Helium 101: Cable Loss and EIRP.



Got ques­tions about what kind of cable you should use to con­nect your Heli­um hotspot to your anten­na? Want a Heli­um-spe­cif­ic cable loss table?

You’re not alone! Lots of folks want to know if they should use LMR 240 or 400 or 900, or how long it can be, or if they should use the cable that came with their cheap‑o eBay antenna. 

In order to answer that, I’m going to walk you through how the whole thing works. That way, instead of ask­ing me if your XX anten­na with YY feet of ZZ cable will work, you’ll know how to cal­cu­late the answer. 

First, let’s talk about the pre­cise but con­fus­ing ter­mi­nol­o­gy in the land of RF (Radio Fre­quen­cy). Well, if you want to just skip to the cable loss tables, go here.

You’ll com­mon­ly see dB (deci­bel), dBm (deci­bel mil­li­Watt), and dBi (deci­bel isotrop­ic) thrown around, as well as dBm, EIRP, ERP, FSL, and oth­ers. Sheesh, that’s a lot!

We’ll start with dB, which stands for “Deci­bel”. A deci­bel is the dif­fer­ence between two sig­nal lev­els. RF engi­neers (and the rest of us) use it to add or sub­tract the effect of cables (or oth­er “sys­tem devices”) on sig­nal strength. 

dB are log­a­rith­mic: Every time you add 3 dB of gain, you dou­ble to the sig­nal lev­el. Every time you halve pow­er, you sub­tract 3 dB. That means a 3 dBi anten­na is dou­bling your emit­ted pow­er over a zero gain anten­na! But wait…that can’t be right, can it? Anten­nas don’t “add” energy.

As I’ve cov­ered in oth­er blog posts, anten­nas focus and shape ener­gy. They don’t add ener­gy. It’s kind of like a gar­den hose sprayer with mul­ti­ple spray pat­terns. The water pres­sure going into the noz­zle does­n’t change, but as you switch from “mist” to “show­er” to “stream”, your emit­ted pat­tern changes.

That pat­tern change, and the result­ing focus and range, is mea­sured in dBi (deci­bel isotropic). 

Ok, it’s about to get a lit­tle more con­fus­ing, but I promise you can under­stand this. 

Isotrop­ic” refers to hav­ing the same ener­gy val­ue in all direc­tions. It’s the idea that an anten­na could emit a per­fect­ly shaped “globe” of ener­gy. For var­i­ous rea­sons, it’s impos­si­ble to build an isotrop­ic anten­na. Every anten­na in the real world emits ener­gy in slight­ly uneven patterns. 

Still, RF engi­neers use a per­fect 0 dBi as a ref­er­ence point. As you go up in gain (the dBi goes from 0 to 1 to 3 to…13), the pat­tern becomes less and less globe-like and more focused in a sin­gle direc­tion & plane.

That brings us to EIRP, or Effec­tive Isotrop­ic Radi­at­ed Pow­er. This is a mea­sure of the radi­at­ed pow­er com­ing out of an anten­na in the direc­tion of its largest lobe. What’s a lobe? Let me show you:

Why is that max lobe ener­gy mea­sure of EIRP impor­tant? Because that’s what reg­u­la­to­ry agen­cies (like the FCC) use to mea­sure the pow­er com­ing out of an antenna. 

In the US on the 915 MHz fre­quen­cy we use, the FCC lim­it for EIRP is 36. You get the EIRP by adding the trans­mit­ted pow­er in dBm (what gets fed into the anten­na) to the anten­na gain in dBi.

Trans­mit­ted pow­er is mea­sured in dBm, or deci­bel mil­li­watts. The max trans­mit pow­er we can use in US Heli­um Hotspots is 30 dBm, or 1 watt. For Euros, the max trans­mit pow­er for uplinks is 14 dBm. You can read more on this here, in the LoRa docs. I’m US based, so we’ll stick with the US num­bers for this article.

