The software I am writing for the experiments:-
Windows 95/98 Program called WinFrad:
Imports data acquisition files from the Protek 506 (RS232 interface) Digital Voltmeter and can then graph the data. Can apply a crude form of filtering (Hi-cut and Low-cut) and save as a binary file or in spreadsheet format.
Multiple sequential Protek 506 data files can be chained and saved in a binary format.
This program implements one of the several methods that I have been developing for the transmission of information using narrowband methods. The method implemented is Absolute Frequency Keying (AFK). The program transmits and receives characters by transmitting a tone for 47.6 seconds synchronised to the minute by the computer clock - the 12.4 seconds left over is used in receive mode to process the data acquired over the previous 47.6 seconds by performing a Fast Fourier Transform (FFT). The receive part of the program searches over the receive bandwidth for the largest signal and measures its frequency. It then translates that frequency into the encode character to receive the data. The bandwidth of the FFT is about 0.02Hz and so the channel spacing (the step change in frequency between the assigned frequency for each character) has been initially set to this value. Actually to be accurate the channel spacing is (1/47.554467) = 0.0210285Hz - where 47.554467 is the time for 512*1024 samples to be taken at a sampling frequency of 11025Hz. Also the starting frequency (for the space character) is 14.993334Hz to ensure that the FFT bins falls centrally over each tone.
E-mail me with comments, suggestions and corrections.
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