MEPTs & QRSS Knights

In the previous posts we were described issues related to slow Morse code transmission, bandwidth (BW), signal to noise ratio (SNR) and operating modes such us QRSS and its variants. Today we will make one small step forward and we will see how these modes are used inside amateur radio for experimentation and propagation research. In future postings and within 3rd party references for experimentation with slow code transmission, you must keep in mind that the term "QRSS" is used in general.

MEPTs

For ionospheric propagation experiments the most common practice is the usage of radio beacons. Radio beacons are unattended transmitters that repeat a callsign in Morse code (most of the times) and the listeners by identifying each beacon can know if the specific moment of reception there is a propagation opening between their location and the location-country of the beacon. In many countries the amateur radio license forbids the licensee to operate a beacon without first obtaining special permission and/or an extension to the license. In some countries the licensing conditions relating to beacon operation are confusing. With QRSS operating it is quite common for low power transmitters to work for extended periods of time therefore it was felt among QRSS experimenters that is important to clarify their position with respect to beacons.

Since the QRSS experiments are directed at achieving the detection of very weak radio signals at great distances and examining how the prevailing propagation conditions affect those signals it was decided that a new term should be found to describe any QRPp slow code transmitting equipment which best suited these activities. After several threads on mailing lists related to QRSS experimentation over many months, the term "MEPT" was arrived that stands for Manned Experimental Propagation Transmitter. The "Manned" part of the term MEPT is simply to make clear that these transmitters are supervised at all times. The "Experimental" means just that, an experimental transmitter while the "Propagation" part of the term attempts to make it clear that QRSS transmitters are a method of observing propagation effects on radio signals. Above all QRSS experimenters try to avoid the term "beacon" because this can be a "sensitive" issue.

QRSS Knights

QRSS Knights is a worldwide known group of QRSS enthusiasts, that are doing experiments mostly on 30m (10140.0 - 10140.1 KHz) & 40m (7000.8 - 7000.9 KHz) and sometimes on 80m (3500.8 - 3500.9 KHz). I am not sure when they started to exist as group but I learned about them back in 2002. All of the experiments are done on QRSS, FSKCW, DFCW and some other slow code transmission modes like HELL. The maximum working power is below 500mW. Most of the times the power is 100 to 200 mW and there are cases were the experimentation goes down to the microwatts region. The QRSS Knights group consists from radio amateurs that work MEPTs or QRSS Grabbers and they exchange information and reception reports through the knightsqrss mailing list or the knightsqrss clipboard. As you may already understood… I am one of the QRSS Knights.

References:
[1] M0AYF, The term "M.E.P.T." explained, http://www.qrss.thersgb.net/MEPT.html
[2] QRSS Knights, Mailing List, http://cnts.be/mailman/listinfo/knightsqrss_cnts.be
[3] QRSS Knights, Clipboard, http://www.on5ex.be

QRSS, FSKCW & DFCW modes

In the previous post we described how effective is the reduction of the Morse code speed on the SNR and how much we can reduce our transmitting power if we reduce our code speed. Most of you may think: "Why we need to lower the code speed to extreme numbers (like many seconds per dot) since we can use some Watts and communicate in normal speeds?" Even that this question can be answered on many different ways, there are some cases where the transmission on extremely low speeds is the only option. One of them is the case were we need to transmit on ELF, SLF, ULF, VLF or LF bands where wavelength ranges from 100000km to 1km. In any of these bands the wavelength is so long that is impossible to construct a normal transmission antenna with length at least one quarter of the wavelength. In all cases the transmitting antenna will be very short compared to the wavelength and because of that its impedance will be many KOhms compared to the 50 Ohms of the transmitter output. In these cases we need special antenna tuners with huge tunable coils (variometers) that will match the impedance of our antenna with the impedance of the transmitter. The final result is a lot of power consumption on the antenna tuner and only a small part of the transmission power is radiated on the air (Effective Radiated Power or ERP). A typical example in amateur radio is the band of 136 KHz (LF) were we need at least 600 Watts of transmission power in order to produce only 1 Watt ERP! As we go lower in frequencies the radiated power becomes much lower and finally the ERP is the factor that defines what will be our Morse code transmission speed. Aside from the case that very low speed is mandatory, there are cases were radio amateurs experiment on high frequencies with very low code speeds just for the fun in order to play with QRPpp power levels and break MPW world records. There are several techniques (modes) for slow Morse code transmission. The most widely used from radio amateurs are QRSS, FSKCW and DFCW.

