I've got a circuit that has been plagued by RFI issues for years and I am going through the fifth version of my PCB design and I want to eliminate RFI issues once and for all.
The circuit and PCB is used for transmitting rocket telemetry and GPS data on amateur rockets that travel 10K feet to 150K feet high. I've got a PCB that is currently using a Teensy 4.1 MCU (Arm7), a UBLOX GPS, multiple I2C sensors (barometer, gyro, accelerometer), and it has over a dozen wires that connect to the board used to fire pyro separation, control cameras, sense events, etc. I also have a 1 watt LoRa radio in the 430 Mhz range transmitting using a 1/4 wave dipole antenna. Unfortunately, the radio and antenna need to be within inches of the PCB, as there is no practice place to relocate the antenna or radio. In the smallest footprint, the PCB and radio "avionics bay" are self-contained in a 3" round by 14" long tube.
My issue is that the one watt UHF packet transmissions often interfere with the 400hz I2C bus or the Teensy SPI bus used for flash memory logging. In my last round of design I isolated power for the radio and MCU, I used a star topology for my ground/returns, ferrite beads on all the IO lines, y-caps on power, and a third filled-in layer on the PCB tied to ground.
For my next version, I plan to put a complete RFI shield around the top and the bottom of the PCB components using the WE ShielDIY with the SMT clips on both sides. I also plan on connecting all IO to the shield with 470pf caps, along with 50 ohm resistors in series on each IO line.
Having a relatively high power UHF transmission so close to the board is really unfortunate, but there is no way to design around it. Let me know if you have any other suggestions, especially for filtering out external 430 Mhz noise.
Thanks!
The circuit and PCB is used for transmitting rocket telemetry and GPS data on amateur rockets that travel 10K feet to 150K feet high. I've got a PCB that is currently using a Teensy 4.1 MCU (Arm7), a UBLOX GPS, multiple I2C sensors (barometer, gyro, accelerometer), and it has over a dozen wires that connect to the board used to fire pyro separation, control cameras, sense events, etc. I also have a 1 watt LoRa radio in the 430 Mhz range transmitting using a 1/4 wave dipole antenna. Unfortunately, the radio and antenna need to be within inches of the PCB, as there is no practice place to relocate the antenna or radio. In the smallest footprint, the PCB and radio "avionics bay" are self-contained in a 3" round by 14" long tube.
My issue is that the one watt UHF packet transmissions often interfere with the 400hz I2C bus or the Teensy SPI bus used for flash memory logging. In my last round of design I isolated power for the radio and MCU, I used a star topology for my ground/returns, ferrite beads on all the IO lines, y-caps on power, and a third filled-in layer on the PCB tied to ground.
For my next version, I plan to put a complete RFI shield around the top and the bottom of the PCB components using the WE ShielDIY with the SMT clips on both sides. I also plan on connecting all IO to the shield with 470pf caps, along with 50 ohm resistors in series on each IO line.
Having a relatively high power UHF transmission so close to the board is really unfortunate, but there is no way to design around it. Let me know if you have any other suggestions, especially for filtering out external 430 Mhz noise.
Thanks!