Heltec HT-M2808 RSSI sensitivity

As somebody that has 19 of these on order this is very worrying!

Hopefully Heltec can investigate this quickly and come up with a patch to resolve the issue!


Unfortunately I haven’t heard back from heltec yet. They said they were investigating so I guess we have to wait bit more.

Someone else told me that heltec said that their RSSI calculation is different from other brands like Sensecap. This will be a BIG issue when PoCv11 kicks in as this would invalidate almost all witnesses in the current state(meaning 0 income).

There is clear evidence that there are issues that need to be resolved.

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Same issue for me. Only low RSSI beacons. Are Heltec gonna do anything about it? Or we will have low performance hotspots?

Same, not a single witness below RSSI -107, while around me people do witness these;

I am in exactly the same boat with all 5 of my heltec!!!

Surely heltec can make a patch in the firmware for this!! I had 5 Nebra and swapped them out for heltec!!! My Nebra were getting me 1.5 HNT a day, due to the update issues and emmc I swapped all of my setup for heltec! I hope they can fix this with firmware!!!

I receive some beacons with -105 dBm, however they are only 1/3 of beacons comparing activity of my hotspot with other SenseCAP hotspot that is to 600 meters next to me on worst condition. My neighbor SenseCAP hotspot is receiving the beacons with RSSI -110-120 dBm. I elevated my hotspot 5 meters, I changed my antenna 3 dBi by other 5 dBi. I am getting 105 witnesses/5 days, they are receiving my beacons perfectly, but I don’t do it so well.

I am in the exact same position and can show you a snapshot of my Lora logs. I have 5 heltec with the same issue!!! Surely it isn’t a small batch of four as you guys said!

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This is not an isolated issue and affects a number of hotspots. I am also having the same issue. With the same location and antenna, I swapped this with a bobcat and my witnessing got reduced to only 3-4 per day from more than 25.

More data.


I have the same problem with 6 of my heltec!!! This is not acceptable, please somebody fill a form and ask helium community to take action.

Hello from The Netherlands, I want to buy a Heltec Miner, but have some concerns after reading on this forum.

I also see that Heltec is performing tests a week ago.
Can somebody from Heltec please update us with a formal statement on the issues and their progress to solve this issue? Thanks in advance!

Tagging @Supporter please update us!

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Since @Supporter @Mikmac can’t seem to be bothered to reply to my messages on discord, email and this forum it might be time to share this issue with a wider audience on Reddit and other communities. It’s not something that I want to do, but being ignored by the manufacturer on a serious issue after spending a lot of time on the subject isn’t nice.

Don’t buy a heltec for now. It is a gamble if your unit will be OK and so far we identified a lot of bad performing units. Better buy a Sensecap for 2x or 3x the price on eBay as you will earn that back quicker.

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Hi, I’m noticing that my Heltec hotspot is underperforming as well. I sincerely hope that Heltec support will examine these issues with the highest priority possible.

I compared my Heltec hotspot with my 2 most nearby hotspots (non-heltec, I think RAK) and I can see that these are 4 to 5 times better performing in witnessing/beacons and therefor as well HTN earnings.
Those other hotspots live like 400-600m from my location, same landscape (flat no high buildings), same setup height (checked myself visually), same dBi antenna.

When I use the helium.hiker website to compare the hotspots last 3 days of witnessed beacons indepth, I can see that my heltec operates from -58dBm to -115dBm RSSI. But the 2 neighbouring hotspots both work from -53dBm to -121dBm RSSI.
So it seems very clear that I’m missing quiet some beacons between -115 and -121, a rough estimate is like 40-60% missing.

Looking at the lora logfile of my heltec I can see that in a time frame of 2.5h I have received 22 beacons (data size 52) all valid SNR/RSSI values (Pocv10), but this result only in 3 registered witnesses.
The other 2 compared hotspots have 10+ registered witnessed in that same time frame.

If more info and/or logfiles are needed, feel free to reply or contact me.

Thank everyone for your feedback all the time. We attach great importance to this issue. Our R&D team has done a lot of experiments and tests on this issue.

We purchased LoRa gateway modules produced by other manufacturers and used the same LoRa end node to send data.

  1. Extreme communication test

The LoRa gateway side used the same antenna and conducted a comparison test at the same location.

We put the LoRa node in another office (separate a wall), and gradually increase the attenuator, when the attenuator value increases to 100dB

Whether HT-M2808 or the LoRa gateway module produced by other manufacturers, All alternately produced situations where the signal could be received by chance. It shows that the limit value has been reached.

Conclusion: It shows that the limit communication distance is similar. But it shows a different RSSI value.

  1. The impact of different antennas on RSSI

The LoRa gateway part is connected to a cheap, low-gain spring antenna, and the attenuator of the node remains unchanged, and the distance is closer to the LoRa gateway (because the gain of the antenna is reduced, the distance is reduced to ensure that the gateway can receive data more easily. Observe the RSSI data).