QRSS

QRSS is extreme slow speed CW, the name is derived from the Q-code QRS (reduce your speed). To take advantage of the very narrow bandwidth of the transmitted signal an appropriate filter at the receiver end is needed. Making a "software filter" using FFT (Fast Fourier transform) has some advantages over the old-fashioned hardware filters. One of the main advantages, when using it for reception of slow CW signals, is that FFT does not give you one single filter but you get a series of filters with which you can monitor a complete spectrum at once. This means that you do not have to tune exactly into the signal, something that can be very delicate at sub-Herz bandwidths. Also it is possible to monitor more than one QRSS signals at the same time. Further the long duration of the dots and dashes is unfavorable for aural monitoring. A solution to the above problem is to show the outcome of the FFT on screen rather than making it audible. The result is a graphic where one axis represents time, the other axis represents frequency and the color represents the signal strength. If the vertical axis represents time we call it a "waterfall" display while it is called a "curtain" display if the horizontal axis represents time. All this may sound complicated but it is easy to understand when you see the following example:

The picture above shows the signal of G3XDV as it was received on 15/01/05 from RU6LA on 136KHz with QRSS10 (10 second dots) on a two-way QSO that covered a distance of 2823km.

FSKCW

FSKCW means Frequency Shift Keying CW and is a variant of QRSS that instead of activate/deactivate the carrier, the carrier is always activated as long as the transmission lasts. During pauses between dots, dashes or characters the frequency is shifted downwards. Whilst the upper trace shown on the screen contains the morse information the lower trace is drawn during signal pauses. The advantage of this mode is its redundancy. If, for instance, a dash is falling into pieces caused by QRM there's still a chance to determine subsequently by checking the lower trace if the signal really had contained that dash or rather several dots.

The picture above shows the signal of WA5DJJ as it was received on 27/03/09 from WA0UWH on 10140KHz with FSKCW10 (10 second dots), the covered distance was 2176km.

DFCW

DFCW means Dual Frequency CW and is a combination of QRSS and FSKCW. In the LF band of 136KHz where the most common used mode is QRSS3, a very basic QSO will take about 30 minutes. Changing QRN levels and/or propagation during this period can have a vast effect on a QSO. Therefore the DFCW mode was developed that enhances the average speed by a factor of 2.5 to 3. In DFCW the element duration is replaced by the element frequency. So dots and dashes no longer have a different length but they are transmitted on a different frequency. Due to this frequency shift there is no space needed between the dots/dashes and the character space can be reduced to the same dot length. To make it even easier to read, especially during a sequence of dots or dashes, a short space (typically 1/3 of a dot length) is added between the dots and dashes. This reduces the average speed a bit, but is improves the readability and also reduces the transmission duty cycle. At a speed of 3 seconds per dot the CQ message will take 5'30" in QRSS while it will take only 1'54" in DFCW. The speed advantage of DFCW over QRSS can be taken in 2 ways, either by reducing the duration of a QSO or by increasing the dot length and working at a narrower bandwidth. The last means that, for the same duration of a QSO, the dot length in DFCW can be 2.5 to 3 times longer and as a result of this get a 4 to 5dB better SNR.

The picture above shows the signal of CT1DRP as it was received on 14/04/04 from OH1TN on 136KHz with DFCW120 (120 second dots), the covered distance was 3364km.

Reception of QRSS, FSKCW & DFCW

In order to receive signals of these modes you need of course an antenna and an SSB receiver for the frequency of interest. The audio output of the receiver must be connected to the soundcard of a PC and with the help of specialized software like: Argo, Spectran, SpectrumLab, QRSS VD and many others, you will able to receive and decode signals via the embedded FFT procedures.

References:
[1] Wikipedia, Radio spectrum, http://en.wikipedia.org/wiki/Radio_spectrum
[2] ON7YD, Extreme narrow bandwidth techniques, http://www.qsl.net/on7yd/136narro.htm
[3] DL6JAN, CWKtiny Instruction manual, http://www.proehl-elektronik.de/cwk/manual/manual5_e.html

Morse code 101 in WPM, BW & SNR

Morse code is a method of transmitting textual information as a series of on-off tones, lights or clicks that can be directly understood by a skilled listener or observer without special equipment. The International Morse Code encodes the Roman alphabet, the Arabic numerals and a small set of punctuation and procedural signals as standardized sequences of short and long "dots" and "dashes", or "dits" and "dahs". Because many non-English natural languages use more than the 26 Roman letters, extensions to the Morse alphabet exist for those languages.

