How does VTX Power dynamically control the Video Transmitter?

I wired up an EACHINE TX805S 5.8GHz AC VTX to my Kakute H7 V2 as shown below.

Everything is working as expected but what I still cannot understand, and I don’t even know if its working is the VTX functionality of Copter 4.3. Here’s my parameter settings:

In the Messages TAB of Mission Planner, series of messages regarding the VTX Frequency and transmission power is spamming the message TAB. In the screen show below, the power is 0mW but I can still see video in the googles. I was expecting that there will be no video sent out at 0mW power output.

In my radio, I assigned an output to control RC10 and when I set it to MIN, the power displayed in the message TAB is 0mW while if I set it to MAX the power displayed in the message TAB is 1000 mW.

But looking at the wiring diagram, the Power Supply input of TX805S which is 7-24V is connected to the VTX output of the flight controller.

How can the flight controller dynamically control the power output of the video transmitter? Does it output a proportional voltage at the VTX output depending on the setting of the potentiometer in the radio?


Does it have a recognized protocol?

For future reference you can often just do a Google search for the Wiki. In this case “ardupilot vtx”

You need to wire the smart audio pin to a UART TX pin

Hi @ Andy,

Does the Smart Audio control the VTX Power? I don’t have an extra UART but if the Smart Audio is the one controlling the VTX Power, I may need to remove my Lidar connectred to one UART and use that UART for teh Smart Audio. What is the SERIALxPROTOCOL settings of the Smart Audio? Is it 37?


It’s all in the wiki - yes it controls VTX power

Can you use this " * if bit 3 is set, then the TX and RX pins are effectively swapped internally." to use a RX pin instead of a TX pin? I read that in the wiki and it sounds like it. My FC has a UART with only the RX exposed and NOT the TX pin but I would like to utilize it still if I can.

Only if its an F7 or H7. F4 does not support pin swap

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I never had success in setting up VTX and would like to give it another try. I’ve read the WIKI and would like to get some clarification on two settings specified in the screen shot below. Any help would be greatly appreciated.

Lastly, are my VTX parameter settings are correct? The intent is to be able to control the VTX power using potentiometer S2 in my TX16S radio and when the copter is on disarm state, the VTX power will switch to Pit mode.

I found this parameter settings in the XF Nano Div Rx. Can somebody confirm if I need to set Output 3 of the NANO Rx to Smart Audio and then directly connect the Smart Audio wire of the VTX to Output 3?

If this is the wiring connection, how will the flight controller know the power settings of the VTX so it can display it in the OSD? I think I am missing something else.