What is QRSS ?

Received QRSS image.

What is QRSS? (A definition/Explanation)

The Receiver, The Computer and F.F.T. Software.

Practical QRSS Operation.

The Challenge of QRSS.

Will QRSS teach me anything? 

Links to more information about QRSS.

What is QRSS (A Definition and Explanation of the term "QRSS")

The term "QRSS" is derived from the Q-Code "QRS" which is used in CW operation to ask an operator to "please send more slowly" or (when followed by an interrogative) "shall I send more slowly".

QRSS is an extension of QRS and intended to indicate "I will send very much more slowly". But why send more slowly? Well, in regular CW operation an operator may ask another operator to send more slowly when the propagation conditions are poor and the signals are just above the noise threshold. By sending more slowly the operator receiving the signal can often successfully decode the message which is probably only just above the noise floor. This is thanks to the human ear/brain combination which is able to separate the weak wanted signal from the unwanted background noise. In practice a point is reached when even the best and most experienced operator will not be able to copy the weakest signals which are close to the noise floor of the receiver or frequency channel.

A significant "boost" to the signal-to-noise ratio can be obtained by reducing the bandwidth of the receiver. This works because the wanted signal (Morse code in this example) is a narrow bandwidth mode and by making the receiver bandwidth only slightly wider than the wanted signal a significant amount of the noise in the communication channel can be removed. The four images below help to illustrate this concept more clearly. The upper two images show a Morse signal which is being received using a bandwidth which is considerably wider than that which is required for the mode. The net result is a poor signal-to-noise ratio. The lower two images show the same CW signal with the same signal strength as in the previous examples but now the receiver bandwidth has been reduced such that it is just a little wider than the wanted CW signal. The reduced bandwidth has little or no effect on the wanted signal so the overall wanted signal strength is the same as in the previous examples. However, the reduced bandwidth has changed the situation with the unwanted noise. While the amplitude of the noise is the same as in the previous examples the reduced bandwidth has now reduced the amount of noise which can pass through the channel. Since the wanted signal is largely unaffected and the noise has been reduced the CW operator now enjoys a much better signal-to-noise ratio and is able to copy the Morse signal much better.

Poor S/N image 1

  Poor S/N image 2

Good S/N image 1  

Good S/N image 2

The images above were created with the aid of the excellent M0KGK SDR software.

The above explanation and images demonstrate what all good CW operators and short wave listeners already know but let us now take the examples above a stage further. Lets say for the sake of example our very experienced CW operator/SW listener is trying to copy (or just detect the presence of) an even weaker signal. The signal is so weak that even with the narrowest possible bandwidth setting for the mode the signal is only barely discernible against the background noise. So what does he/she do now?

The Receiver, The Computer and F.F.T. Software.

Continuing the discussion above... If you take the audio signal from the receiver which consists mostly of noise components plus a very weak wanted signal component (near to or just below the noise floor of the system) and then perform a mathematical process on the audio signal called a "Fast Fourier Transform" (or F.F.T.) it then becomes possible to detect very weak signals. This is achieved by feeding the audio signals from our receiver into a sound card of a P.C. which is running F.F.T. software. Using the F.F.T. software it is then possible to detect very weak signals against a background of noise. The process is so effective that signals which are inaudible and undetectable by the human operator can be rendered fully detectable by the P.C./software combination.

The software is able to achieve this by breaking the audio signal spectrum down into a series of very narrow bandwidth channels and examining each channel very closely for signs of a "coherent" signal. The noise signal generally has a random frequency distribution across the spectrum of frequencies examined, by looking at the the spectrum of frequencies over a period of time it will be found that the random nature and frequency distribution of the noise results in low correlation over time and can be ignored. A wanted signal (even though it is weak) will tend to occupy the same frequency over a period of time and result in a much higher correlation which makes it "stand out" from the background noise. By continually averaging the results of an F.F.T. and repeating this process over a period of time a weak wanted signal can be readily detected against a background of noise. This effectively gives the operator a massive improvement in the signal-to-noise ratio of his/her receiving system with the ability to consistently copy/decode weak inaudible signals.