A related but different code was originally created for Samuel F. B. Morse's electric telegraph in the early 1840s. In the 1890s it began to be extensively used for early radio communication before it was possible to transmit voice. In the early part of the twentieth century, most high-speed international communication used Morse code on telegraph lines, undersea cables and radio circuits. International Morse code today is most popular among amateur radio operators, where it is used as the pattern to key a transmitter on and off in the radio communications mode commonly referred to as "continuous wave" or "CW". Other keying methods are available in radiotelegraphy, such as frequency shift keying.

Time structure

The basic element of Morse code is the dot and all other elements can be defined in terms of multiples of the dot length. The other elements are dash (= dot length x 3), pause between elements (= dot length), pause between characters (= dot length x 3) and pause between words (= dot length x 7). An example is the word PARIS that has length of 50 dot lengths:

Words Per Minute

The word PARIS (shown above) is used as standard of the typical word in English plain text. Morse code speed is specified in words per minute (WPM). This means that if we transmit the word PARIS (that has length 50 dot lengths) in 1 minute then the speed is 1 WPM. Also if we send PARIS (or any other word 50 dot lengths long) ten times in a minute then the code speed is 10 WPM. In case of 1 WPM the duration of a dot is 60 seconds / 50 dots per minute = 1.2 seconds per dot. Also in any other speed we can define the dot length as equal to 1.2 seconds divided by the speed in WPM. Based on the above we can use the following formulas:

Speed (WPM) = 1.2 / Dot length (Seconds)

or

Dot length (Seconds) = 1.2 / Speed (WPM)

Bandwidth

A CW signal of 12 WPM means 12x50 = 600 dot lengths per minute or 600/60 = 10 dot lengths per second. Since pause between elements (dots or dashes) is equal to dot length, if a continuous series of dots is given at 12WPM this results in a 10/2 = 5 Hz square wave. If an RF signal is keyed with this series of dots we will get a carrier with 2 sidebands at 5Hz, resulting in a 10Hz wide signal.

This result based on a fundamental principle of trigonometry, that says that modulating a sine wave with another sine wave (which is actually multiplying the two waveforms) yields 2 signals, one at the sum of the frequencies and the other at the difference of the frequencies. This assumption is based on the case where the keying is not "hard" (rapid on-off) but with additional RC circuits we shape the square keying waveform to look like sine and have gradual (and not rapid) turn on/off. In real world "hard" keying is never used because the modulation of a carrier with a square wave is a disaster. It is known that a square wave is composed of an infinite number of harmonics and probably at least the first 30 or so are significant, so using hard keying means modulating a high frequency carrier sine wave with a low frequency square wave and the result will be a very wide frequency spectrum with a lot of sidebands that are waste of energy and production of interference.

Above we saw that a 12 WPM baseband signal produces a 10Hz wide RF signal and this leads to a ratio of 12/10 = 0.833. Concluding, we can say that the minimum bandwidth that is required to receive a CW signal undistorted is:

BW (Hz) = 0.833 * Speed (WPM)

Signal to Noise Ratio

Signal-to-noise ratio (often abbreviated SNR or S/N) is a measure used in science and engineering to quantify how much a signal has been corrupted by noise. It is defined as the ratio of signal power to the noise power corrupting the signal. A ratio higher than 1:1 indicates more signal than noise. In less technical terms, signal-to-noise ratio compares the level of a desired signal to the level of background noise. The higher the ratio, the less obtrusive the background noise is. Signal-to-noise ratio is defined as the power ratio between a signal (meaningful information) and the background noise (unwanted signal):

SNR = P signal / P noise

where P is average power. Both signal and noise power must be measured at the same or equivalent points in a system, and within the same system bandwidth. Because many signals have a very wide dynamic range, SNRs are often expressed using the logarithmic decibel scale. In decibels, the SNR is defined as:

SNR (dB) = 10 x log10 (P signal / P noise)

It is very easy to understand that in a receiver that gets CW signals, higher SNRs lead to higher possibilities for correct detections and decodes of the Morse code messages. A typical radio link consists from the transmitter, transmission line, transmitting antenna, air path, receiving antenna, reception line and the receiver. In order to calculate the SNR we need a LOT of information that range from "known" values such as the transmitting power, losses in transmission and reception lines, gains of transmission and reception antennas, signal bandwidth to other more complex and maybe completely unknown values like noise figure of the receiver and loss of the air path that depends from distance (that the airwave crossed) which most of the times is completely unknown and especially in HF bands where the airwave gets reflected by the ionosphere and we don’t know the number of hops nor if it was traveled via the short or the long path between the two locations.

