SondeMonitor is a specialized Windows software created by COAA that allows hobbyists to decode real-time telemetry from weather balloon radiosondes. By pulling raw audio from a radio receiver, it plots atmospheric metrics (temperature, pressure, humidity) and live GPS flight tracks.
Setting up SondeMonitor involves gathering the required hardware, establishing an internal audio bridge, and properly tuning the software. Phase 1: Gather Hardware and Software Requirements
Before diving into configuration, ensure you have the necessary tracking components:
Radio Receiver: An inexpensive RTL-SDR (Software Defined Radio) USB dongle is highly recommended.
Antenna: A quarter-wave ground plane antenna tuned to the 400–406 MHz UHF band where weather balloons transmit.
SDR Software: Applications like SDR# (SDRSharp) or HDSDR to process raw radio waves.
Audio Pipe: A software utility like VB-Audio Virtual Cable to route the audio from your SDR program directly into SondeMonitor.
Decoding App: The SondeMonitor installation file from the official COAA site. Phase 2: Route the Audio Stream
SondeMonitor relies entirely on pristine audio to decode data frames. Standard physical speakers will not work; you must bridge the programs digitally.
Download and install VB-Audio Virtual Cable. This creates a phantom audio output named CABLE-Input and a matching input named CABLE-Output. Open your SDR program (e.g., SDR#).
Navigate to the audio output settings and change the device from your speakers to CABLE-Input.
Crucial Step: Disable any native high-pass/low-pass audio filters. In SDR#, uncheck Filter Audio. Radiosondes use low-frequency baseband modulation; leaving audio filters on will destroy the telemetry data payload. Phase 3: Tune and Capture the Signal
To feed data into the system, you must lock onto a live radiosonde transmission.
Visit tracking hubs like SondeHub or the NWS Flight Predictor to identify the exact time and frequency of balloon launches in your area. Launches typically happen twice daily at 1200 UTC and 0000 UTC.
Tune your SDR software to the target frequency (usually between 400.000 MHz and 406.000 MHz).
Set the demodulation mode to NFM (Narrowband FM) or WFM (Wideband FM) depending on the balloon model.
Adjust the volume slider in your SDR panel until you see a clear, consistent audio signal waveform without clipping the volume into the red zone. Phase 4: Configure SondeMonitor
With the audio stream active, open SondeMonitor to link the receiver data. [email protected] | RS41 NG