iPhones and RF energy? What to look for on spec?
February 22, 2022 6:14 AM Subscribe
I was holding an RF meter up to the oldest iPhone SE, and the new iPhone SE, and I noticed that even "at rest" they're emitting an order of magnitude higher RF energy (W/m^2), on average, than other iPhones (for which I measured with the same RF meter). More expensive iPhones seemed to roughly emit less RF energy at rest. I don't know much about electronics--does this have to do with a "radio" component? Is there a chart somewhere of differences between iPhone model "innards" that would likely correspond to these measurements?
I've tried googling things like
iphone rf components differences comparison se 11 12 13 pro chart
but I think I'm lacking the technical knowledge to get the thing I want.
I've tried googling things like
iphone rf components differences comparison se 11 12 13 pro chart
but I think I'm lacking the technical knowledge to get the thing I want.
The industry measurement you are looking for is SAR.
However, the time to have been worried about this is long in the past. The old analog (1G) phones put out FAR more RF energy (like ten TIMES) than modern digital (2G and up) phones. The amount of radiation emitted by each generation of phone is less and less, because firing that radio costs energy, and energy costs battery capacity, so manufacturers want to reduce it. You bought the phone to communicate, not to heat your head.
Further, RF energy is only harmful if it is ionizing, and at much much higher powers.
Lots more here:
https://www.google.com/search?q=cell+phone+radiation+measurement
(stick to the first three results; after that you start to get deeper into woowoo non-science garbage)
posted by intermod at 8:08 AM on February 22, 2022 [7 favorites]
However, the time to have been worried about this is long in the past. The old analog (1G) phones put out FAR more RF energy (like ten TIMES) than modern digital (2G and up) phones. The amount of radiation emitted by each generation of phone is less and less, because firing that radio costs energy, and energy costs battery capacity, so manufacturers want to reduce it. You bought the phone to communicate, not to heat your head.
Further, RF energy is only harmful if it is ionizing, and at much much higher powers.
Lots more here:
https://www.google.com/search?q=cell+phone+radiation+measurement
(stick to the first three results; after that you start to get deeper into woowoo non-science garbage)
posted by intermod at 8:08 AM on February 22, 2022 [7 favorites]
I don't know specifically what generations you're referring to, so this is a broad answer. This is also a bit of a hand-wavey answer given your description of knowledge of electronics.
To start of with, cell phone radiation is not a health concern. I state that definitively, as a professional in consumer electronics with a wireless communications background. That said, I suspect anything I say in this topic will not convince you of anything, so I will focus mainly on your observations of RF energy measurements.
New Apple iPhones support newer modulation schemes. These modulation schemes uniformly tend to have improved support for "beam forming" - using multiple transmitting antennas with slightly differing signals to create a "beam pattern" that puts more energy towards the receiving antenna and less energy in other directions. Beamforming allows the receiving antenna (cell phone) to receive more energy without the cell phone having to spend more energy on transmitting "louder". When a beamformed antenna is used, an RF meter will measure different readings depending on what side of the cell phone is measured. You may be getting falsely low measurements on one phone by measuring inside the beam path, but outside the beam path on another fun.
Phones also change their power level depending on the distance to the cell phone tower, and the amount of traffic that's present on the cell phone tower. If one phone connected to a cell phone tower across the street, and another phone connected to a cell phone tower several miles away, you could very well get a 10:1 difference in power measured. Don't assume cell phones always connect to the tower nearest to them - it could be the case that a nearby cell phone tower is overloaded, or may be prioritizing traffic from one cell provider over another. Further, as cell phone towers start to get overloaded, each cell phone connected to them will start to boost the power level to be "heard over the noise". I'm skipping a bunch of description of spread spectrum communication in CDMA phones here. You can roughly view cell phones as all being in a loud room talking at the same time. If you need to talk to someone across the room, the phone needs to be louder than everyone else in the room. This would also change the measured power from phone to phone.
Finally, I wouldn't actually trust any RF meter a consumer can buy for any reasonable amount of money (defined as less than $100K). To give an idea of the cost of doing accurate antenna measurements, to get better than 1 dB of accuracy generally requires the use of an anechoic chamber and precision measurement equipment that costs more than high end sports cars. If your measurement was in W/m^2 and the number went up by a factor of 10, that's 10 dB. I can believe inaccuracy on the order of 3-5 dB due to "multipath reflections" in your house (RF energy bouncing off surfaces in unexpected ways). In addition, you will measure any other cell phones in the house at the same time; it's distinctly possible your measurement is not isolated to the phone you think it is. There are many other potential error sources that make RF measurement very difficult to do repeatably or reliably.
posted by saeculorum at 9:19 AM on February 22, 2022 [16 favorites]
To start of with, cell phone radiation is not a health concern. I state that definitively, as a professional in consumer electronics with a wireless communications background. That said, I suspect anything I say in this topic will not convince you of anything, so I will focus mainly on your observations of RF energy measurements.