If we want to improve the SNR we can do it by change one or more of the factors that affect SNR. We may increase SNR by increase the transmit power or the receive/ transmit antenna gains or decrease transmission/reception line losses but all these require changes in the equipment that is not always possible. We can also increase SNR by decrease the bandwidth. Why? A wider bandwidth includes more noise, so reducing receiver’s bandwidth will always increase SNR. In the previous section we saw that the bandwidth occupied by a CW signal depends from the Morse code speed in WPM and if we decrease the code speed in WPM then the bandwidth decreases.

All these mean that we may not be able to calculate the SNR accurately or not calculate it at all BUT we can calculate the improvement of the SNR (dB) of a lower code speed (WPM) against a higher code speed (WPM). In a few words this means that if we have established a communication link with e.g. 12 WPM and 10W of transmitting power if we reduce the code speed to 4 WPM we will have an improvement on SNR several dBs BUT since the SNR of 12 WPM was enough for correct decoding of Morse code messages we can decrease the transmitting power of the 4 WPM transmission the same amount of dBs (as the improvement on SNR from 12 WPM to 4 WPM) and achieve on 4 WPM the same SNR with 12 WPM (that is enough to decode correct). The conclusion here is that we can achieve CW communication by lowering the transmitting power (W) if we lowering also the code speed (WPM).

From all previous formulas we can calculate the improvement of SNR in dBs of the previous example. The bandwidth of 12 WPM is 0.833x12 = 10 Hz also the bandwidth of 4 WPM is 0.833x4 = 3.333 Hz. So the improvement of the SNR (dB) from the 12 WPM to 4 WPM is SNR (dB) = 10xlog10 (BW of 12 WPM / BW of 4 WPM) = 10xlog10 (10/3.333) = 10x0.477 = 4.77 dB. This means that we can reduce the transmitting power of 10W that it was used on 12 WPM by 4.77 dB and achieve exactly the same SNR on 4 WPM. To become more precise 10 W = 40 dBm by decreasing it 4.77 dB it becomes 40-4.77 = 35.23 dBm BUT 35.23 dBm = 3.33W. Nice ha? by reducing the code speed from 12 WPM to 4 WPM we can have the same SNR by using instead of 10 Watts only 3.33 Watts (66.6% less power)!!!

Based on the fact that the majority of CW communications within HF bands take place in code speeds around 20 WPM, I used this code speed as reference and calculated the improvement in SNR (dB) for lower code speeds that go down to 600 seconds per dot (0.002 WPM):

Conclusions: Studying carefully the above table we can see that the more slower we send the more lower transmitting power we need. In my experience it is possible to have CW communications (QSOs) on 20 WPM with QRPp power lower than 1W. This means that if we reduce the speed extremely slow to 0.002 WPM (10 mins per dot) we can achieve the same distance with 40 dB lower than 1W. How much is it? It is only 100 uW (microwatts). W-O-W !!!!!!

References:
[1] Wikipedia, Morse code, http://en.wikipedia.org/wiki/Morse_code
[2] Nu-Ware, Morse code structure and timing, http://www.nu-ware.com/NuCode%20Help/index.html?morse_code_structure_and_timing_.htm
[3] ON7YD, Extreme narrow bandwidth techniques, http://www.qsl.net/on7yd/136narro.htm
[4] W5ALT, CW Bandwidth, http://www.comportco.com/~w5alt/cw/cwindex.php?pg=5
[5] Wikipedia, Signal-to-noise ratio, http://en.wikipedia.org/wiki/Signal-to-noise_ratio

Miles Per Watt in QRP

Miles Per Watt or MPW is a term very well known to QRP operators. MPW is a calculated value based on the transmitted power that was used on a single or two-way communication and the distance that was covered between the two parties. When we say one-way communication we mean the reception of a beacon and two-way we mean the QSO between two radio amateurs where each one has the capability of transmission and reception. MPW is used as unit for the measurement of the quality/importance of a communication from the transmitting power point of view.

