Slow Morse (Part 1)

AB INITIO, (Very Slow Morse)
It has been suggested that complete beginners, i.e. those aspiring to join the community of Radio Amateurs, but who have not yet attained a licence, would benefit from an explanation of some of the terms used in amateur radio. In a recent contribution to the newsletter, (special broadcast from German weather station DDH47), the terms QRSS and Bandwidth were used, and it is proposed to start by explaining the first of these. Related aspects will be discussed in later articles.

Morse Code was the earliest means of radio communication, long before broadcasting with speech and music became technically possible. Messages could be sent to and received from ships at sea and across the Atlantic, and were often in the form of telegrams. Morse is still used to-day by radio amateurs keen to contact very distant stations or under difficult reception conditions, due for example to magnetic storms and high noise levels.

In the very earliest days of radio, a number of “abbreviation codes” were developed to simplify and speed up transmission and reception, of which the best known are the “Q Codes”, and these were agreed internationally in the early 1900s. (There were well over 60 listed in the 1926 Radio Amateur’s Handbook). You may be familiar with some of them, such as QSO, (a conversation between two or more stations), QRP, (low power), QTH, (your location), QRM, (interference), QRN (atmospherics), etc. If the Morse Q Code is followed by a question mark, it is asking a question. For example, QTH? means “What is your location”, and the reply might be “QTH St. Albans”. A particular Q Code, (which I have to use sometimes because my Morse speed is not very fast), is QRS, which means “Send slower”. It is frequently followed by a number indicating “words per minute”, as a request to the sending station. For example QRS12 means “Please send at only 12 words per minute”.

In spite of Morse Code being an ancient technology, a recent variant of it has come into use employing a computer connected to the radio. In this, instead of listening to the signal, the signal is displayed as dots and dashes on a computer screen. (In fact, in the earliest days of Morse use, it also was not listened to but caused an “Inker” to mark a moving paper tape from which it was read). Because the “human eye-brain combination” is extremely good at picking out lines from a jumble of random dots due to background noise, (which will be explained later), the dots and dashes of the Morse Code can be read from a screen even if the signal is so weak that it is not audible from an ordinary radio receiver. The longer the dot or dash is displayed on the screen, the easier it is to decide whether or not it is a true signal or just a succession of random noise dots. So, the slower each letter is sent, and therefore the longer each dot or dash appears on the screen, the easier it is to pick it out from the background noise. Under extremely weak signal conditions, this is taken to extremes , with very long dots and dashes being sent and displayed on the screen. Such extremely slow transmissions are very difficult to decode by ear, (you tend to forget what the previous symbol was unless you write it down), and similarly difficult to send accurately by hand. So the message is usually sent from a computer keyboard with a program which forms the dots and dashes automatically. This powerful weak signal mode of extremely slow Morse Code has become known as QRSS, and when followed by a number indicates the length of a dot. Hence, QRSS3 means extremely slow Morse Code with a dot length of 3 seconds, (and a corresponding dash length of 9 seconds). Even slower modes such as QRSS30 or even QRSS120 exist and are used. All the normal spacings of the normal Morse Code in terms of dot length are preserved. These are hardly modes for long conversations but they do enable contacts to be made at long range under extremely difficult conditions. There are many other “keyboard to screen modes” with similar advantages under very poor reception conditions or very low transmitter power, but these are beyond the scope of an introductory article.

In a future article we will look at the nature of interfering noise, why it makes communication difficult, and how noise depends on the bandwidth of the receiver.

             John,   G0NVZ   in error


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