Computer
Always-on Ubuntu or Raspberry Pi OS system with USB, network, and audio output.
Core components
Weather
Davis sensors and WeatherLink Live are the current reference source.
Receiver
HackRF or Airspy plus a VHF airband receive antenna and appropriate feed line.
Transmitter
A legally operated aviation radio with a documented external mic/PTT connector.
PTT relay
USB dry-contact relay supported by the configured serial command protocol.
Audio interface
Radio-compatible cable with the isolation and level control required by the radio.
How everything connects
The relay is a switch, not a voltage source
Typical dry-contact arrangement: radio ground to COM and radio PTT to NO. The contact stays open at rest and closes only during transmission. Never feed the USB relay supply voltage into the radio PTT or microphone pins.
Use a continuity meter with radio and computer disconnected. Verify COM–NO is open at rest, closes only when commanded, and returns open after power is removed. Match every connection to the manual for the exact radio and accessory cable.
RF and audio installation
- Protect the receiver from transmitter overload and provide appropriate antenna separation/filtering for the site.
- Use outdoor-rated feed line, grounding, bonding, and lightning protection appropriate to the installation.
- Begin microphone audio at a low level. A strong but distorted transmission is usually overdriven, not underpowered.
- Test into a dummy load or controlled arrangement before connecting the deployed antenna.
- Keep receive and transmit checks separate until both are repeatable.
What changed from the original site
The earliest builds used Arduino or analog circuitry to detect clicks. Those diagrams remain useful project history, but the recommended build now performs detection in the SDR and uses the USB relay only for PTT. The WeatherLink discovery library is optional rather than required.