Are Helium Hotspots dangerous to be around? How much RF energy do they emit? Should you or your hosts be worried about the exposure levels? Let’s run through the facts, then you can make your own decision.
We’ll start with this: In general, Helium Hotspots rarely emit any RF. They’re built to receive signals far better than transmit them. That’s because the whole point of the network is to “listen” for really faint signals from sensors at long range.
Still, Helium Hotspots DO occasionally transmit out power in the form of a “beacon”. Beaconing usually happens less than 3 times per day. Sometimes you’ll have a banner day and it’ll beacon 5 times. That’s unusual, so I’ll use 3 or less when making the calculations below. Just to be clear:
A beacon is a single transmission witnessed by any Hotspot.
https://docs.helium.com/blockchain/proof-of-coverage/
In this case you can ignore the “witnessed by a hotspot” aspect. For now we’re focusing solely on the power in a beacon, not whether or not it was received.
You can see how often your hotspot beacons just by checking on Helium Explorer. Here’s an example from one of mine on an unusually active day:
Yep, 2 beacons inside of 5 hours. We are bangin’! By the way, for those of you concerned with earning HNT, your “slice of the pie” for beaconing is relatively low, so don’t worry about “not beaconing enough”. Once a day is fine.
Back to RF exposure and power! Helium uses LoRa as a radio protocol, and what we call a “beacon” is technically a “chirp”. Let’s dig a little deeper on that. From Helium’s blog:
LoRa uses what is known as a “chirp” protocol and spreading factors (SF) are the duration of the “chirp”. Typically you’re looking at a range of SF7 to SF12 where the 7 is the shortest time on air. Each step up doubles the time on air to transmit the same amount of data and increases the range. Due to local restrictions, we are limited by max payload sizes to certain spreading factors, usually SF8 and SF9 for most packets.
https://engineering.helium.com/2020/10/02/spreading-factor-changes-poc.html
How long does an SF8 or SF9 (or even an SF 12) chirp last? Let’s take a look at this table from Semtech (the owner of LoRa technology). Here’s a screenshot:
There are 1,000 milliseconds (ms) in a second, so for all chirps, we’re looking at under a second of time that RF is being emitted.
Cool, so now we have a time established: Less than one second per beacon.
The next (obvious) question is: How strong are these beacons?
For those of you who’ve read the Cable Loss & EIRP post, you’ll remember that the most powerful hotspots (American hotspots) blast out a massive 27 dBm. I’m joking about the massive part. dBm stands for Decibel MilliWatts, and 27 is about half a watt. You can do this calculation yourself over at DigiKey’s website. I’ll make it easy and just paste it in here:
I can hear you say it: “Ok Nik, but what about when someone uses a MAXIMUM GAIN! (said in my best monster truck voice) antenna? In the US, the legal max antenna gain we can use is 9 dBi.
27 dBm + 9 dBi = 36 dBm. So, how many watts is that? Let’s cruise back to DigiKey’s calculator and see.
Holy smokes, almost 4 watts! That’s enough to fry a… Wait a second. How much power is 4 watts? Is there anything else we might possibly use for comparison?
Yep, you guessed it. Cell phones. Cell phones in general have 2 “levels” of power they emit: .6 watts, and 3 watts. Typically, most people use their cell phones while holding them within 2 feet of their face. If you have long-ass gibbon arms, maybe you can get it 3 feet away from your face. You can reduce your exposure by growing your arms or just following common sense guidelines.
When you are talking on a phone is when it emits the most power; it has to transmit your voice. At that point, you are holding a device to your head for more than a second (if watching people in public is any indication, it’s more like non-stop) that is emitting up to 3 watts.
Let’s go back to the Helium Hotspot one last time and just think about where it’s placed. While I recommend always placing it outside (NOT for RF exposure reasons, but to provide the best coverage), some people can’ t do that due to HOA or other building restrictions. So let’s assume worst case: In your house.
If it’s in your house, it’s unlikely that you hold your Helium Hotspot to your head. It’s probably on a table or by a window. Let’s say it’s reasonable to be at least 3 feet away from the antenna at all times. We’ll do a quick calculation check on that distance with the MAXIMUM POWER antenna to see what you’re being exposed to, using HintLink’s RF Exposure Calculator. By the way, a 9 dBi omni antenna (the maximum gain you can legally use) is about 4 feet long. Most people don’t like the way a 4′ long fiberglass pole looks inside the house.
Since I’ll assume that you’re not working in a Controlled Environment (think RF labs, or near super high RF emitters like a cell tower site), we’ll calculate the exposure based on the max limits you’d encounter in your ordinary life. In that case, (ah, fuck it, I’ll make this huge because this is my final answer.)
A Helium Hotspot emits .07% of the Maximum Permissible Exposure to RF devices. It does that for less than a second, less than 4 times per day.
I do know that some people are super sensitive to RF. If that’s you, it may not be the best idea to participate in the building the world’s largest wireless network. For the rest of ya, go deeper if you want, but after looking into it, this seems like enough for me to say that the RF being emitted from a Helium Hotspot is not something I’m going to worry about.
