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CQ DX for an SWL Introduction (I)
How to proceed to listen in the best conditions to amateur radios working from another continents, the famous DX stations ? Don't tell me to switch on my receiver, Hi! As you will quickly understand, it is not obvious to answer simply and in a few words to this question. More, it does not only interest SWLs (short waves listeners) but licensed amateurs too. Indeed, before working a DX station any amateur must first of all be able to listen his correspondent before to say like some do without listening at their contact "59, QSL ?"... However the problem is more hard to solve for as SWL as he or she is only listening ham bands and cannot initiate a QSO in calling "CQ DX". When I was SWL (and once licensed as well) using a dipole or even a small vertical, I received quite weakly signals emitted by DX stations. So, I tried to understand why I received them in such conditions, and I tried to find a way to solve this problem. I quickly noted that many factors could affect and ruin all my chances to listen or work DX stations, although both situations are not exactly reciprocal. We will come back on this difference when we will speak about wire antennas for listeners. At the time I was a novice SWL, I encountered many difficulties to find the information in order to optimize my way of working. I had to find by myself the documentation and papers explaining the how and why of things. I had to subscribe to magazines and clubs, contact ham friends, experiment by myself, to finally find the answers and understand what happened on the air. As I spend years to understand all this, to not lose all this knowledge, I decided to share all I learnt with you. So, I dedicate this article to all SWL and novice licensed hams who wish to get the most of their equipment and profit at best of propagation conditions. The following recommendations are based on my humble and own experience of listener that extended over several years, and after have participated in a few contests (e.g. confirmed 87 entities in 43 hours of operation using a simple longwire antenna, 65 entities during a CQ WW contest, or confirmed more than 250 entities in one year of activity) before to get my license and the DXCC award. How optimizing your DX chasing If it is quite easy for a licensed ham radio working in HF to send a "CQ DX" to a far country and waiting for a contact, for a listener there is no other solution than scanning continuously bands and regularly QSY in search of the most wanted call signs, with or without the assistance of clusters. Of course licensed amateurs are also confronted to this problem and some others. Indeed, it is not enough to call "CQ DX" if there is nobody to answer you on the other side of the Earth or if your antenna system does not allow you to pick up efficiently the signal of your remote correspondent ! There are thus several ways to optimize your chasing of DX stations and to pick up interesting QSOs. Here is a non-exhaustive list of factors that can affect your results or that will help you improving them : Limiting factors - Specifications of your receiver - Your antenna system - Your location and working conditions - Levels of solar and geomagnetic activities - The band that you work - The day and time of the year - The MUF and its impact on DX transmissions Improving factors - Check beacons - Take advantage of the gray line - Take advantage of time zone shifts - Take advantage of short and long paths - Listening to DX networks - Listen to CQ WW contest - Chasing DXmen - Connect you to clusters and use packet radio - Check DX news. We are going to review each factor and how it determine your chances to hear a DX station. Specifications of your receiver Shortwave receivers (or even transceivers) doesn't show all the same performances. For a listener the most important parameters of a receiver are its sensitivity and selectivity. The sensitivity represents the minimum input signal required to produce a specified output signal. Under this threshold you listen only to the electronic noise of components (thermal, shot, flicker and burst noises) or, at best, the electromagnetic noise from the environment (artificial and natural noise) on the frequency but no readable signal. The second quality factor concerns the selectivity of your receiver. It represents its ability to respond to a tuned station and to reject any nearby undesired interference or noise, or both. This is probably the first feature where your receiver will show its performance. The next one will be the performance of its digital signal processing (DSP). If you need more information about this subject, I suggest you to read my page entitled "How to select an HF transceiver" and specially the paragraph about the selectivity as it plays a very important role in receive. Your antenna system If the sun is the major source of QRN on frequencies after the ionospheric perturbations, whatever the index of the solar activity, your chances to capture amateurs transmissions depend first of all on the type of antenna used, its length, its properties (radiation pattern, gain, coupling, etc) without to mention propagation conditions.