The only things we need to calculate MPW is the distance between the transmitting and receiving location and the transmission power. The calculation of distance is a little bit complex and can be done if we know the geographical coordinates or the grid locators of the two locations. Assuming we know the distance the MPW can be calculated with the following formula:

Miles Per Watt (MPW) = Distance (Miles) / Transmission Power (Watts)

Just because the calculation of the distance based on geographical coordinates is difficult, web based WPM calculators are available online. The most popular is the "N9SSA Distance and MPW Calculator".

In this calculator you may enter latitude and longitude or the grid locator of each location and the power in Watts, you click the "Calculate Distance" button and you have all you need: Distance in Miles, Miles per Watt, Distance in Kilometers and Kilometers per Watt.

Reference:
[1] N9SSA, Notes N9SSA's Miles Per Watt Calculator, http://www.hoffswell.com/n9ssa/mpwnotes.html

Operation in QRP, QRPp & QRPpp

In amateur radio, QRP operation means transmitting at reduced power levels while aiming to maximize one's effective range while doing so. The term QRP derives from the standard Q code used in radio communications, where "QRP" and "QRP?" are used to request, "Reduce power," and ask "Should I reduce power?" respectively. The opposite of QRP is QRO, or high-power operation. Most amateurs use approximately 100 watts of power, and in some parts of the world can use up to 1500 watts. QRP enthusiasts contend that this isn't always necessary, and doing so wastes power, increases the likelihood of causing RF interference to nearby equipment etc.

There is not complete agreement on what constitutes QRP power. While most QRP enthusiasts agree that for CW, AM, FM, and data modes, the transmitter output power should be 5 watts (or less), the maximum output power for SSB (single sideband) is not always agreed upon. Some believe that the power should be no more than 10 watts peak envelope power (PEP), while others strongly hold that the power limit should be 5 watts. QRPers are known to use even less than five watts, sometimes operating with as little as 100 milliwatts or even microwatts! In brief: QRP operation is divided in three categories according to the used power. QRP means power 5 to 1 watts, QRPp means power below 1 watt to 100 milliwatts and QRPpp means any power below 100 milliwatts.

Communicating using QRP can be difficult since the QRPer must face the same challenges of radio propagation faced by amateurs using higher power levels, but with the inherent disadvantages associated with having a weaker signal on the receiving end, all other things being equal. QRPers try to make up for this through more efficient antenna systems and enhanced operating skills. QRP is especially popular with CW operators and those using the newer digital modes. PSK31 is a highly efficient, narrow-band mode that is very suitable to QRP operation.

Many of the larger, more powerful commercial transceivers permit the operator to lower their output level to QRP levels. Commercial transceivers specially designed to operate at or near QRP power levels have been commercially available since the late 1960s. As QRP has become more popular in recent years, radio manufacturers have introduced radios specifically intended for the QRP enthusiast but the majority of QRPers prefer to construct their equipment from kits or homebrew it from scratch.

Reference:
[1] Wikipedia, QRP operation, http://en.wikipedia.org/wiki/QRP_operation

What is Ham Radio

Amateur radio, often called ham radio, is both a hobby and a service in which participants, called "hams", use various types of radio communications equipment to communicate with other radio amateurs for public services, recreation and self-training. Amateur radio operation is licensed by an appropriate government entity (for example, by the Federal Communications Commission in the United States or by the Ministry of Infrastructure, Transport and Networks in Greece) as coordinated through the International Telecommunication Union. An estimated two million people throughout the world are regularly involved with amateur radio. The term "amateur" does not imply a lack of skill or quality, but rather that amateur radio and its operators work outside of an official, governmental or commercial capacity.

Although its origins can be traced to at least the late 1800s, amateur radio, as practiced today, did not begin until the early 1900s. The first listing of amateur radio stations is contained in the First Annual Official Wireless Blue Book of the Wireless Association of America in 1909. This first radio callbook lists wireless telegraph stations in Canada and the United States, including eighty-nine amateur radio stations. As with radio in general, the birth of amateur radio was strongly associated with various amateur experimenters and hobbyists. Throughout its history, amateur radio enthusiasts have made significant contributions to science, engineering, industry, and social services. Research by amateur radio operators has founded new industries, built economies, empowered nations, and saved lives in times of emergency.

