A METHOD TO LISTEN TO QRSS SIGNALS!
(2012)
KLIK HIER VOOR DE NEDERLANDSE VERSIE
The method to listen to QRSS signals is...
An old tape recorder with variable speed!
We can improve the system even more by adding an audio filter.
That filter is 10 Hz wide (40 Hz - 50 Hz), but because we play 16x faster, it becomes 160 Hz wide.
A clear signal to start with. OH3AVA. When you click on the link here below,
you can hear this signal. It is played 16x faster than the original signal.
GJ7RWT.
Here below the link to listen to the signal.
IQ2DP. Even the very weak "i" is still audible!
Here below the link to listen to the signal.
G0BES during an over coming thunderstorm. Even weak parts of the signal are still audible!
Here below the link to listen to the signal.
Many signals! And you can also hear interference of an electric fence. Normally, that is 1 pulse per second.
But you do hear 16 pulses per second, because we play the signal 16x faster!
Here below the links to listen to the signals.
Listen to G0PKT on 1500 Hz, a very strong signal!
And G0MBA on 1605 Hz, hear how Hell sounds!
And G1IVG on 1528 Hz, a difficult visible signal, but excellent audible!
And G4JVF on 1550 Hz, Also a difficult visible signal, but excellent audible!
REALISATION
The hardware
The tape recorder is simulated with this program, written in Python.
RECORDwav
Continuous recordings of 20 minutes are made. These recordings are stored as audio WAV files with the date and time as the file name. This goes on till you press the stop button.
CONVERTwav
The recorded WAV files can be converted to 16x faster playing WAV files.
Asked is which filter you want to use. For 1 QRSS signal, you do use filter number 1, the FIR filter and you do select a bandwidth of 10 Hz. But when you want to listen to the whole band, then select the better filter 2, and IIR filter with a bandwidth of 100 Hz.
If the FIR filter 1 is selected, the bandwidth will be asked. The value of 10 Hz is good for 1 signal, but you can also try other values. However, the IIR filters do have fixed bandwidths and they are only correct if the sample rate is set to 6000 samples per second.
Then the frequency of the QRSS signal that has to be converted is asked. Or when you want to convert the whole QRSS band, the central frequency of the QRSS band.
And then the frequency where to the QRSS signal has to be down mixed. Normally that is 45 Hz, so with a 16x faster playing speed, you will hear a tone of 720 Hz.
Then the new speed will be asked, 16x is the default value.
And finally, you can increase the volume of the converted WAV file. Always easy when you do receive weak signals.
RECORD & CONVERTwav
I never used this option. But perhaps that someone else can do something with it.
Continuous recordings of 20 minutes will be made. After every recording, a converted WAV file will be made. When you have chosen a reception bandwidth of 100 Hz (filter 2) and 70 Hz as the frequency where the signal has to be down mixed to, you can hear the whole band at once and hear how the activity is.
PLAYwav
And for completeness, a PLAYwav button has been added, but it is better to use the standard audio player of your PC.
Something about the software
The conversion of the QRSS signal in the audio band of 1500 Hz to 1600 Hz to approximately 45 Hz is done by means of a low frequent SSB receiver. It works in accordance with the Weaver method.
The Weaver SSB receiver does use the phase method to suppress 1 side band. The first oscillator F1 is tuned to
the signal in the audio band of 1500 Hz to 1600 Hz. The second oscillator is tuned to the new frequency of 45 Hz.
And this is how you make such a receiver in software! The first mixer, two IIR filters as low pass filter and the second mixer plus adder.
The pictures here below were made with a multi carrier WAV audio signal. It consists of many small signals, separated 10 Hz in frequency from each other. That is why you do not see a constant curve, but many small signals, separated 10 Hz from each other.
Although the original FIR filter does have many side bands, it was quite good useable.
But the side band suppression can be much better. The conversion takes some more time then.
Three FIR filter after each other, the 2nd with a bandwidth of 1.5x of the first one
and the third one with a bandwidth of 1.5x of the second. In that way, the first side
bands of a FIR filter are suppressed by the zeroes of the subsequent FIR filter.
An IIR Butterworth filter, but more than 4 poles is not possible. In fact you have to place
more 2 pole IIR filters after eacht other due to the extreme gains that are otherwise required.
Two 4 pole IIR Butterworth filter after each other, a very nice filter!
SOFTWARE
Before you are using this program, you have to install Python. That is very simple. But read first something about Python by clicking the following link:WHAT IS PYTHON AND HOW DO YOU INSTALL PYTHON
As the source code of Python is written in ASCII, it is very simple to modify the program to you own requirements. Think for example about the size of the screen, the colors etc.
Required Python version: