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Can I Get A Witness?

Hav­ing trou­ble under­stand­ing why your hotspot isn’t get­ting a Wit­ness? Are you see­ing mes­sages about being above or below the bounds of an RSSI met­ric? Let’s dig in!

We’ll start with this, the infa­mous PoC V10 SNR lim­its graphic:

I’ll explain the X and Y axis in a bit, but at first glace it’s pret­ty basic. 

Green = Good, Red (pink?) = Bad. Find the num­bers report­ed for your spe­cif­ic Wit­ness event, see where they inter­sect, and you’ll know why you have an Invalid wit­ness. Yes, yes, yes, if you’re a “radio head” you instant­ly see some­thing wrong, but for now let’s keep it simple.

We’ll go through two exam­ples; 1 invalid, and 1 valid. Here’s an invalid witness.

Three things are listed: 

  • The dis­tance in meters. This is used to cal­cu­late FSPL, or Free Space Path Loss. More on that in a sec.
  • The sig­nal strength in dBm (RSSI)
  • The lev­el of sig­nal above the noise floor, in dB. (SNR)

Here’s how that wit­ness charts out:

With a high SNR (any­thing above 0 is high for Heli­um), at only 914 meters this sig­nal is basi­cal­ly too good for the distance.

Ok, so what does it look like if the wit­ness is valid?

We’re look­ing at the same three things, but now we’re at about twice the dis­tance, and if you remem­ber your dB strength rules (every 3 dou­bles or halves), about a quar­ter of the SNR.

Easy enough to read a chart, right? But what does it mean, and how can you get more valid witnesses?

We’ll start by defin­ing two things first: RSSI and SNR.

RSSI = Received Sig­nal Strength Indi­ca­tor. In very sim­ple terms, RSSI mea­sures the strength of the radio sig­nal you’re receiving. 

In RSSI mea­sure­ments, the larg­er the neg­a­tive num­ber, the weak­er the sig­nal. ‑130 is weak­er than ‑100. In gen­er­al, in the land of Heli­um, you want your RSSI to be between ‑82 and ‑134.

SNR = Sig­nal to Noise Ratio. This is a mea­sure of the qual­i­ty of a sig­nal com­pared to the back­ground radio “noise”. It’s expressed in terms of dB (deci­bels), and the big­ger the num­ber, the bet­ter. Except when it’s not.

Wait, a sig­nal can be too good? Yep. 

When Heli­um start­ed (and basi­cal­ly, up until the present, August 2021), Heli­um had a prob­lem: They were sell­ing radio devices. Why is that a prob­lem? This’ll get more com­pli­cat­ed before it gets sim­ple, so buck­le up and pay attention.

Every­one (in the US, and in most coun­tries) sell­ing a radio device has to have it cer­ti­fied by some nation­al body. In the US, that body is the FCC. One of the things they check dur­ing cer­ti­fi­ca­tion is that your device does­n’t break any emis­sion-strength rules (tech­ni­cal­ly EIRP, more on that here.)

Heli­um is required to stay with­in the lim­its of the rules. To do that, they used a low gain anten­na (1.8 dBi gain) and a rea­son­able amount of ener­gy out­put (-27 dBm). That put them at ‑28.8 dBi for max EIRP, well with­in the lim­its for the US, which is a max EIRP of ‑36 dBi. 

The FCC also requires a man­u­fac­tur­er to build units that “pre­vent” the con­sumer from chang­ing the anten­na. Heli­um accom­plished this by using RP-SMA con­nec­tions. Yep, that counts as pre­ven­tion. It’s an out­dat­ed sys­tem, for sure.

An addi­tion­al mea­sure tak­en to ensure there was no encour­age­ment to “improve” your anten­na (and even they acknowl­edge it isn’t a great one) is to set fair­ly strict and some­times unrea­son­able rules regard­ing what a received radio sig­nal should be in terms of the sig­nal strength and quality.

This is accom­plished in part by mea­sur­ing ALL anten­nas (even your high gain fan­cy wazoo anten­nas) AS IF THEY WERE THE HELIUM STOCK ANTENNA.

No, that does­n’t make sense. Yes, it was rea­son­able at the time. Yes, it will be changed. 

How did Heli­um come up with those rules, and why? I’ll start with the Why: To stop cheaters, also known as “gamers” because they game the sys­tem with­out pro­vid­ing any actu­al benefit.