The trans­mit­ter used in a US Heli­um Hotspot push­es out 27 dBm. The stock anten­na shipped with the orig­i­nal Heli­um Hotspot was a 3 dBi Anten­na gain. 

That gives us a total EIRP of 27 dBm + 3 dBi = 30 dBm

If you’re US based and do the math, you’re now real­iz­ing why a 9 dBi anten­na is the lim­it for your Heli­um Hotspot deploy­ments. 27 dBm + 9 dBi = 36 dBm, or the max allow­able EIRP

But wait, wait, wait, Nik. I thought this post was about cable loss? Why are we talk­ing about anten­nas and gain? Well, when you pass ener­gy through a cable, you lose some of it. Dif­fer­ent cables lose ener­gy at dif­fer­ent rates, usu­al­ly mea­sured as dB per dis­tance. In gen­er­al, thick­er cables lose less, and thin­ner cables lose more.

Cable loss effects EIRP, because remem­ber, EIRP is a mea­sure of what is “fed into the anten­na”. So:

EIRP = Trans­mit­ter pow­er (dBm) — Cable loss (dB) + Anten­na Gain (dBi)

This is why you can have a 9 dBi anten­na with lots of valid wit­ness­es if you have cable loss that brings your EIRP down to what Heli­um con­sid­ers “nor­mal” limits.

Before we get to the cable loss table, let’s cov­er one more term that gets thrown about, which is FSPL, or Free-Space Path Loss. This is the decrease (“atten­u­a­tion” for the RF nerds) in radio sig­nal pow­er over dis­tance. FSPL is impor­tant in Heli­um because it’s one of the fac­tors the blockchain uses to deter­mine if the sig­nal strength of any bea­con is “out of bounds”.

FSPL is used to com­bat gam­ing. If you’ve got 10 hotspots in your clos­et (remem­ber Modesto?), you can “say” they’re deployed in a per­fect grid pat­tern, but using FSPL to cal­cu­late the sig­nal strength that should be report­ed is one way to make sure they’re actu­al­ly, say, 800 meters apart and not all stacked on top of each other.

You can cal­cu­late FSPL here. Here’s what that might look like for 2 hotspots 50 km apart with clear line of sight, both using 3 dBi antennas:

How would you know if that’s with­in limits?

Let’s do this! Remem­ber that your hotspot pushed out 27 dBm. Let’s imag­ine you’re not using any cables, so cable loss is 0.

We’ve already account­ed for the gain using the cal­cu­la­tor, so we just sub­tract the FSPL from the trans­mit­ted pow­er (27 dBm — 119.4 dB) to get ‑92.4 dB.

That’s a sig­nal strength with­in nor­mal lim­its. For Heli­um hotspots in the US, most com­mon sig­nal strengths are (gen­er­al­ly) between ‑90 and ‑122, though it can go high­er or low­er, down to ‑130 in some instances. Now, there are some oth­er mea­sures, both pub­lic and pri­vate, that Heli­um uses to com­bat gam­ing when assess­ing a tx/rx receipt, but these are the basics.

So, with all that as back­ground, here’s your cable loss table. Use your trans­mit­ter pow­er minus the cable loss plus your anten­na gain to get your EIRP, and make sure that num­ber is 36 dBm or below.

You can get as detailed as you want, but I’d rec­om­mend not get­ting too wrapped up about your EIRP to the thou­sandth dBm. 

Length of CableLMR 195LMR 240LMR 400LMR 600LMR 900
5 Feet0.
20 Feet2.
50 Feet5.
75 Feet7.
100 Feet10.

Final­ly, one thing to think about is this: Hav­ing more pow­er come out of your anten­na isn’t always a good thing. An effec­tive way to plan your EIRP is to go after the LOWEST num­ber you think you can get away with, say, 30 or low­er. LoRa is already pret­ty darn capa­ble, so “extend­ing the range” with anten­na gain can be point­less. I mean, I’ve seen a 3 dBi anten­na be wit­nessed 200 km away. That anten­na does a way bet­ter job of hit­ting lots of local hotspots than a high­er gain would, in large part because of the effec­tive pat­tern it has. High­er dBi does­n’t always mean “use­ful longer range” (or greater HNT earn­ings). Just some­thing to think about.

