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.
Requires PyQt4, Numpy, and PyAudio.
On Ubuntu:
sudo apt-get install python-numpy python-qt4 python-pyaudio
To run:
python twotonedecoder.py
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