Tropical Band DXing
The Where, When, Why, What, and How
By Don Moore
WHERE ...are the tropical bands? According to the rules, there are three distinct ranges: 2300 - 2495, 3200 - 3400, and 4750 - 5060 kilohertz. Long-standing international agreements have set aside these frequencies for broadcasting stations located between the Tropics of Capricorn and Cancer. Most, but not all, countries strictly adhere to these guidelines. The most common exception is "out of band" broadcasting where stations use adjacent frequencies allocated to other types of radio services. For example, there are several dozen tropical band stations in the 5200-5700 kHz range. In some countries, such as Vietnam and Indonesia, these are official government stations. In others, Peru and Bolivia especially, private broadcasters in remote areas simply ignore the regulations and the government does not have the manpower, funding, or interest to stop them. Thus, for all purposes, the tropical bands may be thought of as anything between 2000 to 5900 kHz. Furthermore, there are many smaller stations through 7500 kHz that can just as well be considered tropical band broadcasters.
The second exception is that not all tropical band stations are in the tropics. For decades, China and Russia have had numerous stations in the tropical bands. One old Soviet tropical band station was actually located in Murmansk, north of the Arctic Circle! More recently, some US-based shortwave broadcasters have used loopholes to get FCC permission to broadcast in or just outside the tropical bands. So, tropical band stations are not necessarily tropical.
WHEN ...can the tropical bands be DXed? The key word here is darkness. The lower shortwave frequencies only propagate long distances when most or all of the reception path is in darkness. For the listener, that means from about two hours before local sunset to about two hours after local sunrise. (The station heard must also be in or near darkness.) Right now, in mid-winter, there are less hours of daylight than at any time of year, which means more hours when tropical band DX can be heard. Conversely, June provides the fewest hours of listening. Nicely enough, static levels are also at their lowest in mid-winter (and highest in June), which means we are at the beginning of the best tropical band DX time of the year.
Because of the need for darkness, there are particular time periods, or windows, each day to listen to tropical banders from different regions. Because Latin America is south of North America, it is the simplest. Any time it is dark or near dark at your location you can probably hear some Latin American stations. However, most stations sign-off by 0400 UTC and few sign-ons begin before 0900, so there isn't much to be heard in the middle of the night.
There are two windows for hearing African stations. The first begins an hour or two before sunset at the DXer's North American location and lasts until about 2400 UTC, at which point almost all African stations have signed off for the night. (Eastern Africans begin the sign-off parade about 2000 UTC.) The further west the listener is located, the shorter and later this window is. On the west coast, there is no first window at all. The second window starts at 0300 when the East Africans begin to come back on and lasts until sunrise at the transmitter site. As morning moves across Africa from east to west, more stations sign-on. They may be heard for an hour or so until their local dawn catches up with them. The last stations, in West Africa, fade out around 0700 to 0800, depending on the time of year. While this second window is open to all North America, signals are usually weaker as one moves towards the west coast.
The third main target area is East and South Asia and the Pacific, for which there is one main window in the morning. After darkness covers the west coast, it gradually moves across the Pacific, creating darkness reception paths as it goes. This target area is - from Australia to Mongolia, and from Pakistan to Vanuatu - so there is a lot of variation both geographically and seasonally. But generally speaking some part of region is within the darkness path to North America between 0800 to 1500 UTC. Of course, because of the North American sunrise, East coasters have the shortest window, ending about 1200 UTC, and West coasters have the longest (and strongest signals). During the winter months, however, East coasters (and, to a lesser extent, Midwesterners) do get the benefit of a late afternoon window to parts of east and south Asia at around 2100 to 2200 UTC.
Of course, nothing is quite that simple as just listening during those windows. Tropical band reception tends to be best during grayline enhancement. What's that? Just a fancy word for sunrise or sunset. We'll skip the technical background, but the ionosphere gets extra-excited when it is changing from light to dark or vice-versa. If either the listener or the station is at sunset or sunrise, reception is enhanced. If both the listener and the station are on the grayline at the same time, WOW! However, between any two specific points, that does not happen very often. For example, Iowa and Bolivia are both on the grayline at about 1100 UTC in mid-June and about 2230 UTC in mid-December. The when and where of graylining can be determined through software such as GEOCLOCK, paper maps which some DX clubs sell, or other tools such as the slide-rule like DX Edge.