Rock on!

References & Resources


148 responses to “Helium 101: Cable Loss and EIRP.”

  1. Nik:

    So I would be bet­ter off using my 5.8 dbi with LMR600? Hate to think of the cost of using LMR900

    Thanks for the help. Try­ing to get it cor­rect the first time so I’m not hav­ing to pay some­one to run up and down a tow­er to change out antennas. 

    Thanks for the reply.

  2. Hi Dar­ren, I’d run the calcs to see what your end out­put will be, then make the call from there re. anten­na gain & cable type/loss.

  3. Hi Nik,

    I recent­ly set up a Bob­cat Min­er and my SNR seems quite high. I failed to wit­ness anoth­er min­er ~3.3 km away but I am able to wit­ness one ~15 km away. Fun­ni­ly enough, (not real­ly though) as I was writ­ing this I failed anoth­er wit­ness to that same min­er. From what I have read, the invalids would be the result of the “anti-gam­ing” put into effect on the Heli­um Net­work since it falls out­side of the “accept­able range” for RSSI and SNR.

    I am com­plete­ly new to RF and though I have been read­ing, I am uncer­tain of the next steps to take. 

    My first thought was to increase the noise some­how so that it would low­er my SNR to an accept­able range. Is this pos­si­ble with an atten­u­a­tor maybe? 

    Sec­ond idea was to increase the sig­nal strength but I already have the anten­na mount­ed from my chim­ney run­ning through LMR 400 (53 ft) to light­ning arrestor to LMR 400 (10 ft) to min­er and am not sure putting it high­er would help con­sid­er­ing the fac­tor may be on the oth­er miner’s end. 

    Any input is great­ly appreciated. 

    Thank you.

    Distance~3.3 km
    Frequency903.9 MHz

    Distance~15 km
    Frequency904.7 MHz

    2nd Invalid
    Distance~3.3 km
    Frequency904.9 MHz

  4. Nik,

    I con­sis­tent­ly have Invalid Wit­ness­es with a few min­ers around me, when I wit­ness them or they wit­ness me. When this hap­pens the SNR is usu­al­ly a pos­i­tive val­ue but nev­er larg­er than 9db, most of the time its SNR 2–7db range but oth­er times they are valid. How can this be cor­rect­ed? (Exam­ples below)

    VALID (my Miner):
    High Mid­night Bobcat
    ~2.8 km
    904.9 MHz

    Colos­sal Fleece Dove
    ~2.8 km
    904.9 MHz

  5. Hi Jim, valid/invalid depends not only on your set­up but the set­up (and real­ly, gain) of those min­ers around you. If they have a high­er gain anten­na (and you do as well), there’s not much that’ll help until PoCv11 comes out.

  6. If I paid you $500 to con­sult for me, what could you do to improve my situation?
    1. I have a Gold RAK V2 on a 20 Foot flag pole with a 5.8 dbi antenna.
    2. I have .27 trans­mit scale with a total of 6 oth­er min­ers in hex.
    3. Cur­rent­ly 112 witnesses

    Do you think, look­ing at those para­me­ters, that you could improve my situation.

    My min­er:

  7. Prob­a­bly not much left to do there; you’ll need to find a bet­ter location.

  8. In the “lobe” image its clear that even an omni direc­tion­al anten­nae has a direc­tion. How do to tell where that direc­tion is? The rea­son I ask is I’m north­east of a large city. 99% of the min­ers are south­west or West of me. To the east there’s noth­ing. So it would make sense to align the pat­ter to face south­west. I have an 8dbi anten­na with light­ing arrestor (-.5 dbi) and 50′ of rfc400 cable (-2.1 dbi) at about 35′ feet high. Line of sight is good. I get valid wit­ness­es out to 50km. I’m think­ing the lobe direc­tion is cur­rent­ly fac­ing south­east based on my pat­tern of wit­ness but I don’t know how to offi­cial­ly tell.