Cheaters used to be able to just plug in a bunch of hotspots stacked on top of each oth­er. Those hotspots would wit­ness each oth­er from inch­es away while report­ing false­ly assert­ed loca­tions that made them seem to be much fur­ther apart. It appeared they were pro­vid­ing great cov­er­age. So they earned. Mas­sive­ly earned. 

One of the most egre­gious exam­ples hap­pened in a lit­tle town called Modesto, in Cal­i­for­nia. At the peak of the cheat­ing, in late sum­mer 2020, a group of hotspots (prob­a­bly in a clos­et, and not even in Modesto) were earn­ing thou­sands of HNT per day. Yes, per day. 

Heli­um has since worked to com­bat gam­ing in more and more nuanced ways, but the way they approached Modesto was with a giant radio-sig­nal mea­sur­ing ham­mer: The RSSI/SNR chart. This was cre­at­ed by a Heli­um employ­ee who ana­lyzed almost half a mil­lion PoC receipts and looked for out­lier results. 

He was approach­ing this in clas­sic Sil­i­con Val­ley fash­ion: Look at the actu­al dataset, don’t rely on “old” thought, and fig­ure out a new way to do a bet­ter job. Admirable, but it turned out to penal­ize not only egre­gious gamers, but many of the rest of us who just want­ed to do an above aver­age job.

The Modesto clus­ter was gut­ted, but the RSSI/SNR chart stayed in place. Oth­er changes (HIP 15 & 17) entered into the sys­tem and incen­tivized spread­ing out and being reward­ed for pro­vid­ing bet­ter and bet­ter cov­er­age, but the RSSI/SNR chart stayed.

It was­n’t because the Heli­um team was ignor­ing it. They had much a big­ger chal­lenge to sur­mount: Get­ting Val­ida­tors online so the blockchain could stop suf­fo­cat­ing itself. With that mis­sion-crit­i­cal task accom­plished, they can now (summer/late sum­mer 2021) turn to mak­ing sure the blockchain improves in accu­rate­ly reward­ing superb coverage.

Which brings us, almost, to today, some­time in August of 2021. With PoCv11 (Proof of Cov­er­age Ver­sion 11) on the hori­zon, we’re about to take a strong step in the direc­tion of reward­ing strong & clear sig­nal cov­er­age over short and long distances. 

As you’re see­ing in the app, Heli­um is offer­ing you the chance to enter your anten­na gain and ele­va­tion. This will help them more accu­rate­ly assess whether or not your wit­ness­es are valid. As of today (Aug 4th, 2021), those two met­rics don’t actu­al­ly make a dif­fer­ence for you, the hotspot own­er, but…they will.

In the future, when PoCv11 comes online, the details you enter will be applied to your wit­ness receipts. In order to com­bat gam­ing (essen­tial­ly to stop every­one from just say­ing they have a 50 dBi gain anten­na so all of their wit­ness­es are good), Heli­um will simul­ta­ne­ous­ly apply your gain AND decrease your trans­mit strength. That’s fair, by the way, and you should want that to happen. 

I know, I know. Nobody likes decreased strength. Trust me on this one: LoRa already gives you TONS of range. Your goal is not long range, it’s increased earn­ings, and earn­ings come from valid wit­ness receipts. 

What will that look like? Full details over here, but for those of you who aren’t deep into radio geek­ery, the big pic­ture is that Heli­um will drop SNR and just use RSSI and dis­tance. Here’s a pro­posed chart. Meters on the Y axis, RSSI on the X axis.

Ok, so you’ve got three lines on there: Red, Yel­low, Green. The lines rep­re­sent the cur­rent cut­off (Red) for a valid wit­ness as well as pro­posed future cut­offs (Yel­low and Green). 

You’re also see­ing a bunch of blue dots. Those blue dots rep­re­sent report­ed wit­ness met­rics of RSSI at some dis­tance. The green line is the most restric­tive, but is based on actu­al val­ues of RSSI at some giv­en dis­tance, which is far more accu­rate than the cur­rent RSSI/SNR curve.

To keep it sim­ple, this means that in the future, when PoCv11 replaces the cur­rent ver­sion, a hotspot using a non-stock anten­na will not be penal­ized for it. Whether the yel­low, or green, or some oth­er line is used is still up for debate. 

