Shortwave relay stations are transmitter sites used by international broadcasters to extend their coverage to areas that cannot be reached easily from their home state, for example the BBC operates an extensive net of relay stations.

These days the programs are fed to the relay sites by satellite, cable/optical fiber or the Internet. Frequencies, transmitter power and antennas depend on the desired coverage. Some regional relays even operate in the medium wave or FM bands.

Relay stations are also important to reach listeners in countries that practice Radio jamming

Radio jamming

Radio jamming is the transmission of radio signals that disrupt communications by decreasing the signal to noise ratio. Unintentional jamming occurs when an operator transmits on a busy frequency without first checking whether it is in use, or without being able to hear stations using the frequency...

. Depending on the effect of the Shortwave

Shortwave

Shortwave radio refers to the upper MF and all of the HF portion of the radio spectrum, between 1,800–30,000 kHz. Shortwave radio received its name because the wavelengths in this band are shorter than 200 m which marked the original upper limit of the medium frequency band first used...

 dead zone the target countries can jam the programs only locally, e.g. for bigger cities. For this purpose Radio Free Europe

Radio Free Europe

Radio Free Europe/Radio Liberty is a broadcaster funded by the U.S. Congress that provides news, information, and analysis to countries in Eastern Europe, Central Asia, and the Middle East "where the free flow of information is either banned by government authorities or not fully developed"...

/Radio Liberty with studios in Munich/Germany operated a relay station in Portugal, in the extreme west of Europe, to reach the then communist Eastern Europe.

Variations in design

One and only one broadcasting technology couples all of the components of a traditional shortwave relay station into one unit: the ALLISS

ALLISS

ALLISS is a fully rotatable antenna system for high power shortwave radio broadcasting in the 6 MHz to 26 MHz range. An ALLISS module is a self contained shortwave relay station that is used for international broadcasting.- FAQ :...

 module. For persons totally unfamiliar with the concepts of how shortwave relay stations operate this design may be the most understandable.

The ALLISS module is a fully rotatable antenna

Antenna (radio)

An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...

 system for high power (typically 500 kW only) shortwave radio broadcasting

Broadcasting

Broadcasting is the distribution of audio and video content to a dispersed audience via any audio visual medium. Receiving parties may include the general public or a relatively large subset of thereof...

 -- it essentially is a self contained shortwave relay station.

Most of the world's shortwave relay stations do not use this technology, due to its cost (15m EUR per ALLISS module: Transmitter + Antenna + Automation equipment).

Planning and design

A traditional shortwave relay station—depending on how many transmitters and antennas that it will have—may take up to two years to plan. After planning is completed, it may take up to five years to construct the relay station.

The historically long design and planning cycle for shortwave relay stations ended in the 1990s. Many advanced software planning tools (not related to the relay station design proper) became available. Choosing a series of possible sites for a relay station is about 100 times faster using Google Earth

Google Earth

Google Earth is a virtual globe, map and geographical information program that was originally called EarthViewer 3D, and was created by Keyhole, Inc, a Central Intelligence Agency funded company acquired by Google in 2004 . It maps the Earth by the superimposition of images obtained from satellite...

, for example. With the modern graphical version of Ioncap, simplified propagation studies can completed in less than a week for any chosen site.

In some cases, existing relay stations can have their designs more or less duplicated, thus speeding up development time. However, there is one general exception to this: the ALLISS

ALLISS

ALLISS is a fully rotatable antenna system for high power shortwave radio broadcasting in the 6 MHz to 26 MHz range. An ALLISS module is a self contained shortwave relay station that is used for international broadcasting.- FAQ :...

 Module. From initial planning to deployment of ALLISS Modules may take a mere 1.5 years to 9 months depending on the number of modules deployed at one time in a particular sector of a country.

Graphic examples

How relay stations operate

These are considered general operating parameters:

• 20 hours per day, but geopolitical reasons may dictate some stations run 24 hours per day (a 168 hour week)
• Generally 360 days per year, depending on the number of redundant transmitters and antennas
• Relay Stations generally consume from 250 kilowatts (kW) to 10 megawatts (MW)
• A single 100 kW SW transmitter consumes 225 kW RMS as a general rule
• A single 300 kW SW transmitter consumes 625 kW RMS as a general rule
• Modulator efficiency: Class-B modulators have about a 65% efficiency level, but digital (PDM or PSM or hybrid variants) modulators have about a 85% efficiency level as a general rule (for Amplitude Modulation)
• Broadcast times and frequencies are under ITU
  Itu
  Itu is an old and historic municipality in the state of São Paulo in Brazil. The population in 2009 was 157,384 and the area is 641.68 km². The elevation is 583 m. This place name comes from the Tupi language, meaning big waterfall. Itu is linked with the highway numbered the SP-75 and are flowed...
  