  9. Hi Gary,
    The lobes in that image are for a sec­tor (direc­tion­al) anten­na. Every anten­na you pur­chase *should* have a dia­gram show­ing you the radi­a­tion pat­tern from a ver­ti­cal and hor­i­zon­tal per­spec­tive. Omni­di­rec­tion­al anten­nas do have dead spots, but they’re basi­cal­ly not worth pay­ing atten­tion to for Heli­um deploy­ments. An omni will “see” in all directions.

  10. […] you have a few options you can go for (the high­er the cost, the low­er the db loss). See here for a table of cable loss­es. I would typ­i­cal­ly go for LMR 400–600 cable as the best for price versus […]

  11. hi Nik. I have rac v2 min­er with 6dbi ante­naa, but cable neth is 90 feet (LMR400) is it nor­mal confg?
    Thank you

  12. That’s a pret­ty long cable, but with a 6 dBi anten­na should­n’t be an issue (depend­ing on where you are. US no prob­lem, Europe you’ll want to upgrade/shorten the cable.)

    Make sure you enter the loss cor­rect­ly there.

  13. Thanks to this and all the rest of your arti­cle I think I have a pret­ty good grasp on which anten­na and cable to use. Thanks!
    The one thing I’m won­der­ing. I cur­rent­ly have a 10 ft. Lmr-200 cable con­nect­ed to a 5.8dbi out­door anten­na. @5m height. My cur­rent fur­ther wit­ness is 18km. If I change out for 10ft. Of lmr-400 there would be less db loss and assum­ing Los I should be able to get more range? I’m not quite sure what less loss is actu­al­ly accomplishing

  14. Aaron Olson Avatar
    Aaron Olson
  15. Mark S Werner Avatar
    Mark S Werner

    I think this ques­tion is answered… It want to be sure. 

    I have an hnten­na 3dbi out­door con­nect­ed with 20 ft of lmr240. Looks like loss is 1.5. Should I include the loss in the Heli­um app to account for the loss?

  16. Yep, include the loss from the cable.

  17. Jared Holm Avatar
    Jared Holm

    Does cable loss change the focus of a high­er dB anten­na? i.e. Would a 9dB anten­na that would have a flat focused plane be changed into a wider focused plane (as in your dia­gram on anten­na gain) if it had a 4 dB loss form a 100′ run of LMR400? Or is that not how it works?

    I am in FL with VERY flat topog­ra­phy (includ­ing buildings…it’s essen­tial­ly wide open space above the trees), but am under the tree canopy. I have the fun but dif­fi­cult task of try­ing to posi­tion an anten­na above the canopy where it should be able to “see” for miles. By my cur­rent under­stand­ing, I feel I need some­thing like a 7 dB anten­na up on 100′ of LMR400 above the canopy, but am curi­ous if I’ll have a flat plane shoot­ing over everyone.

    Thanks for all the awe­some info!

  18. Hi Jared, it won’t change the pat­tern, it’ll just weak­en the out­put along that pattern.

  19. Nate Martin Avatar
    Nate Martin

    New Bob­cat arriv­ing in a few days. Locat­ed in between Phoenix & Tuc­son, just a few min­ers near­by, but have option to also place clos­er to City as need­ed; can you please email me with infor­ma­tion regard­ing con­sul­ta­tion for my set­up & strategy?

  20. Abner Silverio Avatar
    Abner Silverio

    HI bud­dy, how would you go about reduc­ing the trans­mit gain? If you found u are run­ning high­er then you should and set­up in the heli­um app to a 15dbi anten­na and still was too high what can you put in the line to reduce the trans­mit gain?

  21. What anten­na are you run­ning? That’d be where I’d start. 🙂

  22. Hi,
    I’ve read through the arti­cle and embar­rassed to say still stumped… I’ve got a 5.8dbi anten­na on a 10m long LMR400 cable with a light­ning arrestor between the aer­i­al and cable. Is the fig­ure I put into the heli­um app sim­ply 5.8 less the loss in the cable which I think = 4.4dbi

    Any help would be real­ly appre­ci­at­ed thank you!