We’ll wrap this up with one of the most impor­tant take­aways: What anten­na will help you stay with­in the pro­posed lim­its? Easy: It’s the LOWEST gain anten­na you can use. See how the curves all shoot up at a fair­ly defined RSSI? That’s the key. If your RSSI is even a few points “to the left”, you can be on the wrong side of the line. 

This helps explain why in many cas­es, when you get that fan­cy super high gain anten­na, your valid wit­ness­es dis­ap­pear. So what anten­na should you buy?

My rec­om­men­da­tion is still the HNTen­na, but any of the low gain (4 or less) anten­nas in your coun­tries fre­quen­cy, from a wide vari­ety of sources like McGill, Par­ley Labs, L‑com, or Laird will be fine.

If you’re will­ing to explore your inner geek and you like to tin­ker, take a look at atten­u­a­tors. They’ll atten­u­ate (or weak­en) the sig­nal (both tx & rx), but they’ll also increase the SNR, so exper­i­ment cau­tious­ly. Here are a few options:

Expen­sive (~$400) and unnec­es­sary, but hey, if you want a great unit — Fairview 0–11 dB Step Attenuator

Cheap­er ($25), less pre­cise with­out extra mea­sur­ing equip­ment — ATM RF Vari­able Atten­u­a­tor AF033-10 DC-1000 MHz 50 Ohm

An atten­u­a­tor decreas­es your sig­nal strength both ways. They’re not a great long term option. The best option is to use a low gain anten­na and get it up high in the right loca­tion. If you see that the Near­son 9 or RAK 8 that you bought when you were in “Big­ger is bet­ter” mode gets more valid wit­ness­es once you’ve tak­en a lit­tle sauce out of it, well, you’ll have some use­ful data points (that I’d love to hear about.)

Want to go deep­er? Con­sid­er hir­ing me to help you out; I love help­ing peo­ple crush with Helium.

Hap­py Witnessing!

**This post was writ­ten with tech­ni­cal over­sight from @jerm on Dis­cord. He is an absolute wiz­ard with this. All right­eous accu­ra­cy is his, any errors are mine. ‑Nik@GKI

65 thoughts on “Can I Get A Witness?”

  1. Hey Nik,

    I had a quick ques­tion, in my coun­try the max dbm is 20 for the 868 band. What is the max trans­mit pow­er for a Sense­cap M1 EU868 hotspot — all I can find is “up to 26dbm”. I have a 6dbi anten­na and am run­ning a 33 feet cable, would it be bet­ter to use LMR 195 (with a loss of 4dbi) or a LMR 400 cable (with a loss of 1.4dbi) to reduce the gain to an accept­able lev­el? I am a bit con­fused as to how I will be impact­ed if my gain is too high as I don’t have access to any low gain anten­nas here. Any help would be great! thanks so much

  2. Hey Nik,
    Is there an effec­tive way you can degrade the SNR val­ue. In my neigh­bor­hood, a new min­er has popped up and I’m get­ting invalid wit­ness­es from them. I feel if i can low­er the SNR val­ue of the received sig­nal just slight­ly, I’ll be able to get a valid wit­ness from them. 

    I don’t want to have to move my min­er or any­thing, just look­ing for a way to low­er the SNR a few points.

    Thoughts?

  3. Hi James, there are tech­ni­cal ways you can degrade sig­nal strength/quality, but you’re best off focus­ing on wit­ness­ing lots of min­ers and not wor­ry­ing about 1 close by. Heli­um is all about pro­vid­ing WUPU cov­er­age; one near­by min­er won’t make any dif­fer­ence to that.

  4. My rssi when I did dis­cov­ery was ‑16.
    How do I dum­my my sig­nal strength
    On the oth­er end I am get­ting too much noise
    ‑10 to ‑13 is this because of my strong sig­nal strength pick­ing every­thing up

  5. Hi Chris, what anten­na do you have, and what anten­na do the hotspots on the oth­er end have? I’d start with a low gain or stock antenna.

  6. Hi Nik, thanks for the input as always!

    I keep check­ing out the HNTen­na and am ready to pull the trig­ger .. but, even with my stock 2.6 db I’m get­ting Invalid Wit­ness­es that are between 850m — 450m because for those the SNR is around 10 db. Basi­cal­ly any­one in the same Hex usu­al­ly is invalid. I seem to blow them away prob­a­bly because I have great place­ment way up over the roof.

    Before tin­ker­ing any­more — I won­der if I should wait to see how the pocv11 update affects this. 

