Simple FM transmitter using gnuradio

Simple FM transmitter using gnuradio.

Tools needed:

• gnuradio 3.2
• grc (gnuradio companion)
• mpg123
• USRP

Mono FM transmission is very simple as all necessary blocks already exist in gnuradio. In this example we will show how to make a FM transmission from an mp3 stream for an Internet radio.

GRC Schema

Input file is a unix FIFO file that means that we need to feed it externally from the shell using these commands

Creation of the FIFO file (once):

mkfifo stream_32k.fifo

Decoding of an mp3 Internet radio station stream, conversion and output of raw linear samples to the FIFO:

mpg123 -r32000 -m -s  http://maxxima.mine.nu:8000 >stream_32k.fifo

Option "-m" is to convert stream to mono, "-r32000" perform sample rate conversion to 32kHz.