Open Source HF Digital Voice for Amateur Radio
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Open Source HF Digital Voice for Amateur Radio

No noise and up to 8 kHz of TX audio bandwidth from 1500Hz of RF.

RSGB 2018 Convention Lecture on FreeDV


FIR Bandpass Audio Filter

The picture below shows the spectrum of the RADE V1 signal, similar to other OFDM waveforms with a RF bandwidth of 1500Hz. The low and high band frequency edges are around -12dB from the peak. The bandwidth is effectively set by the SSB radio TX filter, but you can use the FIR Bandpass Audio Filter for more precise audio shaping.

RADE V1 Signal Spectrum

A ZIP file for self-execution of the Python filter software (shared by Matthew G6WPJ) has been created with minor changes. Save it to a directory and create a desktop shortcut. Enter the setup data as illustrated below:

FIR Bandpass Audio Filter Setup

This filter helps ensure cleaner digital voice audio when using RADE V1.

G4URH RADE V1 digital signal on 60 mtrs with thanks from Jeff (GW3UZS)

RADE V1 Signal Example

Understanding RADE V1 & OFDM

OFDM splits data into multiple slower streams transmitted on different subcarriers. Subcarriers are orthogonal, allowing efficient spectrum use and reducing interference.

PAPR (Peak to Average Power Ratio)

PAPR measures the maximum to average power in a waveform. In OFDM systems, signals can have large fluctuations, therefore, amplifiers must operate with headroom to avoid clipping.

Fast Fourier Transform (FFT)

FFT converts a signal into its spectral components and provides frequency information.

Phase Shift

Phase shift can mathematically affect the decode of RADE V1.

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