researchers have looked hard. Part of the problem is the use of the term "Radiation" with RF. It scares people in to thinking that if they were exposed, that their kids will turn out funny. Yet they don't hesitate to jam a cell phone right next to their heads with its half dozen radios radiating at one time or another. If RF was truly a hazard, people should have been dying all over the place when cell phones became popular.

So yes, I do my duty as ham. But I also know that these standards are based on lots of confabulation and bluster. If you're determined to find something to worry about, this should be pretty far down on your list of threats to your wellbeing.

I know some people who claim to be sensitive to RF where they will go into a room with a Wi-Fi access point, see the access point then hold their head and scream in pain claiming the RF is killing them. Not sure how that would go if the room had the same access point and it was hidden. Anyway, maybe we should employ these people as “canaries in a cage” and use them like minors did to test for bad air.

 

[mmckenna]

I've run into too many whackos as well as too many guys that spent a lot of their lives up on towers, yet magically have a lot of kids. Unfortunately there is a lot of bad science, a lot of people who don't understand the first thing about RF, understand the difference between ionizing and non-ionizing radiation, and a lot of people that live in fear of what they do not understand. Thanks to the wonders of the internet, there's plenty of support for the RF whackos that will happily feed their fears.

I don't let any of it scare me. I also don't take stupid risks.

Occupational use of a hand held radio (which is what we were originally talking about in the thread AK9R was referring to) doesn't worry me that much. Having a radiating antenna a few inches from my skull isn't high on my list of things I'd do long term.

We went through all this locally when smart meters were deployed by the local utility. The number of people that had no clue what they were talking about was impressive. It was a little bit of fun to mess with them.

 

[Lauri-CoyoteFrostbite]

I have never been anything but cautious around RF. When I was told my cataracts might have come from my microwave exposure. I did start being more careful-- but 'cel fones, hand held radios and proximity to radiating low-to-high frequency antennas and equipment never has been an issue.
I was impressed, though, when I once visited the million watt VLF Naval radio station NSS, and was startled by the signs that said-

---Danger----
Radiation Hazard
Keep Moving !

Keep Moving ..... Holy Cow !....
I couldn't get the image I was on that rotating plate inside a microwave oven--cooked evenly; no hot spots.
_____________________________________________________________________

I will admit that as a grad student I and a fellow TA did some things that were not too kosher-
Like playing "Trolling for Tail Lights" on a busy California freeway with a portable X-Band transmitter.
(It was quite a sport until we trolled a High Patrol car.............. )

But in the spirit of science, but more along the lines of sticking beans up our noses to see what would happen, we both once put our hands into the beam of a C-band horn.

Yes! indeed they got warm !

What was a remarkable lesson here, however, was with only a few seconds exposure our nail polish had been cleanly stripped from our fingers.
No one has ever offered a explanation.

.