If you need more help with understanding Helium, whether you have antenna questions, want help with optimization, or just want to talk through the Helium ecosystem and how you can fit in, take a look at joining the Gristle Crüe.
Rock on!
Hi Nik,
This confirms my speculation on this matter, especially as regards beaconing, power and listening time. I do wonder about p2p and OTA comms, though, mostly as related to all these updates that come from Helium and the vendors. It sounds like gobs of data going over air rather than the internet. A comment on that and maybe a link would be appreciated. Thank You!
John
Thanks Gristle, you have been granted PhD level cert in Quantum Splaining.
Toxic RF effects from HS is FUD fodder and seemingly not a rational consideration.
Sooooooo many other things to worry about. Death by land shark or Discord overdose lead the list, well behind lethal antenna installation mishaps.
Nik,
Thank you for sharing your knowledge of Helium. I have found your explanations very helpful. However, I don’t find the statement that miners only transmit when they are sending a beacon to be true. Personally, I think the RF exposure is insignificant, but I just want to set the record straight.
Remember, that the point of Helium is to create a world wide LoraWAN network so that sensors and “things” can connect wirelessly to the internet from anywhere. You are correct in stating that miners are optimized for listening to sensors, however they can still transmit to devices. (I am not the most up to date on Helium hardware, but I think each miner can listen to eight sensors at a time, but can only talk ot transmit to one sensor at a time)
I will provide an example: There is a GPS vehicle tracker available that can also immobilize the car if it is stolen. It uses the Helium network to communicate, as it is significantly cheaper than paying for a cellphone plan for the device. Normally the tracker is sending GPS location data to a miner, and the miner relays that data to the internet, so the owner can look at it on a website or app. This represents a listen or receive case. However, if the car is stolen, the owner can immobilize the using the internet. The miner then talks or transmits RF to the vehichle tracker signaling it to stop the car.
In conclusion, miners do emit RF energy. How often, depends on what people are willing to pay for.
Jacob, totally makes sense, thanks for clarifying. Do you have any info regarding duration/power and if that will differ from a beacon?
Thank you very much! Very informative.
So is the max 9dbi because above it is harmful? For example a 15 dbi antenna and the hotspot will produce 15 W. It still doesn’t look like dangerous if comes only 5 times a day and each time less than a second. Right?
Very insightful. Can you address “Jacob Ertel” comment above?
9 dBi is the max in the US due to FCC regs. Due to the way LoRa propagates, there’s no real sense in using a 15 dBi antenna for Helium Hotspots
Hi BB, what part did you want addressed?
Hi, I was wondering if it would be safe to have a miner in the same room as you all day? 2.3 DBI
Probably safer than the other EMF in that room if you’ve got a computer, phone, etc. 🙂
Hola Nick.
Tengo la duda sobre si el hotspot hará interferencias en un audífono y en un implante coclear
I wouldn’t think so, I’d think they’re using/picking up very different frequencies. Ya can’t hear 915 with the human ear, as far as I know.
Correct cochlea implant speech processors only sample the audible spectrum. 2k-22kHz
The human ear is 2k to 22kHz. The quarter wavelength cut off for 915MHz is 228MHz.
Love the depth of knowledge you have, thanks for contributing! ~Nik
I notice there’s always a lot of confusion between RF (radio waves) and sound. Allow me to explain:
Frequency is simply a unit of measurement based on timescale. Specifically, the unit hertz is the amount of times a wavelength repeats within the timespan of a second. For example, 120V 60 Hz AC power (the US power standard) reverses polarity 120 times a second, because you have to go from positive, to negative, then back to positive to complete a 360 degree cycle, thus what makes the current “alternating”. This makes it complete 60 full cycles a second. 60 Hz.
The distinction between sound waves and radio waves is the medium of transport.
Sound is a pressure wave caused by physically moving molecules, be them water, air, or anything else that can vibrate when struck. Pressure changes form the polarities of our “waves” with changes to positive or negative pressure compared to static. If these pressure waves reach our ears at anywhere from 20 Hz to 20 kHz, our eardrums will conduct these pressure changes and perceive them as sound. In space, which is an empty vacuum, there is no matter to conduct your pressure waves, and thus sound cannot travel.
Radio, visible light, radar, microwave, 5G, are different frequencies of the same spectrum of non-ionising radiation (not to be confused with nuclear radiation). We can see the sun and other objects of space because these “waves” are in the form of photon particles radiating from a source. Photons, without going to deep into the physics of it, change polarity at a frequency as they travel through time, thus inhabiting some part of the spectrum of RF (radio frequency). Light is just the spectrum of RF that we can perceive.
The most important frequency range for human speech is 1000-4000 Hz. Even if we somehow had RF at 2000 Hz, you would not be able to hear it, because humans cannot hear light.
Thanks Aean, excellent points and much appreciated that you took the time to go through all that. Rock on!
Still unconvinced of the safety. In the documentation for multiple different Helium miner devices I found online, it states “This equipment should be installed and operated with minimum distance 20cm between the radiator and your body.” 20cm = 7 inches. If it’s far less radiation than a cell phone why does it come with this kind of warning??