Does A Helium Hotspot Actually Expose You To Powerful Radiation?



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.

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.

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!


18 responses to “Does A Helium Hotspot Actually Expose You To Powerful Radiation?”

  1. John Hickmott Avatar
    John Hickmott

    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!


  2. 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.

  3. 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.

  4. Jacob, total­ly makes sense, thanks for clar­i­fy­ing. Do you have any info regard­ing duration/power and if that will dif­fer from a beacon?

  5. Mohammad Avatar

    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?

  6. Very insight­ful. Can you address “Jacob Ertel” com­ment above?

  7. 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

  8. Hi BB, what part did you want addressed?

  9. Hi, I was won­der­ing if it would be safe to have a min­er in the same room as you all day? 2.3 DBI

  10. Prob­a­bly safer than the oth­er EMF in that room if you’ve got a com­put­er, phone, etc. 🙂

  11. Mikel Izpura Pinillos Avatar
    Mikel Izpura Pinillos

    Hola Nick.
    Ten­go la duda sobre si el hotspot hará inter­fer­en­cias en un audí­fono y en un implante coclear

  12. 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.

  13. Cor­rect cochlea implant speech proces­sors only sam­ple the audi­ble spec­trum. 2k-22kHz

  14. The human ear is 2k to 22kHz. The quar­ter wave­length cut off for 915MHz is 228MHz.

  15. Love the depth of knowl­edge you have, thanks for con­tribut­ing! ~Nik

  16. 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.

  17. Thanks Aean, excel­lent points and much appre­ci­at­ed that you took the time to go through all that. Rock on!

  18. 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??

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