rtl_multi is a tool for streaming RTL-SDR samples over multicast, allowing multiple clients to receive the same SDR data without creating multiple device connections. It supports both server and client modes.

• Stream SDR samples from a single RTL-SDR device over multicast
• Multiple clients can subscribe to the same stream
• Lightweight and easy to configure
• Supports auto or manual tuner gain

• RTL-SDR compatible device
• Linux, macOS, or Windows environment
• Go-compiled rtl_multi binary

rtl_multi can run in server mode (broadcasting samples) or client mode (receiving samples).

In server mode, rtl_multi reads samples from an RTL-SDR device and broadcasts them over multicast.

Example command:

./rtl_multi -device 0 -freq 145.100 -gain 0 -samplerate 2.048 -mcast-addr 239.10.20.30:1234

Options:

• -device 0 : Use the first RTL-SDR device
• -freq 145.100 : Set the center frequency to 145.1 MHz
• -gain 0 : Automatic gain control
• -samplerate 2.048 : Sample rate in MHz
• -mcast-addr 239.10.20.30:1234 : Multicast address and port

In client mode, rtl_multi subscribes to a local TCP server that bridges the multicast stream for SDR applications.

Example command:

./rtl_multi -client -tcp-addr 127.0.0.1:1234

Options:

• -client : Enables client mode
• -tcp-addr 127.0.0.1:1234 : Address of the local TCP server receiving the multicast stream

1. Start the server:

./rtl_multi -device 0 -freq 145.100 -gain 0

2. Start one or more clients on the same network:

./rtl_multi -client

3. Connect SDR software (e.g., GQRX, SDR#) to the TCP server address 127.0.0.1:1234 to view the stream

• Multicast addresses must be within the IPv4 multicast range (224.0.0.0 to 239.255.255.255)
• Ensure network routers allow multicast traffic if streaming across subnets
• Multiple clients can receive the same SDR stream without additional load on the network