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!

The simple method to listen to QRSS signals
Very sensitive QRSS reception was already possible before the computer age! Indeed by ear, with the same sensitivity as with our computers! That is possible with a tape recorder with variable speed. As an example we take a QRSS signal with a frequency of 10140.050 kHz. The receiver is tuned 45 Hz lower at 10140.005 kHz. Then the QRSS signal at the audio output of the receiver, has a frequency of 45 Hz. We record this signal with the tape recorder with a very low speed of 2.4 cm/sec. And then we play this signal with a 16x higher speed of 38 cm/sec. All frequencies are 16x higher now. Our QRSS signal of 45 Hz is now audible with a tone height of 16x45 = 720 Hz! The QRSS band, 100 Hz wide, has become 1600 Hz wide now. The noise will be spread over a 16x wider frequency range, the signal to noise ration has been increased 16x! And the usual dot length of 3 seconds for a dot is 16x shorter or 0.18 seconds. The usual shift of 5 Hz has increased 16x and is now 80 Hz. The QRSS morse signal has become a normal audible morse signal of approximately 6 words per minute!


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.

Some reception results
Here some reception results. On the pictures, you can see the received signals. And below the picture is the link to an audio WAV file where the signals of the picture can be heard.


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.

Listen to OH3AVA

Not bad, even the weak part in the picture is still audible!!!
Another station:


GJ7RWT.
Here below the link to listen to the signal.

Listen to GJ7RWT

And at the same time, IQ2DP was audible:


IQ2DP. Even the very weak "i" is still audible!
Here below the link to listen to the signal.

Listen to IQ2DP

And 22 June 2012, G0BES was audible during an over coming thunderstorm:


G0BES during an over coming thunderstorm. Even weak parts of the signal are still audible!
Here below the link to listen to the signal.

Luister naar G0BES


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!

And SA6BSS at the bottom of the picture on 1490 Hz, very difficult visible and close to the strong signal of G0PKT, but audible!

And without 10 Hz audio filter, you do hear all signals at the same time, but on different tone heights.


REALISATION

The hardware
But I did not have a tape recorder anymore. And I did never have a Revox as you can see on the picture, they were well above my budget. And my receiver did not have an audio output of 45 Hz. The QRSS band in the 30 meter band is at the audio output of the receiver in the audio band of 1495 Hz - 1595 Hz. But we can simulate the tape recorder with a PC. We do make an audio recording of the receiver output. We can use this recording again and again. A QRSS signal in the audio band 1495 -1595 Hz is down mixed to 45 Hz and filtered with a 10 Hz wide audio filter. And then a WAV audio file is made that plays 16x faster than the original recording. Good to realize with the free software language Python.


The tape recorder is simulated with this program, written in Python.

The software-tape recorder
It works nicer than an old tape recorder and also does something extra than just recording and playing. A QRSS signal in the audio band of 1495 Hz - 1595 Hz is also down mixed to 45 Hz. And the low frequency band filter is also in the software. Frequenties and the bandwidth of the filters are variable.

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.

How to use
At the same time with the normal QRSS decoding software like ARGO or LOPORA, also this program runs in the RECORDwav mode on the same PC. When something special is visible on the ARGO pictures, I do decode with ARGO the WAV file that has been recorded at the same time. Then I do know the exact frequency of the desired signal. And then I do convert the desired signal with this program to make it audible.


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.

There are two solutions for the digital filters, a FIR filter and a IIR filter. a FIR filter is very stable but does need a shift register with very many taps. For a 10 Hz bandfilter even 600. And for every sample, all those 600 taps have to be multiplied with a certan factor and added. The multiplication factors do determine the shape of the filter. Very much calculations, 600 calculations per sample. But there is an exception, the so called Moving Average Filter. Here all multiplication factors of all the taps do have the value 1. Only the first and the last tap have to be added resp. substracted. And ony 2 calculations are required, regardless the length of the shift register or the number of taps. Such a filter is used here. Of course, the shape is not so good, there are many side bands. But here, three FIR filter are placed after each other, the 2nd with a bandwidth of 1.5x of the first and the third again with a bandwidth of 1.5x of the second filter. In that way, the first side bands of a FIR filter are suppressed by the zeroes of the subsequent FIR filter.

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.

But you can also use an IIR filter. The advantage of an IIR filter is that it needs a much shorter shift register, so much less taps. That is because a part of the output signal is fed to the input. But more than 4 poles seems to be not so good, then the filter does become too instable. Here you can switch two 4 pole filters after each other for a better slope of the filter. A better solution seems to be to place a number of 2 pole IIR filters after each other. But I do not have enough knowledge to do that.


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:

Required external modules (site-packages for the correct Python version!):
Download here the Python program by clicking the link here below:


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