afskmodem

A software-defined Audio Frequency-Shift Keying modem designed for analog FM radios. Uses the device’s default audio input and output.

Source code

Releases

Usage Examples

Sending a message:

from afskmodem import Transmitter
t = Transmitter(1200)
t.transmit("Hello World!")

# Argument can be either str or bytes

Receiving a message:

from afskmodem import Receiver
r = Receiver(1200)
recv_data = r.receive(100, True)
print(recv_data)

# Set the second argument to True to decode as a UTF-8 string

Constructing a Transmitter with a custom training sequence:

from afskmodem import Transmitter
t = Transmitter(1200, 1.5)

Constructing a Receiver with a higher sensitivity:

from afskmodem import Receiver
r = Receiver(1200, 14000, 11000)

Note: Although it is possible to change these parameters, the defaults usually perform the best. The input device’s volume should be adjusted before changing the sensitivity of Receiver.

Writing to a .wav file with Transmitter:

from afskmodem import Transmitter

t = Transmitter(1200)
t.save("Héellóo World!", "afsk.wav")

# First argument can be either str or bytes

Reading from a .wav file with Receiver:

from afskmodem import Receiver

r = Receiver(1200)
recv_data = r.load("afsk.wav", True)
assert recv_data == "Héellóo World!"

# Set the second argument to True to decode as a UTF-8 string

Note: Input files for Receiver.load() must be 48khz 16-bit mono. Transmitter.save() outputs files in this format.

Supported Baud Rates

afskmodem supports common baud rates like 300, 600, 1200, 2400, 4800, and 9600. It can use any baud rate as long as it is a factor of the sample rate (48000).

Classes

Receiver

Receiver is configured with a baud rate and optional audio settings, and provides functionality for receiving and decoding messages.

Constructor parameters

baud_rate: (required, int, 300-12000) Baud rate for this Receiver

amp_start_threshold: (optional, int, 0-32768) Amplitude to detect start of signal

amp_end_threshold: (optional, int, 0-32768) Amplitude to detect end of signal

Member Functions

receive(timeout: float, string: bool = False) -> bytes|str - Listens and decodes a message. Takes a timeout in seconds. Set string to True to decode the result as a UTF-8 string.

read(filename: str, string: bool = False) -> bytes|str - Listens and decodes a message, reading input from the specified .wav file. Input file must be 48khz 16-bit mono. Set string to True to decode the result as a UTF-8 string.

Transmitter

Transmitter is instantiated with a mode and optional audio settings, and provides functionality for encoding and sending messages.

Constructor Parameters

baud_rate: (required, int, 300-12000) Baud rate for this Transmitter

training_sequence_time: (optional, float) Length of the training sequence in seconds

Member Functions

transmit(data: str|bytes): Encodes and transmits a message. If given a string, will encode it as UTF-8 before transmitting.

write(data: str|bytes, filename: str): Encodes and transmits a message, saving the audio to a .wav file instead of playing it. If given a string, will encode it as UTF-8 before transmitting.

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