WHY ...do DXers go after stations on the tropical bands? The biggest reason is the challenge. Because most tropical band stations are broadcasting just for listeners in their own country, transmitter powers are usually low. Few are over ten kilowatts, many under one kilowatt. International broadcasters with 500 kW just don't present that kind of challenge! And, unlike the big guys, few tropical band stations have antennas that maximize low angle distant propagation. Antennas are either designed for high-angle, relatively local coverage or are haphazardly put up without any plan at all. Many small Andean stations just string a wire between two trees and don't even bother to match it to the transmitter! Throw in some static and fading, and you have the biggest DX challenge the shortwave broadcast bands have to offer.
The other reason to DX the tropical bands is who can be heard. For a variety of reasons, the tropical bands are not the best place for long-distance propagation of radio signals. That's not to say, you can't hear distant stations on the tropical bands - far from it! But, if you are a major international broadcaster and you want to get a good solid consistent signal into your target area every day, the higher frequencies work better. So there is very little international broadcasting in the tropical bands.
However, most of the world's countries do not have an international broadcasting voice with English programs for overseas listeners. But, most do have some sort of domestic broadcasting on shortwave, usually in the tropical bands. It is impossible to log more than about seventy or eighty countries without DXing tropical band stations. With the tropical bands, many DXers have heard over 200 countries and over 1000 stations.
Finally, there is the programming, which is a lot different from international broadcasters. Because most tropical band stations broadcast to their own country, this is a chance to hear real local radio from around the world. It may not always be professional, but it has an authentic quality that has disappeared from much of the homogenized US. radio dial. Of course, most broadcasts will be in a language other than English. If you know a little Spanish or French, that will be help. However, many things to be heard on the tropical bands transcend the language barrier. For example, there's nothing like the excitement of a Brazilian futbol (soccer) announcer - it's easy to feel the atmosphere even without knowing a word of Portuguese. (And wait to you hear your first "goo - insert one thousand o's here - oal" scored!) Of course, music overcomes any language difference and for good international music, the tropical bands can't be beat.
WHAT ...equipment is needed? Any receiver that includes the tropical frequency range will pick up at least a few stations if conditions are right. A few years ago, I picked up several Latin American stations on a cheap three-band portable costing less than $30. But real DXing does take a better receiver. The minimum is a good portable, like the Sony ICF-2010 or Sangean ATS-909, and a good tabletop receiver like the Drake R-8 series or the AOR AR-7030 is better. The keys to receiver choice are sensitivity and selectivity. The receiver must be sensitive enough to make usable audio out of signals that are sometimes very weak. Selectivity - the ability to cut out nearby interfering signals, or QRM - is just as important. Like the international bands, the tropical bands can also be congested at times. On the international bands, at least the interference is almost always 5 kHz away, since stations are on frequency. But, some tropical band stations drift in frequency, so the QRM might only be two or three kilohertz away! And, besides QRM from other broadcasting stations, digital utility stations - RTTY, morse code, FAX, etc - also use some of the tropical spectrum.
Good selectivity is just the first tool that DXers can use in cutting down interference on the tropical bands. Many DXers do much of their tropical band DXing in SSB mode, even though the signals are AM, not SSB. The reason is simple. If you are listening in Upper Side Band (USB) mode, you hear only what is above, not below, the frequency you are tuned to, which eliminates or at least reduces QRM from a lower frequency. Use Lower Side Band (LSB) mode to reduce QRM on a higher frequency. Either way, with SSB you have to tune in the station precisely. If you are off by even a hundred Hertz, the signal will be distorted and there will be a sharp tone. This type of tuning takes practice, but it's well worth it. Try it on some strong signals first, to develop your touch for the weak ones. Other tricks include use of things like the tone control, notch filters, synchronous detection, and passband tuning, if your receiver has those. Controls which are not often needed for the big broadcasters come in very handy on the tropical bands.
