Brian Haddad: Difference between revisions
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'''''Introduction''''' |
'''''Introduction''''' |
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:PSK31 was developed by Peter Martinez (G3PLX) in 1998. PSK31 varies in amplitude and phase, but not frequency. This is extremely useful in amateur radio. When there is constant phase, it is considered to be a 'one', when the phase shifts, it is a 'zero'. |
:PSK31 was developed by Peter Martinez (G3PLX) in 1998. PSK31 varies in amplitude and phase, but not frequency. This is extremely useful in amateur radio. PSK31 uses Varicode; a unique binary alphabet where no letter can be found in another. A transmission begins with several zeros so the decoder can synchronize to the exact frequency. The continuous zeros phase shift at a rate of 31.25 per second; hence the name. Each character begins with a 'one', and ends with double zeros ('00'). When there is constant phase, it is considered to be a 'one', when the phase shifts, it is a 'zero'. |
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:Our project involved creating a "transmitter" to simulate a real signal that our decoder could identify the frequency and interpret the message. The transmitter uses a look-up-table to convert ascii characters to Varicode, then modulate the carrier frequency and add noise. The receiver does the same thing in reverse. The transmitter sends two signals simultaneously. At the moment, both signals have the same message and phase, but are transmitted on separate carrier frequencies. Very little improvement is needed to improve the decoder so it can receive multiple messages and phases simultaneously. To simulate a real signal, the signal is written to a .wav file to be read by the decoder. This ends the transmitter portion. The decoder begins by reading the .wav file and sending it to a Fourier transform so we can locate the frequencies the signal is transmitting on. Once the frequencies are determined, the signal goes through a bandpass filter at one of the identified carrier frequencies to remove the noise associated with it. The next step is finds the peaks of the signal or local maxima, and interpolates them to create a wave. (Figure 1, plot 3) shows the signal at this stage. Next, find the local minima and mirror it over the t-axis from that point to the end of the transmission(Figure 1, plot 4). |
:Our project involved creating a "transmitter" to simulate a real signal that our decoder could identify the frequency and interpret the message. The transmitter uses a look-up-table to convert ascii characters to Varicode, then modulate the carrier frequency and add noise. The receiver does the same thing in reverse. The transmitter sends two signals simultaneously. At the moment, both signals have the same message and phase, but are transmitted on separate carrier frequencies. Very little improvement is needed to improve the decoder so it can receive multiple messages and phases simultaneously. To simulate a real signal, the signal is written to a .wav file to be read by the decoder. This ends the transmitter portion. The decoder begins by reading the .wav file and sending it to a Fourier transform so we can locate the frequencies the signal is transmitting on. Once the frequencies are determined, the signal goes through a bandpass filter at one of the identified carrier frequencies to remove the noise associated with it. The next step is finds the peaks of the signal or local maxima, and interpolates them to create a wave. (Figure 1, plot 3) shows the signal at this stage. Next, find the local minima and mirror it over the t-axis from that point to the end of the transmission(Figure 1, plot 4). |
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Revision as of 19:05, 12 December 2012
Contact Info:
Email: brian.haddad(AT)wallawalla(dot)edu
Articles Added:
PSK31 Demodulation (In Progress)
Fall, 2012
- Partner Denver Lodge
Abstract
- This project demodulates at least two PSK31 signals with limited phase shifting.The approach begins by filtering the signal to find the peaks and interpolated to connect the maximums.
Introduction
- PSK31 was developed by Peter Martinez (G3PLX) in 1998. PSK31 varies in amplitude and phase, but not frequency. This is extremely useful in amateur radio. PSK31 uses Varicode; a unique binary alphabet where no letter can be found in another. A transmission begins with several zeros so the decoder can synchronize to the exact frequency. The continuous zeros phase shift at a rate of 31.25 per second; hence the name. Each character begins with a 'one', and ends with double zeros ('00'). When there is constant phase, it is considered to be a 'one', when the phase shifts, it is a 'zero'.
- Our project involved creating a "transmitter" to simulate a real signal that our decoder could identify the frequency and interpret the message. The transmitter uses a look-up-table to convert ascii characters to Varicode, then modulate the carrier frequency and add noise. The receiver does the same thing in reverse. The transmitter sends two signals simultaneously. At the moment, both signals have the same message and phase, but are transmitted on separate carrier frequencies. Very little improvement is needed to improve the decoder so it can receive multiple messages and phases simultaneously. To simulate a real signal, the signal is written to a .wav file to be read by the decoder. This ends the transmitter portion. The decoder begins by reading the .wav file and sending it to a Fourier transform so we can locate the frequencies the signal is transmitting on. Once the frequencies are determined, the signal goes through a bandpass filter at one of the identified carrier frequencies to remove the noise associated with it. The next step is finds the peaks of the signal or local maxima, and interpolates them to create a wave. (Figure 1, plot 3) shows the signal at this stage. Next, find the local minima and mirror it over the t-axis from that point to the end of the transmission(Figure 1, plot 4).
Matlab Script
% This script demodulates the PSK31 signal
Matlab Plots
- These are the plots
Results
- The end.