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Shortwave listening

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Shortwaves can be heard using a cheap "world band" receiver. More expensive ones come with special features, such as SSB reception.
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Shortwaves can be heard using a cheap "world band" receiver. More expensive ones come with special features, such as SSB reception.

Shortwave listening is the hobby of listening to shortwave radio broadcasts. Shortwave listeners, or SWLs, do not transmit, in contrast to amateur radio operators.

Medium quality shortwave units tend to be relatively inexpensive and easily accessible. With good radio propagation listening to remote countries' programs can be quite entertaining. Shortwave listeners also listen to ham radio operators and many hams will reply with QSL cards from SWLs. Not all but some commercial radios also reply to QSL cards.

For many listeners, the goal is to receive as many stations from as many countries as possible. Receiving stations from distant countries is also known as DXing. "DXers" as they are known, routinely test the limits of their antenna systems, radios and radio propagation knowledge. Others listen to specialized shortwave utility, or "ute", transmissions such as maritime, naval, aviation, or military signals. Others focus on intelligence signals (numbers stations). Yet others prefer listening to programs from favorite stations.

The latter may listen to specific programs, or they may listen to many programs from a few stations. Most, though, listen to shortwave broadcast stations for news and information programming.

Listeners can obtain QSL cards from broadcasters or utility stations as trophies of the hobby. Traditionally, listeners would send letters to the station with reception reports and requests for schedules. Many stations now accept E-mails or provide reception report forms on their Web sites.

Reception reports give valuable information about propagation and interference to a station's engineers. Special books with frequencies and timetables for each station, such as the annual publications World Radio TV Handbook and Passport to World Band Radio, were vital for an SWL. Today a lot of this information is available on the Internet, though the annual publications and hobbyist magazines such as Monitoring Times and Popular Communications provide many useful clues.

In addition to these traditional sources of information, hobbyists also listen to radio programs dedicated to shortwave listening, such as the U.S. based World of Radio. Many international broadcaster have hosted programs for DXers, but recently these programs have been curtailed or dropped by many international broadcasters. As of 2005, Radio Habana Cuba still hosts a program called DXers Unlimited.

Serious hobbyists may use expensive communications receivers and outdoor antennas. However, many hobbyists use less-expensive portable receivers with good results. In general any given shortwave radio will benefit from an external antenna — even a simple wire antenna — as long as the antenna is away from electrical noise sources.

There are several publications dedicated to providing information to shortwave listeners, including the magazines Popular Communications and Monitoring Times in the United States, and the annual publications Passport to World Band Radio and the World Radio TV Handbook (WRTH). In addition, stations can provide broadcast schedules through the mail or E-mail.

Contents

Future of shortwave listening

The Internet caused many broadcasters to stop their HF transmissions and begin broadcasting over the net. One of these broadcasters was the BBC World Service, which discontinued service to North America and Australasia, generating many protests and creating many activist groups such as the Coalition to [Save the BBC World Service]. It should be noted however, that the BBC is still quite audible in North America via transmission facilites on Ascension Island and Antigua.

Most of the prominent broadcasters are scaling back their analog shortwave transmissions or completely terminating them, but especially in Africa shortwave is still very common and active. Many expatriates all around the world listen to shortwave transmissions to keep in touch, even after the advent of Internet-based news and publications.

The ramp-up of digital shortwave broadcasting using Digital Radio Mondiale is giving some international broadcasters pause in their rush to completely dismantle their shortwave broadcast outlets. One reason is that digital shortwave broadcasts using DRM can cover the same geographic region with much less transmitter power — roughly one fifth the power — than traditional AM mode broadcasts, significantly reducing the electricity cost of operating a station. A traditional AM (analog) international shortwave station can have a power rating of 50 kilowatts to as much as one million watts per transmitter, with typical power levels in the 50-500 kilowatt range.

The sections below are examples of where shortwave listening is migrating rapidly into the 21st century.

Digital Radio Mondiale (DRM)

Main article: Digital Radio Mondiale
A digital mode of shortwave broadcasting is now starting to come into use. It has been approved as an international standard for digital broadcasts on the HF (shortwave) bands. A DRM broadcast rivals FM mono quality and can also send graphic images and web pages via a separate information channel. A DRM signal is typically decoded by a PC soundcard running a dedicated decoding program such as the open-source [DREAM], although receivers with built-in DRM capability are starting to appear in the market (2006).