   regulation

How relay stations are designed

General requirements of shortwave relay stations:

• Road access (fairly universal)
• HVAC mains access building or transformer in the transmitter building itself
• Staff quarters (if the relay station is not fully automated)
• Incoming audio processing centre, but since the mid 1980s this has evolved into one to five rack units
• Transmitter hall (50 kW, 100 kW, 250 kW, 300 kW, 500 kW shortwave
  Shortwave
  Shortwave radio refers to the upper MF and all of the HF portion of the radio spectrum, between 1,800–30,000 kHz. Shortwave radio received its name because the wavelengths in this band are shorter than 200 m which marked the original upper limit of the medium frequency band first used...
  
   transmitter)
• Switch matrix (but these are not typically used by ALLISS
  ALLISS
  ALLISS is a fully rotatable antenna system for high power shortwave radio broadcasting in the 6 MHz to 26 MHz range. An ALLISS module is a self contained shortwave relay station that is used for international broadcasting.- FAQ :...
  
   modules)
• Balun
  Balun
  A balun is a type of electrical transformer that can convert electrical signals that are balanced about ground to signals that are unbalanced , and the reverse. They are also often used to connect lines of differing impedance...
  
  s (but their use is not always required nor universal)
• antenna tuner
  Antenna tuner
  An antenna tuner, transmatch or antenna tuning unit is a device connected between a radio transmitter or receiver and its antenna to improve the efficiency of the power transfer between them by matching the impedance of the equipment to the antenna...
  
  s (sometimes called ATUs or roller coasters because of their appearance)
• Feeder lines (coax cable and open feeder lines are the most common feeders in use)
• HRS-type antennas, or occasionally log-periodic (horizontal)
• In parts of the developing world log-periodic (horizontal) antennas are used to provide less directional gain to a target area.

Where the broadcast programs go

• generally to target areas that are more than 300 km from the transmitter site
• most shortwave relay station target areas are 1500 km to 3500 km from the transmitter site

Historical innovations

In the IEEE Book series "The History of International Broadcasting" (Volume I) it is pointed out that the German propaganda ministry had mobile shortwave relay stations during WWII. These mobile relay stations consisted of a generator truck, transmitter truck and an antenna truck.

• It is assumed that these mobile relay stations were in use from about 1940 onwards.
• It is assumed that the antennas used where Rhombic, but could have been Log Periodic.
• It is assumed that the transmitter power was 50 kW, and that these transmitters required a full size truck.
• It is assumed that the relay stations were moved every two or three days, to prevent HFDF.
• It is assumed that no stations were ever destroyed via aircraft, but that many would have been captured during 1945 by both the US, British and Russian forces.

Technical notes:

• In order for the relay network to get its audio feeds, the PTT constructed concrete bunker telephonic termination points throughout the German state.
• Only RIZ (Radio Industry Zagreb) produces mobile shortwave transmitters in the current post-Cold War era. RIZ's designs are clearly not inspired by the German wartime innovation, as they are based around standard shipping containers.
• RIZ's portable designs are meant to be portable temporary replacement transmitters, not truly mobile shortwave relay stations.
• The only kinds of antennas that are both mobile and directive and also suitable for this kind of relay station design are the Rhombic and Log Periodic antenna types.

Notable sites : Issoudun

The International broadcasting center of TDF (Télédiffusion de France) is at Issoudun/Ste Aoustrille. As of 2011, Issoudun is utilized by TDF

TDF

TDF may refer to:Technology:* TenDRA Distribution Format, a design of abstract machine* Testis determining factor, gene that results in maleness* Tenofovir disoproxil fumarate, the antiretroviral drug...

 for shortwave

Shortwave

Shortwave radio refers to the upper MF and all of the HF portion of the radio spectrum, between 1,800–30,000 kHz. Shortwave radio received its name because the wavelengths in this band are shorter than 200 m which marked the original upper limit of the medium frequency band first used...

 transmissions. The site uses 12 rotary ALLISS

ALLISS

ALLISS is a fully rotatable antenna system for high power shortwave radio broadcasting in the 6 MHz to 26 MHz range. An ALLISS module is a self contained shortwave relay station that is used for international broadcasting.- FAQ :...

 antennas fed by 12 transmitters of 500 kW each to transmit shortwave broadcasts by Radio France International (RFI), along with other broadcast services.