    Do you think the pocv11 update might solve the overblown SNR for close hotspots and cure the Invalid Witnesses?

    Thanks!

    (on a side note I’m stoked as my 2nd Sense­cap comes today to be set up at my folks house)

  7. Hi Adam, the PoCv11 update will solve the SNR issues because it won’t rely on SNR. 🙂 You could hold off on buy­ing the HNTen­na if you want. For close wit­ness­es with high gain anten­nas, there’s not much you can do.

  8. Jasper van Berkel

    Good­morn­ing, after­noon or evening Nik,

    Thanks for the arti­cle; it’s pret­ty dif­fi­cult to find clear info on this, espe­cial­ly for non savvy tech boys and girls like myself. I’ll have to read through it a few extra times though to real­ly under­stand all of it 😉 There are two sit­u­a­tions I hope you can help me out with, and can pro­vide me and oth­er read­ers with some advice.

    I’ve got one Sense­Cap M1 in the mid­dle of Ams­ter­dam; the most min­er-occu­pied hexagon/area’s of The Nether­lands prob­a­bly, and set it up with a 6.5 dBi anten­na (LMR400 5 meters) and 20 meters high up. I’m won­der­ing if this is the right set up, or that I should go for let’s say a 3 dBi antenne instead?

    On the oth­er hand I have a Nebra min­er at home (10dBi / 10 meters up / LMR400 5 meters) and this is in a rur­al area; I have the only min­er in the near­by area. How would you set up this loca­tion, as this is a exact oppo­site sit­u­a­tion as I have in Ams­ter­dam? Am I good or should I prob­a­bly change the antenna?

    Thanks in advance!

    Kind regards,
    Jasper

  9. Hi Jasper, both of those sound rea­son­able, although the 10 dBi is def­i­nite­ly on the high end of things. Your earn­ings are far more affect­ed by your loca­tion than your anten­na set­up. In both cas­es I’d opt for a low­er gain anten­na, but it prob­a­bly won’t make a big difference.

  10. I rotat­ed between a 1.2DBI Stock Sense­cap anten­na, 5.8dbi after­mar­ket and 8dbi after­mar­ket anten­na and it real­ly does not impact much in my area of NYC.

    1.2dbi had 571 hotspots respond­ed dur­ing dis­cov­ery mode — Earn­ings were about .23 avg/day first 14 days
    5.8 dbi had 645 hotspots respond­ed dur­ing dis­cov­ery mode — Earn­ings were about .21avg/day last 14 days
    8dbi had 596 hotspots respond­ed dur­ing dis­cov­ery mode — Earn­ings were .18avg/day mid 14 days

    I know there are so many vari­ables that impact earn­ings. Roll­outs, updates, added hotspots, etc but it does­n’t seem like it mat­ters what type of anten­na is being used where I am liv­ing in the heart of NYC. There are 50 hotspots in my Hex and I have a trans­mit score of .01. I did the same exer­cise in anoth­er Hex with a .2 trans­mit score and same results.. The anten­na changes are sub-optimal.

    Loca­tion and posi­tion­ing is key like NIK has been say­ing.. I do have one in a sub­ur­ban area where it is on a pret­ty big Lake. Oth­ers around me have been get­ting 15–20 HNT per month where I am earn­ing 7.5 per month. I have rotat­ed between dif­fer­ent anten­na but not too suc­cess­ful. Not sure on that one.

  11. Hi Jonathan,
    That sounds about right. NYC is pret­ty much the worst place to deploy a hotspot; just way too many of ’em there already. A main key to earn­ings is line of sight to oth­er un-scaled hotspots.

  12. Hi Nik! I just put an 6.5dbi Mikrotik anten­na on my roof, wired with 12m rg58 cable to the Bob­cat min­er. My ques­tion is — after the cable loss, is the anten­na work­ing like 1.5 low dbi with big angle of spread­ing or still spread like 30 degrees ‚but low range.
    I’m ask­ing, because in the dis­cov­ery mode i catch just 20% of the hotspots com­pared with stock 4dbi indoor anten­na. If you have any sug­ges­tions it will be great.
    This blog is one of the most use­ful ones , that i find out ! Best regards!

  13. Hi Atanas, an anten­na will radi­ate out at the same pat­tern no mat­ter how much loss you have, just with dif­fer­ent lev­els of power/range. While not total­ly tech­ni­cal­ly accu­rate, that’s close enough to be useful. 🙂

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