As we told, to hear and to work a DX station are two very different activities. A licensed OM or YL needs to concentrate all the input signal in a narrow beam to be sure to reach his or her correspondent. But for a listener, often using a poor antenna system (an indoor antenna, a dipole tight 5 m high outdoor or a small vertical), the antenna plays a passive role, excepted for the few SWLs than can pay for a directional antenna (beam or quad). However, there is one rule to remember : the longer will be your antenna driven element the better will be the receive. In fact, your receiver will be more or less able to capture weak signals according to your antenna design and its radiation pattern. For example, a long wire cut for the 20 m band placed too low over ground (say 2 m high) or showing a length of 1l only will show a bidirectional pattern and two main lobes while it will show many additional lobes if it is tight 7 or 10 m high or if its length exceeds 5l as displayed on this graph. A similar change occurs for a vertical depending if it is cut at 1/4l or 5/8l as displayed on this graph. If you have installed a small vertical antenna in your garden, the amateur using a very directional beam placed 15 m above ground will work in conditions far better that yours and his/her installation will react much differently from yours to the ground effect and interferences (mainly true for emissions). Directional antennas are the most suited for DX chasing due to their directivity and ability to reject noise (using beams or quads, a front-to-back ratio exceeding 20 dB is common). But if you cannot avoid or reduce noise and RFI, sometimes you have no other choice than waiting that the night falls to hear the world traffic from Canada to Chile via Australia and South Africa among other DX. This is mainly true at spring and summer or during the maximum of the solar activity. Practically, if I check my log during a cycle of high solar activity, I nearly interrupted listenings HF bands between 8 a.m.-6 p.m local time on summer due to the QRN. Of course when propagation was widely open in summer at daytime, by 3-5 p.m. local time I already heard loud and clear far stations from countries like DU, JA or Z2 on the 20 m or 15 m band, but compared to the number of stations I captured in the summer at night, at daytime it is sometimes like working near a pneumatic drill ! But the sun is not the only responsible of all these noises and many signals have a man-made origin, from computers to power lines or transformers. We will take time to discuss of this problem in another page dealing with RFI. If you are unable to modify your antenna system (for technical or financial reasons, or both), you can still optimize your chances to hear DX stations because other factors have to be taken into account. Your location and working conditions HF shortwaves at wavelenghts between about 40 and 10 meters, need free space to propagate, I mean that they can be influenced by hills or small valley. From a waves propagation point of view, it is obvious that you will have troubles in trying to listen to far DX stations from the bottom of a steep-sided valley. If your HF antenna is unable to capture waves travelling a few hundreds of meters higher than the roof of your house, it is useless to install a shack at this location. Better to go mobile and to reach the top of the hill to capture these shortwaves. Of course, the longer will be the working wavelength (80 or 160 m), the easier will be its capability to jump over obstacles and reach your shack located at the bottom of the valley or behind a hill. Contrary to a beam polarized horizontally, a vertical antenna is vertically polarized. This latter is thus not entirely able to discriminate signals from the noise, and will capture all local noises as strong as the signals from far emitters. As explained above, during high solar activities and the summer months, you should wait until the evening and the sunset to hear your favorite DX stations. At last, you can also change your working mode and listen amateurs working in CW (even if you need a Morse translator to understand the traffic). Not many amateurs like this mode but it is still the best to pass through QRM or QRN and to capture (or reach) the farest DX stations. Solar and geomagnetic activities
You will find in the French pages of this site devoted to the solar system a thorough study of the sun activity thanks to the collaboration of NASA and SOHO scientists. In a few words we can say that the 11-year sunspot cycle determines radio amateurs activities on bands, and thus your chances to hear DX stations. When the sun is in a period of high activity like in 2000-2002, the low frequencies (below 10 MHz) become less usable due to absorption while higher ones become more suited for DXing. Conversely, when the sun is in a quiet period six years later, with practically no sunspots on its surface, at daytime lower frequencies are more longer open to DXers. So in 2000, at the paroxysm of the solar activity, where the sun displayed over 300 individual sunspots some of them visible naked eye like on the picture displayed at right, thanks to an intense solar flux (SFI of 169, SSN of 125) ionizing upper bands (21-30 MHz), many stations 10000 km away were accessible without too much difficulties 24 hours a day. Effects of the solar and geomagentic activities on the ionosphere are very complex. Tens of perturbations have been identified. Not only the solar flux affects directly the concentration and height of ionospheric layers, but solar particle emissions (CME, X-flare with fast electrons and heavy protons, ions, etc) are also involved in geomagnetic disturbances like fading, blackouts, sudden ionospheric disturbances (SID), polar cap absorption (PCA) and the famous auroras and associated events. All these disturbances affect sky waves propagation and thus the ability of your antenna to pick-up signals of DX stations. See the previous hyperlink for more detail. Select the right band When the solar flux is high with low geomagnetic activity, bands are usually wide open to low powers. In such conditions you will discover that radio amateurs work 24 hours a day 365 days a year on most bands, including on the top band (160 m) at night. With over one million active radio amateurs around the world (for more the three millions licensed), you have many opportunities to hear them here and there. But some bands are more crowded than others, and weekends more than week days. Even if that seems trivial, do select the most active band according to the season and the time of the day of your listening. Indeed, it should be an absurdity to listen a band that all hams known to be close, e.g. the 20 m band in winter late in the afternoon when the sun is quiet or during blackouts at spring. For sure you will hear some QSOs, probably local or some powerful emitters working with 1 kW and gain antennas, but the rate of QSOs in that band will be most that probably very low compared to the listening of the same band during the summer eve's and in a time of solar maximum activity. The skip distance There is also another reason that could explain that you don't hear many amateurs on the air : the skip distance. It is a silent zone that essentially affects short distance contacts (mainly between 300-2000 km or so). If you do not take care to the way that shortwaves travel in the ionosphere, according the distance to your correspondent, your working frequency and propagation conditions you will be able or not able to hear QSOs between your neighbours; signals enter the ionosphere and escape to space or, if they reflect to the ground, you can experiment a signal loss over 25 dB or even a complete extinction. In fact there is no skip distance as long as the working frequency is less than the critical frequency of the concerned layer. In addition the skip distance shows the same variations associated to that critical frequency (diurnal, seasonal and solar cycle).