Of course, a receiver is no better than the antenna it is attached to. An outdoor wire antenna is a near-must for tropical band DXing. Beverage antennas - several hundred feet of wire strung in a straight line about eight feet above the ground - are DX nirvana, but for most people they are only practical on DXpeditions. However, small active antennas and indoor loops can be almost as good, if they are located in a quiet environment. I continue to have very good results with my twenty-year-old ferrite bar loop, which easily sits on top of my desk.
In depth information about buying receivers, and using specific antennas is beyond the scope of this article. For more specific facts about receivers, check Larry Magne's reviews in MT and Passport to World Band Radio. There are several good antenna books on the market; I especially like the ones by Ed Noll and by Joe Carr. And remember, while equipment is great, plopping down $1000 for a fancy tabletop receiver doesn't make anyone a good tropical band DXer. An experienced DXer with a ICF-2010 will outhear a novice with an R-8B any day.
HOW ...can you become a good tropical band DXer? Learn the bands. That's why an experienced DXer with minimum equipment will outhear a novice with the best. The experienced DXer knows what is usual and what is unusual. When tuning the bands, he will stop for a few seconds with each station found. Based on the frequency, language, programming, signal quality, and time of day he will know who most stations are - the usuals. If something is different, that will stick out. Perhaps there is a new or rare station on a usually empty frequency. Maybe Spanish language and Guatemalan music is heard on a frequency that had been occupied by a Brazilian broadcaster. Maybe a usually weak but regular African station is booming in, indicating enhanced conditions to that region and a chance to go after less common stations.
There is no magic to successful tropical band DXing. The longer one pursues the hobby, the more experience is gained and the better the DXer becomes. Gradually, the DXer learns to recognize major DX languages such as Spanish, Portuguese, Indonesian, Russian, and French. Then he learns typical phrases that are used with station IDs, time checks, and other important announcements. Recognizing music types is just as important. Few stations outside Indonesia play gamelan music. To the novice, African rhythms and Latin American tropical music may sound much the same, as might Chinese and Andean music. Yet, each are very distinctive. With experience, DXers learn to recognize different types of African music and even the difference between northern and southern Peruvian huaynos.
Just as important is the DXer's general background knowledge of the DX target area. Knowing the names of countries, cities, rivers, and other geographic features may help. Some DXers can list from memory the names of many of the internal states or departments of Peru, Bolivia, and Brazil. Other important clues include the names of the local currency, the president and prominent leaders, and major consumer products. (Beer and banks are two of the most widely advertised products on Latin American radio. The company name can narrow down which country is being heard.) All this is learned over time.
One part of the road to experience is simply putting in the time at the dials. The other is using references and resources. Regularly reading DX bulletins and radio websites is a must, as is having a good atlas. Borrowing library books and videos on a favorite DX target area can not only be interesting, but can help the DXer learn helpful background knowledge. Many libraries have CDs of international music as well. Also, try finding soundclips from world music vendors on the Internet. In the end what the DXer knows or knows where to find is what counts.
So, isn't time to begin your own tropical band memories of best catches, favorite QSLs, and early morning listening sessions? And, who knows. You might even hear some calypso music!
BEST BET TROPICAL BAND STATIONSTwenty-Five of the Best Heard Countries in North America
|2325||Australia||VL8T Tennant Creek|
|3290||Namibia||Namibian Broadcasting Corporation|
|4753||Indonesia||RRI Ujung Pandang|
|4755||Brazil||Radio Educacao Rural|
|4770||Nigeria||Radio Nigeria, Kaduna|
|4835||Mali||Radio Television Malienne|
|4890||Papua New Guinea||National Broadcasting Commission|
|4926||Bolivia||Radio San Miguel|
|4980||Venezuela||Ecos del Torbes|
|4990||India||All India Radio|
|5030||Costa Rica||Radio Lira|
|5125||China||China National Radio|
|5500||Ethiopia||Voice of the Tigrey Revolution|
This article is copyright 1998 by Don Moore. Not to be reproduced without permission.
This website is maintained by Don Moore,
Association of North American Radio Clubs
DXer of the Year for 1995.