- Shortwave listening
Shortwave listening (abbreviated as SWLing) is the
hobbyof tuning for shortwave radiobroadcasts located on shortwave frequencies, usually thought of as those from 1700 kHz(the upper limit of the AM broadcastingband) to 30 MHz(the lower limit of the tuning range of most scanner radios). cite web|url=http://www.dxing.com/swlintro.htm |title=Introduction To Shortwave Listening |accessdate=2007-11-21 |work=DXing.com |publisher=Universal Radio Research ]
Listening to shortwave broadcast stations for
newsand information programming is common, but for many shortwave listeners (abbreviated as "SWLs"), the goal is to receive as many stations from as many countries as possible, also known as DXing. "DXers" routinely test the limits of their antenna systems, radios and radio propagationknowledge. Specialized interests of shortwave listeners may include listening for shortwave utility, or "ute", transmissions such as shipping, sailing, naval, aviation, or militarysignals, listening for intelligence signals ( numbers stations), or tuning in amateur radiostations.
Listeners often obtain
QSL cards from ham operators, 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 engineers.
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. There are also shortwave radio programs dedicated to shortwave listening and DXing, such as the
U.S.based "World of Radio" and "DXing With Cumbre", but recently these programs have been curtailed or dropped by many internationalbroadcasters. As of 2007, Radio Habana Cubastill hosts a program called DXers Unlimited.
While no one knows the exact number of SWLs, most estimates place the number in the millions. In 2002, according to the National Association Of Shortwave Broadcasters, for estimated numbers of households with at least one shortwave set in working order, Asia led with a large majority, followed by Europe, Sub Saharan Africa, and the former Soviet Union, respectively. The total estimated number of households worldwide with at least one shortwave set in working order was said to be 600,000,000. [http://shortwave.org/news/news0210.htm NATIONAL ASSOCIATION OF SHORTWAVE BROADCASTERS, Inc. October 2002] SWLs range from teenagers to retired persons to
David Letterman, who has mentioned on several occasions how much he enjoys listening to shortwave, particularly broadcasts by the British Broadcasting Corporation(BBC).
The precursor of shortwave listening was long distance listening in the
medium waveband, where broadcasting first developed. Frank Conradof Westinghouse, who developed the first medium wave broadcast station, KDKA in Pittsburgh, also set up the first shortwave broadcasts, as early as 1921. In 1924, the General Electricand Crosley companies started shortwave transmissions.In the 1930s, shortwave broadcasters from the United Statesconsisted of several private stations. The idea was to use popular American radio programs to attract audiences overseas, and thus to bring advertising revenue. But foreign audiences were difficult to measure, and were not always relevant to U.S. advertisers. During this decade, new receivers appeared on the market as well as popular shortwave magazines and clubs. Shortwave stations often offered unique QSL cards for DXers.
Europe, shortwave broadcasts from Britain and the Netherlandsbegan in 1927, and U.S. shortwave listeners could hear the well-organized international broadcasting efforts from Germany, Italy, the Soviet Union, Britain, and many other countries. Various well-known shortwave broadcasters became established. The BBC began as the "BBC Empire Service" in 1932 as a shortwave service. [ [http://news.bbc.co.uk/1/hi/world/europe/4375652.stm Analysis: BBC's voice in Europe] Jan Repa, BBC News Online: 25 October 2005] Its broadcasts were aimed principally at English speakers. Radio Moscowwas broadcasting on shortwave in English, French, German, Italian and Arabic by 1939. The Voice of America(or VOA) began broadcasting in 1942 as a result of the United States entry into World War Twoand was introduced with the Yankee Doodletheme that is still familiar to shortwave listeners.
Shortwave listening remained as an organized hobby during the second world war, although in a reduced form, with so many DXers in the military service or working late hours in defense industries. Most shortwave receiver manufacturers shifted to the war effort, but
Zenithbegan its popular multiband Trans-Oceanicseries in 1942. In some other countries, during the war, listening to foreign stations was a criminal offense. [http://www181.pair.com/otsw/review-elliott.html "On the Short Waves, 1923 to 1945" by Jerome Berg]
In the 1950s and 60s, shortwave DX columns in US magazines such as
Popular Electronics"Tuning the Short Wave Bands" and Electronics Illustrated"The Listener" became news sources for serious radio listeners. Electronics Illustrated "WPE Monitor Registration" program begun in 1959 even offered "callsigns" to hobbyists. A number of specialty radio clubs such as the "Newark News Radio Club" also arose during these decades and provided hobbyists with an exchange of DX news and information. In the 1970s, Popular Electronics and similar magazines expanded coverage of other areas of electronics lead to the cancellation of several longtime shortwave listening columns. [http://www181.pair.com/otsw/WPE.html "On The Shortwaves"]
Shortwave radio receivers
Serious hobbyists may use expensive
communications receivers and outdoor antennas. Typically, a modern solid state communications receiver will be of the superheterodyne type in double, triple or, more rarely, quad conversion. It will feature multiple RF and IF amplification stages and may have at least one IF stage that is crystal controlled. It will usually have an additional BFO product detectorfor SSB and CW reception capabilities. The frequency coverage of receivers of this type is typically in the range of 500 kHz to 30 MHz.