Hopefully, in the lower bands of 160 and 80 m, the waves are so long that there are no skip distance or silent zone around any emitter. In the 40 m band there is no skip distance excepted at night where it can extents up to 500 km. In the 30 m band the skip distance reaches 300 km at daytime and about 1000 km at night. Therefore in small states QSOs with border countries can be hard to work. In the 20 m band the skip distance reaches 700 km at daytime and can exceeds 1600 km at night. On the 17 m band the skip distance reaches 1200 km at daytime, it is of 1300 km on 15 m at daytime, 1600 km on 12 m and up to 2000 km on 10 m, only at daytime. This phenomenon explains why all local QSOs and mobiles activities are most practiced in the lower bands of 40, 75, and 80 m, where you can easily heard your friends living a few tens or hundreds of km away, work castels, lighthouses and other national islands, but even in these bands first dedicated to "local" activities, DX can be worked in winter, at night or using the grayline as we will see later. The day and time of the year To select the "right band" infers that you take into account the cycle of light and darkness as well as the cycle of seasons to increase you chances to capture DX entities. The 24-hour cycle produces a major effect on all shortwaves (to 10 m). A good rule is to say that both extremes of the HF spectrum are very sensitive to the time of the day. As listed in the next table, we can say that wavelengths above 30 m (frequencies below 10 MHz) are best at night and wavelengths below 30 m (above 10 MHz) are best at daytime.
You have probably also discovered that from Europe you cannot hear W6 stations, located on the Western US coast, when you hear quite well K1 stations in NJ and sometimes the ones located in the Midwest; at other occasions you can hear ZL and VK on mornings using the gray line (see next page) but with much more difficulties a few hours later; at last when you can hear PY it is very difficult to listen to UA9 stations. The problem is still worse in the lower bands : when bands are wide open up to 10m, the lower ones, 40m and below can stay close. In fact this factor is mainly directed by the degree of ionization of the D and E-layers, thus related to the Sun position over the Earth. Do observe openings in the propagation during a few days in summer. First bands open to UA0, then JA, ZL, VK, UA9, VU, ON, ZS, VY, K1, PY, W6, KH,...). Ask to a close licensed friend using a directional antenna to try calling a JA station when the opening is toward VK, there is few chance that he succeeds. Ask him to call a VK when the Sun is over PY : he will work VK with much difficulties or will fail. But when it is noon in VK he might work him quite easily. So you have a confirmation that openings follow strictly the Sun position over the Earth. So, if your hear some JA, UA9 or VU stations you know now that you will not hear at the same time K1, YV or PY stations. Then the time of the year affects the amount of light or darkness on the earth (excepting at equatorial latitudes). In winter as the days are much shorter, wavelenghts above 40 m (7 MHz and below) open more and more earlier and gather most of amateurs. If you can also hear DX stations on upper frequencies (between 21-30 MHz) during winter time and high solar activity, these bands will unfortunately close very soon, following the sunset (at 4:30 or 5 pm local time). Conversely, in summer while the days lengthen propagation allows to work on shorter wavelengths, all night long if necessary, always during periods of high solar activity. Your working frequency will thus change according to the time and season of the year. This practice is also used by broadcasters transmitting in HF bands; depending on the time of the year these emitters change their frequencies so that they can reach their audience at best, with a strong signal and more than 90% of reliability At last as we introduced above, the possibility to hear or to work a station is determined by the critical frequency of ionospheric layers, and especially by the Maximum Usable Frequency, the MUF. Next chapter The MUF and its impact on DX transmissions
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