New Apple iPhones support newer modulation schemes. These modulation schemes uniformly tend to have improved support for "beam forming" - using multiple transmitting antennas with slightly differing signals to create a "beam pattern" that puts more energy towards the receiving antenna and less energy in other directions. Beamforming allows the receiving antenna (cell phone) to receive more energy without the cell phone having to spend more energy on transmitting "louder". When a beamformed antenna is used, an RF meter will measure different readings depending on what side of the cell phone is measured. You may be getting falsely low measurements on one phone by measuring inside the beam path, but outside the beam path on another fun.
Phones also change their power level depending on the distance to the cell phone tower, and the amount of traffic that's present on the cell phone tower. If one phone connected to a cell phone tower across the street, and another phone connected to a cell phone tower several miles away, you could very well get a 10:1 difference in power measured. Don't assume cell phones always connect to the tower nearest to them - it could be the case that a nearby cell phone tower is overloaded, or may be prioritizing traffic from one cell provider over another. Further, as cell phone towers start to get overloaded, each cell phone connected to them will start to boost the power level to be "heard over the noise". I'm skipping a bunch of description of spread spectrum communication in CDMA phones here. You can roughly view cell phones as all being in a loud room talking at the same time. If you need to talk to someone across the room, the phone needs to be louder than everyone else in the room. This would also change the measured power from phone to phone.
Finally, I wouldn't actually trust any RF meter a consumer can buy for any reasonable amount of money (defined as less than $100K). To give an idea of the cost of doing accurate antenna measurements, to get better than 1 dB of accuracy generally requires the use of an anechoic chamber and precision measurement equipment that costs more than high end sports cars. If your measurement was in W/m^2 and the number went up by a factor of 10, that's 10 dB. I can believe inaccuracy on the order of 3-5 dB due to "multipath reflections" in your house (RF energy bouncing off surfaces in unexpected ways). In addition, you will measure any other cell phones in the house at the same time; it's distinctly possible your measurement is not isolated to the phone you think it is. There are many other potential error sources that make RF measurement very difficult to do repeatably or reliably.
posted by saeculorum at 9:19 AM on February 22, 2022 [16 favorites]
Without knowing the exact readings, and what each phone is doing at the time it's extremely hard to answer your questions.
Typically, 3G cellphones transmit at about 1W or less (old-fashioned car phones can go up to 3W).
For 4G this can go down to 0.2W.
Wattage is even smaller for WiFi due to closer proximity (0.1W or smaller, as small as 0.015W / 15 mW).
As explained previously by others, device makers are squeezing EVERY LAST second of power, and they are not going to waste anything. Unless you live in a rural area with horrible bars your phone will never transmit at full power. They have every incentive to minimize power usage, and thus, transmission power.
Hope that answers your questions.
posted by kschang at 12:25 PM on February 22, 2022 [1 favorite]
Typically, 3G cellphones transmit at about 1W or less (old-fashioned car phones can go up to 3W).
For 4G this can go down to 0.2W.
Wattage is even smaller for WiFi due to closer proximity (0.1W or smaller, as small as 0.015W / 15 mW).
As explained previously by others, device makers are squeezing EVERY LAST second of power, and they are not going to waste anything. Unless you live in a rural area with horrible bars your phone will never transmit at full power. They have every incentive to minimize power usage, and thus, transmission power.
Hope that answers your questions.
posted by kschang at 12:25 PM on February 22, 2022 [1 favorite]
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Well - yes, definately - there are RF (radio frequency) chips for the LTE/cellular modem, WiFi and Bluetooth.
Depending on what is currently active (enabled in settings) and background/foreground apps running, those will be transmitting or not. More transmitting would mean higher EM/RF output.
Possibly - are the SE models smaller? Therefore their integrated antennas may be more concentrated in one area than a larger phone.
But as to why newer, none SE models would emit less RF? Possibly settings and apps.
posted by rozcakj at 7:14 AM on February 22, 2022