The front panel controls are typically more comprehensive than those on a local
broadcastreceiver. Usual features include: signal strength meter; RF gain control; AVC/AGC adjustments; antenna tuner; bandwidth filters; BFO tuning; audio limiters or attenuators. Frequency display dials may either be analog (typically marked to fine increments for accuracy) or digital.http://www.passband.com/pdf_files/HowToChoose.pdf "Passport To WorldBand Radio"] The older generation of vacuum tube-based communications receivers are affectionately known as boatanchors for their large size and weight. Such receivers include the Collins R-390 and R-390A, the RCAAR-88, the RacalRA-17L and the Marconi Electra. However, even modern solid-state receivers can be very large and heavy, such as the PlesseyPR2250, the Redifon R551 or the Rohde & SchwarzEK070. [Osterman, Fred (1998). "Shortwave Receivers Past & Present: Communications Receivers 1942-1997". Universal Radio Research, Reynoldsburg (USA). ]
Modern medium quality shortwave
radio receivers tend to be relatively inexpensive and easily accessible. Many hobbyists use even 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. The standard shortwave receiving antenna is the dipole antennawhich can be readily purchased or made by hand from a roll of wire and a couple of insulators.
Radios for shortwave reception generally have higher performance than those intended for the local AM or
FMbroadcast band. Good reception of shortwave signals requires a radio with good sensitivity, selectivity, and stability.
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. For voice communication, a bandwidth of as little as 2400 Hz could be adequate for intelligible 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.
PC controlled shortwave radio 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. 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 1980s and early 1990s came equipped with a control serial port. 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
firmwarecan be downloaded from the manufacturer's web site and uploaded into the flash memoryof 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 [http://www.ilgradio.com ILGRadio] . As of late 2006 they suspended the public broadcast database project and it is uncertain if they are going to resume it. As of 2008, the ILG database format is being updated as an open-source project called [http://ioc.com/radio lOCHAM]
Some control software designers have even integrated [http://earth.google.com/ 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 are able to see the transmitting antennas where the signal is originating from.
Shortwave radio control software
The field of software control of PC radios 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:
* a band table which has a row corresponding to each slice of the shortwave broadcast spectrum. A click on the row sets up the GUI for the minimum and maximum frequencies for that band. A modulation mode is sent to the radio which is appropriate for that band (usually AM mode), when the row is clicked by the user.
* a series of GUI controls corresponding to traditional radio controls such as frequency display, volume, mode, tuning rate and bandwidth. Usually included are a number of GUI slider controls. Moving the slider will tune the radio to a specific frequency and adjust the GUI frequency accordingly.
* a local time clock and a
UTCclock. By agreement all international shortwave broadcast schedules are constructed using UTC for standardization purposes.
* a signal strength meter which returns a value from the radio and displays it on the GUI. This is useful for seeing the relative signal strength of the received signal.
* some type of shortwave database, with the most widely used being the ILG database. The more advanced programs incorporate an interface to the ILG shortwave database. One control program displays a table that updates every minute that shows what stations are "on the air" in UTC time. This table can be pre-filtered by the user for languages. Simply clicking on a row of the table with a mouse tunes the radio to that frequency. In shortwave listening a frequency is sometimes referred to as a "channel". The shortwave bands are "channelized" at 5 kHz spacing.
* a frequency database lookup capability. When tuning across a shortwave band it is extremely helpful to be able to ID a station quickly, especially if a foreign language is being spoken. Some programs display a list of frequencies in a table as the user tunes in real-time.
* a scanning capability. This feature allows the user to tell the radio to start scanning from the beginning of the band to the other. As each frequency is tuned by the radio, the control program returns a signal strength to the control program and plots it. Once a scan of the band has been completed, the user can instantly see the state of the band in terms of which signals are strong and which signals are weak on any given frequency. By clicking on the plot display with a the mouse, the radio can be instantly tuned to that frequency. Using
modulo arithmeticthe programmer can guarantee that a mouse click always falls within the boundaries of a shortwave channel which is 5 kHz wide.
* integration of scanning with the ILG and [http://www.hfcc.org HFCC] databases simultaneously. Designers have taken the next step in integration and merged scanning with databases. By "mousing over" a scan, a GUI "tool-tip" is displayed that shows information from the database as to what station is currently using that frequency.
* text-to-speech interface. This feature can be optionally linked to frequency and mode changes or even database entries, to provide audio feedback to the user when certain fuinctions of the GUI are accessed.
* an integrated Conference Server, which allows real-time real-time coordination of listening frequencies over the Internet. This allows users connected over the Internet, for example, to "remote-follow" the tuning of other radios automatically. Typically included is a "chat" facility which allows users to text the group as new listening frequencies arise.
