MW DX

Key takeaways

MW DX belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect MW DX to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of MW DX from memory before moving on to harder problems.

Reference excerpt

MW DX, short for mediumwave DXing, is the hobby of receiving distant mediumwave (also known as AM) 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 – 1710 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, radio propagation, and reception techniques.

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 weakens, allowing medium wave radio waves from such stations to bounce off the F layer of 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 allow reception of different stations at different times - for example, on one night a medium-powered broadcaster from Cleveland, Ohio may be audible in Duluth, Minnesota, 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, along with sunrise and sunset ("SRS" and "SSS") periods when DX stations appear on and disappear from the dial. 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 miles away is possible even far inland, but may require exceptionally good conditions and a good receiver and antenna on the listening side.

MW DX in North America In the United States and Canada, stations on the mediumwave dial are spaced at 10 kHz intervals from 520 to 1710 kHz as prescribed since 1941 by the North American Regional Broadcasting Agreement. 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 Class C "graveyard" frequencies where many lower-powered stations operate). The most powerful stations in the two countries are clear-channel stations which can transmit with 50 kilowatts of power. Examples of stations in this category from the List of clear-channel stations are: WLS in Chicago on 890 kHz, KMOX in St. Louis on 1120 kHz, WSB in Atlanta on 750 kHz, WCCO in Minneapolis on 830 kHz, WWL in New Orleans on 870 kHz, CJBC from Toronto on 860 kHz, WABC in New York City on 770 kHz, WLW in Cincinnati on 700 kHz, WHSQ, 880 kHz in New York City, and WTAM in Cleveland on 1100 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, several Mexican stations can be heard. Many of these are called Border blaster stations because they program in English to reach the American market. Some of these operate with over 100 kW of power with highly directional antennae aimed northward to avoid interfering in the rest of Mexico. Many can be heard on a similar night-to-night basis. Many of these stations are also treaty allocated clear-channel stations, ensuring that there will be no interference or limited interference on the same frequency. Although some distant listeners may rely on such stations for non-DX purposes, such as to hear a certain talk show 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 miles under certain instances. Similar are the tiny radio stations operated by high schools. On the East Coast of the United States, 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 of the US 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 AM expanded 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 spectrum, with the first two applications for frequencies having been granted in 1997. 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.

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with MW DX

Start with the simplest possible case. Write down what MW DX claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to MW DX before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about MW DX ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of MW DX

In research: MW DX appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses MW DX in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: MW DX is common in secondary-school and first-year university syllabi. It links to neighbouring topics Radio frequency propagation, Radio hobbies, so understanding it makes those chapters shorter.
In everyday life: Look for MW DX outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study MW DX in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what MW DX means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain MW DX out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is MW DX in simple terms?

MW DX, short for mediumwave DXing, is the hobby of receiving distant mediumwave (also known as AM) radio stations. MW DX is similar to TV and FM DX in that broadcast band (BCB) stations are the reception targets.

Why does MW DX matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study MW DX?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on MW DX.