    All the best


  23. Yep, bang on. [Anten­na gain] — [cable loss] — [inser­tion loss from light­ning arrestor] = Assert­ed gain in app.

  24. I live in the sub­urbs on a hill and have an anten­na on top of my roof about 40~ feet above ground. I am run­ning 40ft of LMR400, which comes down to about 1.57db of loss. I used to run a 5.8db anten­na when I had near 0 loss. Would it be more ben­e­fi­cial to swap to a 8dbi anten­na due to the loss intro­duced with the new cable?

  25. Prob­a­bly not, I’d stick with the 5.8. Focus on keep­ing the anten­na up high and you’ll be get­ting the most benefit.

  26. hi Nik, how are you — great post! 

    I am try­ing to fig­ure out my best set­up. I have heli­um min­er (bob­cat 300) with the stock anten­na on my roof. my house is prob 180m above sea lev­el +10 meters for the anten­na. most of the anten­nas i want to hear /see are below me or very far away (clos­est is 4km) . I actu­al­ly think that I have to gain from a high gain anten­na (8dbi is prob the sweet spot + 20 feet of cable + a light­ing protector.)


    does a high gain 8 or 10 sound too much? or a 6.5 better?

  27. my fav part of this arti­cle is how GK says ‘i’m show­ing you how to do the math your­self!’ and all the com­ments are like ‘what about my set­up, it’s like this:’ Thanks for the info, way to always make it digestible

  28. 6.5 to 8 is prob­a­bly fine.

  29. @nik ty very much — appre­ci­ate all your “guardian angel like approach” — i went with 8 to try and reach the remote islands 🙂

    @tanner you are right 🙂 but as to myself and in my defense there are com­po­nents implied in the dis­tance and height which make the deci­sion a lit­tle more “expe­ri­ence” based vs math based. I liked this cal­cu­la­tor also https://www.pasternack.com/t‑calculator-antenna-downtilt.aspx — it helps under­stand how the height and dis­tance play into it as well as the ver­ti­cal lobe degrees


  30. I messed up and ordered a LMR600 cable with the wrong con­nec­tor. Will using a female to female con­vert­er result in a big lose? Is it worth replac­ing the cable or would it not make much difference?

  31. Depends on the con­nec­tor qual­i­ty; any­thing you use should list its “inser­tion loss”. Prob­a­bly not a huge deal, though if you’re run­ning LMR600 you prob­a­bly have a rea­son to avoid loss. 😉

  32. Hey NIK, is it worth run­ing 25 met­ter cable in order to climb anten­na to roof of my 45metter build­ing and com­plet­ly open the view in full 360 cir­cle? Or should I rather have around 150 degree open view and stay much low­er but run short cable. Also which cable would you sug­gest for such a long set­up? Is LDF 7/8 okay or should I stick to LMR — 600 or some­thing else? Thank you for the answer in advance.

  33. I’d say get­ting it high off­sets any cable loss issues. Cal­cu­late cable loss for your length & fre­quen­cy and decide on your cable choice from there.

  34. I already did, but I am not sure how much loss is a red flag? Is 2 db loss accept­able for 8–9 dbi anten­na? I am from Europe btw.
    I saw that every­one just talk­ing about LMR-400 as a stan­dard and LMR-600 for longer set ups. So not sure if LDF cables are okay for hnt min­ing usage because no one is men­tion­ing them even with the fact they got low­er db lost.

  35. 2 dB loss should be fine. I’m not famil­iar with LDF, sor­ry mate!

  36. Hey Nik — Thanks for this awe­some post — When you change the gain in Heli­um, this will only affect the Tx, not the Rx, cor­rect? Say you have a 15dB anten­na, if you set it to 15 in Heli­um, the Tx will be brought down to 36 (USA) while the Rx will remain at 42. Am I under­stand­ing this right?

