Using Naze32 with 432MHz UHF (or 433MHz Telemetry) - Harmonic RFI Caution

[Hands0n]

I saw the below issued from a regular on the Facebook "The Mini Quad Club" user group.  Although aimed at American users of UHF it may be significant to UK users also if using the 434MHz frequency for that purpose.

However, I note that in his commentary he mentioned 432MHz which of course is just about where UK-legal 433MHz Telemetry resides.  So, in this case, it may cause FC problems for UK users that have 433MHz Telemetry mounted to their aircraft with a Naze32 or one of its derivatives using the same SoC. 

As the author says, there is a potential for harmonic RFI to cause problems to the Naze32.

Something to be aware of if you experience strange or unpredictable Naze32 behaviour when using UHF or UK-legal Telemetry radios on board.

Pro-tip for those flying with UHF using a Naze32. This was a feature merged into baseflight a while back (before cleanflight really existed) and I kinda forgot about it.

CLI set command "emf_avoidance" defaults to 0. This keeps the CPU running at 72MHz. However, the 6th harmonic of 72MHz is 432MHz. Bad!

Setting "emf_avoidance" to 1 overclocks the CPU to 84MHz resulting in a 6th harmonic of 504MHz, or far away from your UHF control frequencies.

Should you want to check to see if it really worked, enable emf_avoidance then save and reboot your board. Once re-connected, go to the CLI and type "status".

You should see something like this:
# status
System Uptime: 1361 seconds, Voltage: 0 * 0.1V (3S battery)
CPU 84MHz, detected sensors: GYRO ACC ACCHW: MPU6050.n
Cycle Time: 1501, I2C Errors: 0, config size: 1928
Most importantly, ensure that you see "CPU 84MHz".
I should say that I';m not sure how this is implemented on anything other than the standard STM32F1 boards (Naze32) and it';s clones.

[Chippercheese]

I';ve had issues with 459mhz UHF w/ telemetry enabled. Everything is fine with telemetry turned off.

[teslahed]

I have also had issues with openLRSng with radio telemetry turned on (but not off). That';s because with it turned on your receiver is also transmitting and so much more likely to interfere with your flight controller. Even with radio telemetry turned off i have heard that you should enable the emf_avoidance = 1 option, just to make sure.