There is however a penalty for this much improved weak signal detection ability. First of all it is a s-l-o-w process, in fact the weaker the wanted signal is the slower the process must become in order to render the signal detectable. To receive single elements of a QRSS Morse signal may take several tens of seconds. Secondly, in order for the F.F.T. software to successfully detect the weak signal against the noise background the wanted signal must be as coherent as possible. In other words, there is a strong requirement for both the transmitter and the receiver to posses a very high degree of frequency stability.

Practical QRSS operation.

By now it will be clear that looking for s-l-o-w sub audible signals against a background of noise requires considerable patience. QRSS operation is definitely not another real time keyboard-to-keyboard digital mode. While computers are involved in the sending/receiving of QRSS the operator is not required to sit at the terminal for long periods. In QRSS operation it is customary to set the system running (in TX or RX) and check on it from time-to-time.

Receiving QRSS.
Receiving QRSS requires two items of hardware and some suitable software. The items of hardware are a suitable receiver for QRSS and a P.C. equipped with a sound card. The P.C. will also need suitable software for receiving and displaying QRSS signals. Three examples of QRSS signals received using different software packages are shown below.

Argo example.   Spectran example.  Spectrum Lab example.

The three images above show some examples of QRSS signals as they appear on the screen of a PC running suitable audio spectrum analyzer software. In the first example (above left) Argo has been used to display the QRSS signals, in the second example (above center) Spectran has been used and in the third example (above right) Spectrum Lab has been used. Argo (by I2PHD) is perhaps the easiest to use and recommended for those who are new to QRSS, Spectran (also by I2PHD) is slightly more complex but offers additional features not found in Argo. Spectran is very versatile and can be used for other modes and applications. Spectrum Lab (By DL4YHF) is a very professional package and can also be used to generate tones and complex signals making it suitable for QRSS TX applications. This would be the package of choice for those wanting to generate the more "exotic" QRSS modes.

In each of the examples above the software performs the FFT described earlier and presents the user with a display of  frequency (vertical axis) with respect to time (horizontal axis), the display scrolls horizontally so that the results can be observed over an extended period of time. Typically, the display will be set-up to show just over 100 Hz of the received audio bandwidth containing the QRSS signals. This 100 Hz window is user definable in all cases. In the case of a CW carrier you might expect to see a straight white line running horizontally across the screen, if the signal is frequency shift keyed (FSK) then you may expect to see FSK encoded Morse characters or patterns similar to the examples shown above. Receiving equipment for QRSS must have exceptionally good frequency stability to be effective. A more in-depth discussion about the hardware/software requirements for successfully receiving QRSS and links to suitable QRSS receiving equipment projects can be found here. Receiving QRSS

Transmitting QRSS.
Most QRSS operators construct a simple low power home-brew transmitter which incorporates the signal frequency components of the transmitter and some form of simple automated keying arrangement to send simple messages and/or patterns using F.S.K. (Frequency Shift Keying) with a computer only being required for more complex modes such as multi tone "Hell". Transmitting equipment for QRSS must also have exceptionally good frequency stability to be effective. More information and links to QRSS transmitting equipment can be found here. Transmitting QRSS

The Challenge of QRSS.

So where is the challenge of operating QRSS? Well, several challenges exist and this brief text just outlines a few of them. First of all, while it is possible to use "black box" manufactured equipment for QRSS operation a great deal of satisfaction and experience can be gained from building ones own custom made equipment. Because of the low power levels used in QRSS operation (typically 500 mW or less) construction of a complete transmitter becomes greatly simplified. QRSS transmitters share roughly the same level of complexity as a small QRP transmitter. Receivers for QRSS can be just as simple yet provide exceptionally good performance. Because of the simple nature of both QRSS transmitters and receivers coupled with the unique requirements for QRSS equipment the use of home construction techniques becomes completely viable and cost effective. More information on the receiving and transmitting of QRSS can be found here...