  37. Yep, that’s cor­rect. Whew, that’ll be a tight pattern!

  38. Haha thanks! I’m not actu­al­ly using a 15dBi — I was just using it as an exag­ger­at­ed exam­ple. I run a 10dBi anten­na and I’m plan­ning to install a 2‑way ampli­fi­er with a SAW fil­ter on it and I want to make sure I’m in the legal range for my Tx with­out los­ing any Rx. Thanks again for all of your work in teach­ing us every­thing you know!

    Actu­al­ly while I have you on the line — do you know if the Bob­cat puts out 25dBi or 27dBi? I know the max for the US is 27 but most of what I can find in forums says Bob­cat puts out 25.

  39. HI Nik,

    First what an amaz­ing arti­cle, I’ve read hun­dreds and by far this is the most comprehensive. 

    I’ve just set­up my Bob­cat Min­er, live in Scot­land in U.K. How­ev­er, I messed up with ini­tial set­up, I got conned on some cable. 

    So my set­up is bob­cat 300, McGill 6DBI tuned anten­na, I’m 63M above sea lev­el and my anten­na is 13m high (top of house). How­ev­er, I have 15 metres of RG58 cable (I know right). I cal­cu­lat­ed the loss it’s over 6dbi so I’m not sure why I am see­ing wit­ness­es 24km away. I’m gen­er­at­ing around .4HNT per day but only 5 witnesses/2 becons a day….. In 3 days time I am replac­ing the cable to 10 Metres LMR 600 (£100 just for the cable), once I set­up I’m going to update Heli­um app with a .4dbi loss is that cor­rect? So new anten­na will be 5.6DBI. I’m more keen to see what impact it will have with the new cable? What’s your thoughts? Hope­ful­ly I’ll have more witnesses. 

    I’ll update you on the results hope­ful­ly the upgrade of the new cable will pay for itself and show the results.

  40. Right on Ben. You may have more wit­ness­es if the extra sig­nal gets you through a few more walls/trees. Depends on how many Hotspots are around you. .4 HNT/day right now is about 4x glob­al average. 🙂

  41. M Dave Avatar
    M Dave

    Hi nik, How to cal­cu­late db , dbi, Eire for min­er using 860 to 870:mhz…pls advice which anten­na should I use.

  42. Hey mug, fol­low the links in this arti­cle and you can run the calcs. Also, check out this arti­cle on choos­ing anten­nas.

  43. Hey, I recent­ly upgrad­ed from a stock ante­na to 7.5 dbi McGill and I have some invalids (rssi too high) when I am wit­ness­ing. My first thought was to try putting a high­er num­ber of dbi into the app but if I am cor­rect that would just weak­en my tx and not rx. I am run­ing a 15m of lmr 600 + a light­ning arestor. Do you have any idea beside atten­u­a­tor or you think I have to buy attenuator?
    Thank you in advance

  44. Hmm, how long has it been? I might give it a few more days and let this whole Light Hotspots thing set­tle before I made any changes.

  45. Raghav Avatar

    I’ve a 6 Dbi anten­na at the height of 15 meter. My Anten­na is Con­nect­ed with 12meter long LMR 400 Cable going through a 0.5 meter long RG316 Jumper(connector).
    What anten­na gain should I men­tion on Heli­um App

  46. Hi Raghav, add up all the loss­es from your cables and sub­tract that from the anten­na gain. I’d prob­a­bly include .2 dB per con­nec­tor, but that’s split­ting hairs for this.

  47. First off thanks for respond­ing to peo­ple. So here is the ques­tion. 5.8 anten­na > arrestor > 25ft LMR240 > Min­er. I want to add a amp (RX Gain +12dB,TX Gain +3dB, 2 saw fil­ters) would it be bet­ter to add it near the min­er or antenna…maybe not at all?

  48. Amp not need­ed. I’m not sure about best posi­tion­ing on it re. where in the chain, a quick search sug­gests clos­est to the anten­na, but again, I’m not sure.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.