MW DX

From Wikipedia, the free encyclopedia

Drake R8B communications receiver. The R8B is a popular receiver for MW DX.
Enlarge
Drake R8B communications receiver. The R8B is a popular receiver for MW DX.

MW DX, short for mediumwave DXing, is the hobby of receiving, or simply the reception of distant mediumwave (known outside radio circles as "AM radio" in North America) radio stations. MW DX is similar to TV and FM DX in that broadcast band (BCB) stations are the reception targets. However, the nature of the lower frequencies (530 - 1700 kHz) used by mediumwave radio stations is very much different from that of the VHF and UHF bands used by FM and TV broadcast stations, and therefore involves different receiving equipment, signal propagation, and reception techniques.

Contents

[edit] Propagation

During the daytime, medium and high powered mediumwave AM radio stations have a normal reception range of about 20 to 250 miles (32 to 400+ km), depending on the transmitter power, location, and the quality of the receiving equipment, including the amount of man-made and natural electromagnetic noise present. Long-distance reception is normally impeded by the D layer of the ionosphere, which during the daylight hours absorbs signals in the mediumwave range.

As the sun sets, the D-Layer dissipates, allowing Medium Wave radio waves from such stations to bounce off the ionosphere, producing reliable, long distance reception of (especially) high-powered stations up to about 1,200 miles (2,000 km) away on a nightly basis. Aside from the more or less regular reception of certain high powered transmitters, variable conditions although reception of different stations at different times - for example, on one night a medium-powered broadcaster from Cleveland, Ohio may be audible in Duluth, but not on the following night. Much of the hobby consists in trying to receive and log as many of these stations as possible, identifying target stations and frequencies to listen to and log.

Near or on the coastlines, trans-oceanic reception is quite common and a favored target of DXers in those areas. Very distant inter-continental DX from stations several thousands of kilometers distant is possible even far inland, but may require exceptionally good conditions and a good receiver and antenna on the listening side.

DX stations evaporate from the dial as the sun rises. However, sunrise and sunset ("SRS" and "SSS") periods can provide interesting loggings.

[edit] MW DX in North America

In the United States and Canada, stations on the mediumwave dial are spaced at 10 kHz intervals from 530 to 1700 kHz. The tremendous number of radio stations in this region of the world and limited number of available frequencies means congestion is very common, and DXers may hear two, three, or more stations on the same frequency (especially on certain "graveyard" frequencies where many lower-powered stations operate). The most powerful stations in the two countries transmit with 50 kilowatts of power. Examples of stations in this category are WLS in Chicago on 890 kHz, WTMJ in Milwaukee on 620 kHz, WSB in Atlanta on 750 kHz, WCCO in Minneapolis on 830 kHz, and CJBC from Toronto on 860 kHz, all of which can be heard over much of the United States and Canada east of the Rocky Mountains. In the southern half of the United States, Mexican stations, some of which operate with over 100 kW of power, may be heard on a similar night-to-night basis.

Although some distant listeners may rely on such stations for non-DX purposes, such as to hear a certain talk show (although this is becoming less popular with the continued homogenization of radio stations) or sporting event, DX'ers generally log these stations when they begin the hobby and afterwards pay little attention to them while seeking out new, less powerful and well-heard stations, often with a few kilowatts of power or less, or unusually distant stations. Especially prized in the former category are receptions of distant traveler information service (TIS) stations, operated by the Department of Transportation to give visitors information. These stations typically run at very low powers (limited to 10 watts) and are only intended to cover small areas, but may travel thousands of kilometers under certain instances. Similar are the tiny radio stations operated by high schools.

On the East Coast, it is not unusual for DX'ers to hear the high-powered European stations, which operate at 9 kHz intervals, rather than the 10 kHz in the United States, helping to reduce co-channel interference from domestic stations, from countries such as Spain and Norway. Stations from Africa and the Middle East are also often heard. The Pacific Coast provides a similar opportunity with stations from Asian countries and Australia / New Zealand although a considerably longer distance must be covered. On both coasts, as well as in the middle portion of the country, "Pan-American" DX from Latin American and Caribbean nations is often sought and logged.

The expanded AM band, or "X-Band" as MW DXers often call it (not to be confused with the range of microwave frequencies), runs from 1610 kHz to 1700 kHz. This is a relatively new portion of the mediumwave broadcast, with the first two applications for frequencies having been granted in 1997 [1]. The lower density of stations in this area of the spectrum, as well as a lack of stations with more than 10 kW of power in the United States, has led to many DX'ers taking interest here.

[edit] MW DX in Europe

Stations in Europe often run higher power than American stations, sometimes several hundreds of kilowatts. Synchronous networks are also commonly used, with local transmitter stations often having less of an identity than those in the United States and Canada. The wide variety of languages spoken over the DX'ing range, from Spanish to Arabic to Estonian, adds an element of challenge to DXing in the region. Some stations in Europe have taken to Digital Radio Mondiale transmissions, requiring a receiver capable of demodulating such signals, or a computer loaded with special software coupled to the receiver.

DX reception of North American stations has been observed on many occasions. CJYQ (St. John's, Newfoundland and Labrador) 930 kHz is regarded as the easiest to receive, and its presence is taken as an indication that the reception of more distant stations is possible. North American stations whose frequencies are furthest from the 9 kHz multiples used in Europe are easier to receive, particularly since 24-hour broadcasting is now the norm in Europe.

[edit] Equipment

While any radio covering the mediumwave (AM radio) band can be used for DX purposes, serious DXers generally invest in a higher-quality receiver, and often a specialised indoor tuned box loop or outdoor longwire antenna. At the lower end of the spectrum, a portable radio with its own internal ferrite core antenna designed for long-distance AM radio reception may be used, such as the venerable GE Superadio. More serious DXers may upgrade to a high-quality shortwave communications receiver with good performance on the lower mediumwave frequencies, such as the Drake R8 or AOR 7030+. In such a configuration, a high-performance indoor loop or outdoor longwire antenna, sometimes many hundreds of meters long, depending on space availability, is normally used. For trans-Atlantic or trans-Pacific reception, where the target station is on a 9 kHz rather than a 10 kHz multiple or vice versa, receivers with narrow RF filters are useful in order to exclude adjacent broadcasts on the listener's own continent. To combat noise, DXers may use an outboard noise attenuation device, or a radio with built-in digital signal processing capabilities. A personal computer with specialized logging software or simply a paper notebook is used to write logs. Tape recorders can be used to archive memorable DX moments, or identify hard-to-hear station receptions after the fact.

[edit] See also

[edit] External links

Retrieved from "http://en.wikipedia.org../../../m/w/_/MW_DX_441f.html"