Receiving QRSS
Transmitting QRSS

One of the single most important features of both transmitters and receivers for QRSS operation is frequency stability, this can be a major challenge in its own right. Most (though by no means all) of the QRSS operation takes place in the 30 Mtr amateur band in the sub-band between 10.140000 MHz and 10.140100 MHz (100 Hz window) with the typical QRSS signal using a bandwidth of less than 5 Hz. This is a pretty tight window so both good frequency calibration and high frequency stability are required.

Consider this, there are 1000 mm to every Metre, 1000 Metre to every Kilometer, now imagine a straight road just over 10 km long (some 10, 000 000 mm long) and someone asks you to walk some distance along that road and accurately mark off a 100 mm section of that road. You are then asked to accurately mark off a 5 mm section within the 100 mm section! This is a rough comparison of the sort of accuracy required for successful QRSS operation. So, for successful QRSS operation in the 30 Mtr band an accuracy of better than 1 part per million is required. Is that challenging enough for you?

In reality achieving this level of accuracy and stability is not as difficult as it might first appear. Several standard frequency transmissions exist which can be used for frequency calibration. Maintaining the high level of frequency stability required can readily be achieved with an Oven Controlled Crystal Oscillator or O.C.X.O. More information on home-brew frequency calibration and temperature controlled crystal ovens can be found on this web site here...

An MSF Locked Frequency Standard for QRSS Calibration.
Crystal Ovens for QRSS Applications.


Will QRSS teach me anything?

Aside from the possible challenges of  the design, construction, calibration and operation of home-brew QRSS equipment there are other aspects of QRSS operation which may offer even greater challenges.

Because of the slow nature of QRSS operation we transmit or monitor on the same frequencies for extended periods of time. During these extended periods the propagation conditions often change quite significantly. By observing the received QRSS signals over long periods it it possible to observe propagation phenomenon such as multi path reception, Doppler shifted multi path signals, short skip signals, long path propagation and other phenomenon.

One of the big surprises for me was just how often propagation conditions existed which permitted low power signals (500 mW or less) from modest antennas to be received half way around the world. Another surprise living here in the UK was to find that short-skip on 30 Mtrs was a much more common event than I had first thought with signals sometimes less than 150 km away being received at very high signal strengths for long periods.

Links to more information about QRSS

I hope this brief explanation of QRSS has been helpful in defining QRSS for you, if I have failed to clarify the meaning of "QRSS" then try the links at the bottom of this page starting with the excellent on-line presentation by Don L. Jackson (AE5K) which takes the reader through QRSS step-by-step and explains in pictures and words how the mode works. The presentation can be viewed on-line in web page (HTML) format or downloaded as a Powerpoint97 file (about 8 M/Bytes) to run off-line on your PC.

If you would like to know more about the technical side and modes used in QRSS then take a look at the second link below (Rik Strobbe, ON7YD, "Extreme narrow bandwidth techniques"), this provides a very well presented in-depth technical discussion about QRSS modes. Also have a look at  "QRSS and you", (third link down) this is another page offering a similar explanation of QRSS to my own but from a different perspective. Finally, the last link takes you to the links page on this web site where you will find many QRSS resources including hyper links to the web pages of other QRSS enthusiasts.

Excellent on-line QRSS presentation by Don L. Jackson, AE5K. Can also be downloaded as a PowerPoint97 presentation

Rik Strobbe, ON7YD, "Extreme narrow bandwidth techniques"  

QRSS and you.

Other links to QRSS information and resources.

Well, that’s about it, thank you for reading this and please send any questions, comments or "heckles" etc to the e-mail address linked below.

e-mail QSL


Des (M0AYF)