HELTEC LoRA V4 issues

Help & Support
1

Hello,

I’m using Heltec V3 (V3.2) modules to remotely control devices.
Everything works perfectly.

I was thinking of upgrading to V4 modules to increase the range.

Indeed, version 4 modules are known for providing more power, and consequently, a greater range.

However, I’m still hesitant about these V4 modules. Let me explain:

I should mention that my tests are done on my desk.

The transmitter is a maximum of 2 meters from the receivers.

So,

  • One V3 module emits a repetitive signal at its maximum power.

  • Opposite it, I have two receivers, one V3 and one V4, with exactly the same code.

The V3 displays an RSSI of approximately 33dBm, while the V4 displays -96dBm!

The V3 is 10 cm from the V4. Same code, same antenna, same power supply… I’m testing another V4 module. Same result.

Strange, isn’t it? How can such a difference be explained?

I’m going a little further with my test. This time, I’m using one of the two V4 modules as a transmitter.

For reception, I’m not changing anything; I’m still using a V3 and a V4. Identical results!

Both V4 modules I have are working.

So, I’m wondering if this commercially available version 4 is really reliable.
I have the impression that it’s displaying incorrect data.

Has anyone else noticed reception problems with such a poor RSSI at short range?

Sincerely,
Eric.

2

Thanks for reaching out! To help us troubleshoot this more accurately, could you please clarify which hardware version of the V4 you are using? Also, it would be helpful to know which firmware version is currently flashed onto the device.

3

Hi,
I don’t use Meshtastic, but my own sketch.
I ran another test. The transmitter is a V4.2.

Results:

  • V3.2 -26dBm (-26 !!! Seems to be not possible).

  • V4.2 -62dBm

Same power supply, same antenna, same code (except for the pin numbers).

See the photo. The V4 is on the left, the V3 on the right.

The black box you can just make out below is the transmitter. It’s located less than 20 cm from both receivers.

-26dBm, I agree with you, that seems impossible. And yet…

Could the problem be with the “RadioLib” library?

Regards,
Eric.

20260505_075832
20260505_0758321920×864 246 KB

4

Hi,
I don’t use Meshtastic, but my own sketch.
I ran another test. The transmitter is a V4.2.

Results:

  • V3.2 -26dBm (-26 !!! Seems to be not possible).

  • V4.2 -62dBm

Same power supply, same antenna, same code (except for the pin numbers).

See the photo. The V4 is on the left, the V3 on the right.

The black box you can just make out below is the transmitter. It’s located less than 20 cm from both receivers.

-26dBm, I agree with you, that seems impossible. And yet…

Could the problem be with the “RadioLib” library?

Regards,
Eric.

My sketch if needed (testdbm.zip)

5

Hello Eric,

Thank you very much for sending your sketch and for the detailed explanation.

After checking the code, one important point stands out: the sketch is clearly written as an adaptation for Heltec V3.2. Because of this, the test result cannot be used as a direct and reliable performance comparison between V3.2 and V4.2 simply by changing the pin numbers.

In addition, your test is being carried out at very short distance and with high transmit power. In such a close-range setup, RSSI values can become misleading and are not always suitable for judging the real reception performance of different hardware versions.

So based on the information currently available, we would not conclude that the Heltec V4.2 hardware is unreliable. At this stage, it appears more likely that the result is influenced by the V4 adaptation of the code and by the very short-range test conditions.

6

Hello,

Thank you very much for this feedback.

Indeed, I think it’s possible that, at such a short distance, the receiver is saturated and the measured RSSI value is incorrect.

I should have run some tests with a lower transmission power…

In the coming days, I will conduct further tests, making sure to maintain a distance of at least several meters between the transmitter and receiver.

Furthermore, I will validate an intermediate and identical power level on V3 and V4 (the two transmitters).

I will then check the received RSSI on the same receiver located several meters away. This will allow me to verify the values ​​more reliably.

I will get back to you if my measurements reveal anything interesting.

Sincerely,
Eric.

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