The current avionic modules still cause interference on my VHF air-band radio. Whenever the power switch for the avionics is turned on, the radio intermittently shows the Rx light and plays channel noise. Turning the squelch all the way up reduces the issue to some extent. Unplugging the antenna on the radio stops the issue, leaving me to believe that I am dealing with radiated emissions from the avionics, rather than conducted emissions through the power supply.

Below are some design notes for the next hardware revision to mitigate the EMC issues:

• run the micro-controller at 80 MHz rather than 120 MHz (move the I/O and transistor switching noise further away from the air-band VHF frequencies)
• PCB ground fill on both sides (traces become more like coplanar waveguides rather than radiating antenna elements)
• PCB solder pads for an EMC cage (brass sheet bent into a box)
• use in-line termination resistors for signals between integrated circuits on the same board
• use low noise switching power supply modules

The whip antenna position (in close proximity to the instrument pod) and limited ground plane (using the goose neck on the aluminium frame) are not ideal on my microlight trike. The aluminum frame structure and many stainless steel support wires make the antenna mounting challenging and distort the radiation pattern. I have not measured the VSWR, but expect quite a bad impedance match and significant reflections. If the next hardware revisions still cause interference issues, I will consider mounting a V or dipole antenna to the king post or the back of the keel.