Amateur radio operators use various modes of transmission to communicate. Voice transmissions are most common, with some, such as frequency modulation (FM) offering high quality audio, and others, such as single sideband (SSB) offering more reliable communications, often over long distance, when signals are marginal and bandwidth is restricted, at the sacrifice of audio quality. Radiotelegraphy using Morse code (also known as "CW" from "continuous wave") is an activity dating to the earliest days of radio. It is the wireless extension of land line (wire based) telegraphy developed by Samuel Morse and was the predominant real time long-distance communication method of the 19th century. Though computer-based (digital) modes and methods have largely replaced CW for commercial and military applications, many amateur radio operators still enjoy using the CW mode, particularly on the shortwave bands and for experimental work such as earth-moon-earth communication, with its inherent signal-to-noise ratio advantages. Morse, using internationally agreed message encodings such as the Q code, enables communication between amateurs who speak different languages. It is also popular with homebrewers as CW-only transmitters are simpler to construct. A similar "legacy" mode popular with home constructors is amplitude modulation (AM), pursued by many vintage amateur radio enthusiasts and aficionados of vacuum tube technology.

For many years, demonstrating a proficiency in Morse code was a requirement to obtain amateur licenses for the high frequency bands (frequencies below 30 MHz), but following changes in international regulations in 2003, many countries are no longer required to demand proficiency.

Modern personal computers have encouraged the use of digital modes such as radioteletype (RTTY), which previously required cumbersome mechanical equipment. Hams led the development of packet radio in the 1970s, which has employed protocols such as TCP/IP since the 1980s. Specialized digital modes such as PSK31 allow real-time, low-power communications on the shortwave bands. Echolink using Voice over IP technology has enabled amateurs to communicate through local Internet-connected repeaters and radio nodes, while IRLP has allowed the linking of repeaters to provide greater coverage area. Automatic link establishment (ALE) has enabled continuous amateur radio networks to operate on the high frequency bands with global coverage. Other modes, such as FSK441 using software such as WSJT, are used for weak signal modes including meteor scatter and moonbounce communications.

Fast scan amateur television has gained popularity as hobbyists adapt inexpensive consumer video electronics like camcorders and video cards in PCs. Because of the wide bandwidth and stable signals required, amateur television is typically found in the 70 cm (420 MHz–450 MHz) frequency range, though there is also limited use on 33 cm (902 MHz–928 MHz), 23 cm (1240 MHz–1300 MHz) and higher. These requirements also effectively limit the signal range to between 30 km–100 km, however, the use of linked repeater systems can allow transmissions across hundreds of kms.

These repeaters, or automated relay stations, are used on VHF and higher frequencies to increase signal range. Repeaters are usually located on top of a mountain, hill or tall building, and allow operators to communicate over hundreds of square miles using a low power hand-held transceiver. Repeaters can also be linked together by use of other amateur radio bands, landline or the Internet.

Communication satellites called OSCARs (Orbiting Satellite Carrying Amateur Radio) can be accessed, some using a hand-held transceiver (HT), even, at times, using the factory "rubber duck" antenna. Hams also use the moon, the aurora borealis, and the ionized trails of meteors as reflectors of radio waves. Hams are also often able to make contact with the International Space Station (ISS), as many astronauts and cosmonauts are licensed as amateur radio operators.

Amateur radio operators use their amateur radio station to make contacts with individual hams as well as participating in round table discussion groups or "rag chew sessions" on the air. Some join in regularly scheduled on-air meetings with other amateur radio operators, called "nets" (as in "networks") which are moderated by a station referred to as "Net Control". Nets can allow operators to learn procedures for emergencies, be an informal round table or be topical, covering specific interests shared by a group

Upon licensing, a radio amateur's national government issues a unique call sign to the radio amateur. The holder of a call sign uses it on the air to legally identify the operator or station during any and all radio communication. Call sign structure as prescribed by the ITU, consists of three parts which break down as follows, using the call sign SV8GXC as an example:

SV – Shows the country from which the call sign originates and may also indicate the license class. (This call sign is licensed in Greece, and is CEPT Class 1).
8 – Gives the subdivision of the country or territory indicated in the first part (this one refers to the Aegean Islands).
GXC – The final part is unique to the holder of the license, identifying that person specifically.

Reference:
[1] Wikipedia, Amateur radio, http://en.wikipedia.org/wiki/Amateur_radio