It can be seen that whether it is the HT-M2808 or the LoRa gateway module produced by other manufacturers, the lowest RSSI value has become larger.

Conclusion: The antenna and coaxial cable will affect the RSSI value.

  1. Remove the antenna at the same time

At the same time, the antenna is removed from the LoRa gateway, and a 60dB attenuator is added to the LoRa node. The node is very close to the gateway, almost next to the gateway.

Whether it is the HT-M2808 or the LoRa gateway module produced by other manufacturers, the following figure is a comparison of the minimum RSSI (difference within 5dB).

In a real communication situation, an antenna is necessary, otherwise it may cause permanent damage to the radio frequency circuit. The removal of the antenna here is only a short-term experimental need.

Conclusion: The results of experiment 2 be verified again; on the other hand, it can be explained that the lower RSSI of the gateway module does not mean that it can receive longer distances. It can only be explained as different manufacturers. In the same communication scenario, RSSI Behave as different values.

But under the same circumstances, why some HT-M2808’s RSSI higher?

  1. The influence from the antenna and the coaxial wire, the attenuation of the antenna coaxial wire, the sensitivity of the antenna, the center frequency of the antenna, impedance matching and other conditions may affect the value of RSSI;

  2. The LoRa baseband chipset used by HT-M2808 is SX1308+SX1257. The circuit is designed according to Semtech’s reference design. The FEM chip is SE2435L, and the FEM chip of the SX1302 reference design circuit is SKY66420.

The gain of SE2435L is 14~18dB (typical value is 16dB).

While the gain of SKY66420 is 18dB.

I believe that the data in the SKYWORKS data sheet is the conclusion after a lot of experimental verification. When the HT-M2808 handles the FEM gain, it is calculated according to the typical value of 16dB. In fact, the FEM gain at this time may be 14dB or 18dB. This causes the difference in the minimum RSSI.

But the trouble is that the difference is not a fixed value. In response to this problem, we are discussing if we need to release a patch, allow users can choose in the dashboard depending on their own situation whether to use the algorithm to correct the difference caused by FEM.

Main points of disagreement:

  1. The important thing is that the communication distance is similar, and the RSSI value does not affect anything;
  2. This patch will be friendly to cheating users;
  3. Just refer to the two Heltec Indoor hotspot reports by @fantasy2 via email (considered as the problem with receiving sensitivity), indeed the HNT earn are crazy high! Further proved that it does not affect the income.

In the future, we will optimize the hardware circuit to solve the difference in FEM gain.

We did not ignore this issue. On the contrary, after receiving such feedback, we have been actively following up on this matter. It took some time to wait for samples from other manufacturers and to do related tests and experiments, which led to the slow response.

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We don’t want to know about the future. What are you doing about the present problem?

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Thanks @Supporter for your intensive reply. I like to recap your information, could you confirm if I understand well?

-When the new batch is modified, are the units ordered last week modified when they are shipped?

-Which of the putty session is the Heltec ( and the LoraNode?

-Your test compared the RSSI levels of both nodes. The RSSI levels are a parameter in the PoC protocol, and they seems to be relevant to be 100% accurate? With you’re labsetup you show us that the Heltec unit is showing a louder (closer to 0) RSSI value. Which means we should be hitting the green POCv10 area more with heltec compared to other vendors? The opposite we see, lot of users are complaining about the bad earnings of heltec miners. Could you elaborate?

-Regarding to gain, is there any way you can test malformed data transmission in your lab? With a high gain its also possible you oversteer the RX circuit? Where datapackets in the lower levels <100dBm where unable to detect, due to the oversteer.

-With the patch you mentioned user can select a gain between 14-18dBm? A higher gain from 16 (current) compared to 18 (patch) should give higher RSSI values closer to 0 (e.a -119 with 16db gain, will become -117dbm with 18db gain)

-are you sure the gain is enable in software? If I noticed the -132 on the loranode and compared to your heltec node, its about 15dBm difference?


Please note LoraWAN could reach -135dBm levels

Heltec Indoor Hotspot (HT-2808) main attributes:
Main hardware
CPU: Quad-core Cortex-A53 64-bit 1.5GHz;
ROM: 32G eMMC 5.1;
LoRa baseband: SX1308 + SX1255/7 chipset.


Up to -139dBm sensitivity with SX1257 or SX1255 Tx/Rx front-end

RSSI levels LoraWan is able to go deep as -135dBm

Illustration what I mentioned above, a higher RSSI should give you more valid PoC results. And higher earnings.

@fantasy2 are you’re screenshots the default stock nodes? I don’t believe this earnings, can we show 10 of this good working miners from Heltec?