Perhaps the most widely used pure PC shortwave radio (manufactured continuously since 1998) is the American made [http://www.radio.tentec.com/Amateur/Receivers/TT320 RX-320D DSP receiver] . The "D" nomenclature is due to a design modification of the receiver, made by Ten-Tec circa 2004 that "taps" the 12 kHz IF output. This allows for the decoding of pure digital "pass through" signals such as DRM or Digital Radio Mondiale, as discussed elsewhere in this article. Otherwise the RX-320 and RX-320D receivers are identical in terms of their control and features.
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
demodulationcapability 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 Radiois dedicated to evolving a high-performance SDR. All the source code for this SDR is freely downloadable and modifiable by anyone.
Future of shortwave listening
Internetcaused 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 Europe, North America, Australasia, and the Caribbeangenerating many protests and creating many activist groups such as the Coalition to [http://www.savebbc.org/ Save the BBC World Service] .
Most of the prominent broadcasters are scaling back their analog shortwave transmissions or completely terminating them, but especially in
Africashortwave is still very common and active. Many expatriatesall 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 Mondialeis 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. [http://www.drm.org/ "Digital Radio Mondiale"]
Digital Radio Mondiale (DRM)
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 [http://drm.sourceforge.net/ 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.
Shortwave listening outside English-speaking countries
Since Korea has been divided into two states, shortwave listening in South Korea has never had a chance to activate itself due to political sensitiveness. [South Korean officials worried that shortwave could be used as a good method of receiving North Korean broadcasts by certain people.] Shortwave or shortwave receivers were the symbol of North Korean spies or pro-North Korean activists because there were some incidents that proved this prejudice [ [http://imnews.imbc.com//20dbnews/history/1996/2001989_3836.html MBC뉴스 - iMnews.com ] ] , and there were some cases in which the South Korean government confiscated shortwave receivers. [ [http://imnews.imbc.com//20dbnews/history/1994/1932516_3834.html MBC뉴스 - iMnews.com ] ] Until the liberalisation, it used to be a criminal offence for people without a ham radio operator's licence to possess a shortwave radio or listen to shortwave broadcasts. [http://www.crmo.go.kr/uploaddata/kukje/2004/kukje_01.pdf] In 1993, the South Korean government allows selling of shortwave (receivers) into domestic market. [ [http://srchdb1.chosun.com/pdf/i_service/read_body.jsp?ID=9303192302 조선닷컴! 1등 인터넷뉴스 ] ]
The 1973 oil crisis brought the root of 'enthusiastic' shortwave listening to Japan. Due to the oil crisis, many Japanese broadcasters had to cease midnight programmes, therefore, a lot of listeners there began to seek shortwave listening as an alternative. During the 1970s and the 1980s, a large number of Japanese people, especially teenage students, were excited about shortwave, and electronics companies like
Sonywere interested in manufacturing several shortwave receivers. Some shortwave listeners would gather QSL cards from various broadcasters all over the world. After the 1980s, enthusiasm for shortwave listening in Japan began to go down. These days, most of the Japanese listeners are composed of certain adults who are specially interested in shortwave listening. Some of them are nostalgic of that period.
In Third World countries, where their domestic MW/FM transmission networks are not developed as much as advanced countries (North America, Western Europe, Japan and certain East Asian countries), shortwave is used as a means for delivering domestic radio broadcasts. In China, for example, several domestic radio channels are retransmitted onto shortwave. Many listeners in this region find shortwave as a method to hear domestic services.
MW DX- Similar to SW DXing except on the MW (AM Radio) band
List of American shortwave broadcasters
* World Radio TV Handbook WRTH, ISBN 3-87463-356-X.
* Passport to World Band Radio, www.passband.com, ISBN 0-914941-61-5 (2007 ed.) ISBN 978-0-914941-66-8 (2008 ed.)
* [http://www.swling.com SWLing.com] ¨SWLing.com¨ - A step-by-step beginner's guide to shortwave radio listening.
* [http://www.primetimeshortwave.com/ Prime Time Shortwave]
* [http://www.passband.com/ Passport to World Band Radio]
* [http://www.strongsignals.net/ StrongSignals.net] Shortwave receiver reviews
* [http://www.drm.org/ Digital Radio Mondiale] - Digital HF Shortwave Standard
* [http://shortwave.hfradio.org/ Shortwave Listening at HFRadio.org] Search database of International Shortwave Broadcasters by frequency
* [http://propagation.hfradio.org/ Space Weather and Radio Propagation Center] View live and historical data and images of
space weatherand radio propagation.
* [http://swlfest.com/ Winter SWL Festival] Informational website for an annual gathering of shortwave enthusiasts in the USA
* [http://qrg.dk1ny.ath.cx/ Global Frequency Database]
The following external link is designed for use by
cell phonesand mobile devicesthat can display content using Wireless Markup Languageand the Wireless Application Protocol:
* [http://wap.hfradio.org/ WAP/WML SWL Resources] Search database of International Shortwave Broadcasting Stations by frequency, view
Space weatherand radio propagation data and images, and more.
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