Heltec V4 TX power testing

Hardware
1

Hi,

This may be interesting for those running Heltec V4’s.

Also be aware that firmware v 1.13.0 fixes some issues on the Heltec V4 with regards to the “deaf” Rx issues but apparently also introduced a bug with regards to low power management.

Did a full sweep of the Heltec V4’s actual conducted TX output power using a spectrum analyzer. Turns out the GC1109 PA tops out around +27-28 dBm - settings above TX=18-20 give you zero extra power, just extra battery drain.
Quick summary:

TX=5 → +12.2 dBm (17 mW) - close to EU 868 MHz legal limit
TX=10 → +20.3 dBm (107 mW) - already over 25 mW ERP with any antenna
TX=20 → +27.7 dBm (593 mW) - hardware maximum
TX=22 and TX=24 → same as TX=18, PA is saturated

If you’re running solar/battery repeaters, this matters a lot - TX=5 vs TX=20 is a 35x power difference for the radio.
Full methodology and data table: Heltec V4: Measured TX Power Output Table (firmware setting vs actual conducted dBm) · Issue #1708 · meshcore-dev/MeshCore · GitHub
Also cross-posted to Meshtastic #8070 since it’s the same hardware.

Serge

2 Likes
2

Hi Serge, I got my V4 last week and I saw that it was pre configured to TX=10. So I increased it to maximum (TX=22) and I noticed that my device then switched itself off while sending. Also with TX=20 I sometimes got the same behaviour. So I lowered TX=18 which is running stable since a week. Still running v1.12.0 on it with android app 1.39.0. Short SMA antenna attached, powered by 2m USB cable. Best Tobias

3

Hi,

I personally dont use V4’s in repeaters and mainly for some testing here at home but I thinks its important information especially for those thinking about use it as a repeater. Glad you have it working!

Regards,

Serge