The ITU recommends using 7 dB less power than for an equivalent analog broadcast, which means roughly one-fifth the amount of power. A DRM transmission using one-fifth the power of a current analog transmission should have a signal that is at least as good as the analog coverage.

PC controlled shortwave receivers

An important trend in modern shortwave listening is the growing use of so-called "PC radios", or radios that are designed to be controlled by a standard PC. These radios as the name suggests are controlled by specialized PC software using a serial port connected to the radio. A "PC radio" may not have a front-panel at all, and may be designed exclusively for computer control, which reduces cost. As much as 40% of the manufacturing cost of a radio is involved with the front-panel, control electronics, display and button controls#redirect . A "PC radio" is distinct from a pure SDR or Software defined Radio, which is discussed in its own section below. The PC radio in question may or may not have a front-panel and may be DSP capable. Many older radio designs dating back to the late 1980's and early 1990's came equipped with a control serial port. Perhaps the most widely used pure PC radio today, in terms of units shipped, is the Ten-Tec RX-320D, which has been continuously manufactured since 1998. Each manufacturer has created its own unique command set to control their particular radios. Software developers must then program a unique driver for each radio they want to control, a time consuming task.

Some PC radios have the great advantage of being field upgradable by the owner. New versions of the DSP software firmware can be downloaded from the manufacturer's web site and uploaded into the flash memory of the radio. The manufacturer can then in effect add new features to the radio over time, such as adding new filters, DSP noise reduction, or simply to correct bugs.

A full-featured radio control program allows for scanning and a host of other functions and, in particular, integration of shortwave databases in real-time, like a "TV-Guide" type capability. This is particularly helpful in locating all transmissions on all frequencies of a particular broadcaster, at any given time. The most widely used free shortwave database is provided by a German company at [ILGRadio].

Some control software designers have even integrated [Google Earth] to the shortwave databases, so it is possible to "fly" to a given transmitter site location with a click of a mouse. In many cases you can actually see the transmitting antennas where the signal is originating from!

Features of shortwave radio control software

The field of software control of PC radio's has grown rapidly in the last several years, with developers making a number of advances. Since the Graphical User Interface or GUI interface PC to the radio has unlimited flexibility, any number of new features can be added by the software designer.

Here is a partial list of features that can be found in advanced shortwave control software programs today:

Software-defined radios

Main article: Software-defined radio
The next level in radio / software integration are so-called pure "software defined radios". The distinction here is that all filtering, modulation and signal manipulation is done in software, usually by a PC soundcard or by a dedicated piece of DSP hardware. There may be a minimal RF front-end or traditional radio that supplies an IF to the SDR. SDR's can go far beyond the usual demodulation capability of typical, and even high-end DSP shortwave radios. They can for example, record large swaths of the radio spectrum to a hard drive for "playback" at a later date. The same SDR that one minute is demodulating a simple AM shortwave broadcast may also be able to decode an HDTV broadcast in the next.

A well known open-source project called GNU Radio is dedicated to evolving a high-performance SDR. All the source code for this SDR is freely downloadable and modifiable by anyone.

DSP technology

DSP technology, short for digital signal processing, is coming into wide use in modern shortwave receivers. The primary benefit of DSP hardware in shortwave receivers is the ability to tailor the bandwidth of the receiver to current reception conditions and to the type of signal being listened to. A typical analog only receiver may have a limited number of fixed bandwidths, or only one, but a DSP receiver may have 40 or more individually selectable filters.

Under good band conditions with no adjacent channel interference, a wide bandwidth (i.e. 8 KHz or better) can produce quite pleasing shortwave audio reception. Under noisy band conditions the operator might want to shift to USB (i.e. upper sideband) mode or LSB mode (i.e. lower sideband) and a narrower DSP filter for improved reception. All AM modulated signals have the property of having both sidebands carry audio information. So a standard AM signal actually is three channels in one! There are many other simple "tricks of the trade" in shortwave listening that can dramatically improve reception results. Another technique is "diversity reception", which is having two or more antennas that can be switched in or out in a type of "A to B" comparison to see which one provides the best signal.

The standard shortwave receiving antenna is the dipole antenna which can be readily purchased or made by hand from a roll of wire and a couple of insulators.

See also

Literature

External links

 

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