Fix GC1109 FEM LNA being used for Heltec v4 RX

[weebl2000]

I was experiencing very bad RX with my heltec v4 so I investigated and debugged.

Turns out everything handling the LNA/PA is completely fine, the only problem was the SX1262 boosted gain was enabled. If you disable this the RX is golden. 🥇

Actually, the problem was radiolib was trying to manage things.

Summary of Changes

1. HeltecV4Board.cpp - Enhanced RF Switch Control

Added detailed comments explaining the GC1109 FEM chip operation:

• PA_POWER (pin 7): Always HIGH to power the GC1109
• PA_EN (pin 2): Always HIGH (enables both RX and TX)
• PA_TX_EN (pin 46): The actual RF switch - LOW=RX/LNA, HIGH=TX/PA

2. platformio.ini

Added RF switch pin definitions at variants/heltec_v4/platformio.ini:34-35:
-D SX126X_RXEN=RADIOLIB_NC ; No separate RX enable pin
-D SX126X_TXEN=46 ; TX enable pin controls RF switch

How This Fix Works

The root cause was that RadioLib didn't know about the external GC1109 RF switch. Without the SX126X_RXEN/TXEN definitions, RadioLib never called setRfSwitchPins(), so it couldn't automatically manage PA_TX_EN during RX/TX transitions.

Now when you initialize the radio, CustomSX1262.h will automatically call:
radio.setRfSwitchPins(RADIOLIB_NC, 46); // RX=not used, TX=pin 46

This tells RadioLib to:

• Set pin 46 LOW when receiving (RX path through LNA)
• Set pin 46 HIGH when transmitting (TX path through PA)

[fschrempf]

According to @jbrazio here, it depends on the antenna whether RX boosted gain is benefitial or not. So if you disable it, it might help you but make things worse for others. If that's true, then we should leave this as is an go for the solution in #1164.

[weebl2000]

According to @jbrazio here, it depends on the antenna whether RX boosted gain is benefitial or not. So if you disable it, it might help you but make things worse for others. If that's true, then we should leave this as is an go for the solution in #1164.

Yeah maybe, I haven't tested with a lot of antennas yet. There's definitely something funky going on with the PA/LNA and the RX gain though.

[weebl2000]

According to @jbrazio here, it depends on the antenna whether RX boosted gain is benefitial or not. So if you disable it, it might help you but make things worse for others. If that's true, then we should leave this as is an go for the solution in #1164.

It'

According to @jbrazio here, it depends on the antenna whether RX boosted gain is benefitial or not. So if you disable it, it might help you but make things worse for others. If that's true, then we should leave this as is an go for the solution in #1164.

Yeah maybe, I haven't tested with a lot of antennas yet. There's definitely something funky going on with the PA/LNA and the RX gain though.

@fschrempf It gets more tricky. But I think we actually might just need to set SX126X_DIO2_AS_RF_SWITCH=false since we are handling the TX/RX mode on the PA/LNA. But I am getting variying results with improvements or not. I will try running tests for longer to really see a difference 👀

[weebl2000]

Updated with latest finding. I have tested for limited time but RX is heaps better, so others please do test!

[weebl2000]

I was asked to build the firmware, here you go for ble companion and repeater

• https://x230.weebl.me/public/heltec_v4_main+RX_fix_companion_radio_ble.bin
• https://x230.weebl.me/public/heltec_v4_main+RX_fix_repeater.bin

realized heltec wireless tracker v2 uses same chip:

• http://x230.weebl.me/public/heltec_tracker_v2_main+RX_fix_companion_radio_ble.bin
• http://x230.weebl.me/public/heltec_tracker_v2_main+RX_fix_repeater.bin

[dt267]

[perry99]

I was asked to build the firmware, here you go for ble companion and repeater

• https://x230.weebl.me/public/heltec_v4_main+RX_fix_companion_radio_ble.bin
• https://x230.weebl.me/public/heltec_v4_main+RX_fix_repeater.bin

The repeater is also a companion firmware:-(

[weebl2000]

Oops let me check

[weebl2000]

I was asked to build the firmware, here you go for ble companion and repeater

• https://x230.weebl.me/public/heltec_v4_main+RX_fix_companion_radio_ble.bin
• https://x230.weebl.me/public/heltec_v4_main+RX_fix_repeater.bin

The repeater is also a companion firmware:-(

Try now. Same URL.

sha256sum *bin
14f0617247fb9599d66e2f93796dbca628f82a0f0b4590b548eba18f10eac134  heltec_v4_main+RX_fix_companion_radio_ble.bin
41fa50ff5d1dd33bdd6367d6ebbcee2df464ac650717a27897caa195a7b103e3  heltec_v4_main+RX_fix_repeater.bin

[perry99]

I was asked to build the firmware, here you go for ble companion and repeater

• https://x230.weebl.me/public/heltec_v4_main+RX_fix_companion_radio_ble.bin
• https://x230.weebl.me/public/heltec_v4_main+RX_fix_repeater.bin

The repeater is also a companion firmware:-(

Try now. Same URL.

sha256sum *bin
14f0617247fb9599d66e2f93796dbca628f82a0f0b4590b548eba18f10eac134  heltec_v4_main+RX_fix_companion_radio_ble.bin
41fa50ff5d1dd33bdd6367d6ebbcee2df464ac650717a27897caa195a7b103e3  heltec_v4_main+RX_fix_repeater.bin

Thank you!