twotonedecoder

Decodes the frequencies of two-tone codes used in fire dispatch pager systems.. Calculates and displays the frequencies of the tones.

Cross-platform, free and open-source alternative to commercial software such as ComTekk Two-tone Decoder.

See also: Wikipedia article on Two-tone sequential calling.

How to run on Ubuntu:

Requires PyQt4, Numpy, and PyAudio.

On Ubuntu:

sudo apt-get install python-numpy python-qt4 python-pyaudio

To run:

python twotonedecoder.py

Screenshot

How it works

It uses a Schmitt Trigger to calculate each frequency.

It has a number of settings (shown with defaults):

• NUM_TONES = 2

  • Number of tones to measure sequentially before considering as a new tone group

• MIN_TONE_FREQUENCY_DIFFERENCE = 5.0

  • Minimum difference between two tone frequencies in Hz to consider them as different tones

• MIN_TONE_LENGTH = 0.200

  • Minimum length of time in seconds to consider a signal as a tone

• MAX_TONE_FREQ_STD_DEVIATION = 10.0

  • Maximum standard deviation in tone frequency to consider a signal as one tone

• SQUELCH = -70.

  • Loudness in dB, below which to ignore signals