Relay station

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Simple relay point to increase the range

A relay station (also relays radio station or short relay ) made possible by automatic reception and retransmission of radio signals , a data transmission over greater distances than would be possible with a direct connection. When it comes to satellite communication , one speaks of transponders . So-called repeaters are used in wired technology .


The term itself is of French origin ( relais = passing on). It referred to a chain of optical telegraphy stations that were in visual contact with one another. A mast with two signal arms stood on the roof of these stations. Each position of these arms means a letter. The arms could be operated from inside the station. Urgent dispatches could be transmitted very quickly.


An amateur radio relay station for APRS and IRLP in the 70 centimeter band
Cup circle filter of a relay station

A relay in radio technology is a remote-controlled radio station, usually at an exposed location, which, by converting and amplifying the signals from an input frequency (reception frequency ) to an output frequency (transmission frequency), connects fixed, portable or mobile radio stations in different services, often Telephony ( radiotelephone ) enabled. The distance between the input and output frequencies is called the shelf.

turn on

Permanent broadcasting is usually not permitted or makes no economic sense. The relay station must therefore first be switched on before use. This is effected differently with the different radio services:

  • In amateur radio service , a ringing tone is (1750 Hz) traditionally used. After receiving this start signal, the relay station remains open for a few seconds longer than it receives a signal. In the case of individual relay stations, sending an unmodulated carrier is sufficient. With these methods, however, the relay can also be kept on transmission by interference signals and thus blocked for users. Other relay stations are controlled via CTCSS . This method prevents touching and holding due to interfering signals and is therefore particularly advantageous for exposed locations.
  • In the BOS radio there are different ringing circuits (call-1, call-2 each short or long) and also carrier-controlled relays. A heavily used emergency channel will usually be carrier-controlled, whereas a seldom used disaster control channel will be activated with a tone call.
  • In corporate radio, it is not desired that external companies speak via their own relay. The authorized user therefore sends out a 5-tone sequence or a CTCSS to use the relay.
  • In trunked radio , the organization channel sender runs continuously to indicate availability to the user and to allow them to log into this station. In the event of a request to speak, the parties involved are switched from the organization channel to a traffic channel. A total of four channels are usually available at one location. In addition to the organization channel, there are still three traffic channels. The traffic channels are only switched on when used. If all traffic channels are already in use, the calling station receives a busy signal.


After switching on, the relay station transmits as long as it is spoken. To indicate that the previous speaker has spoken, some relay stations send a roger beep. In order to prevent the users from cracking the squelch, the relay station continues to transmit an unmodulated carrier for a few seconds (lag). If, for example, no speech is made in this delay time of 10 seconds, the transmitter of the relay station switches off. However, the relay station remains active for some time (for example 60 seconds) and the calls can be continued.

In the BOS radio relay stations are partially connected in series, e.g. B. a paramedic or police officer working via the local relay station switches to a 4 m / 2 m crossband (also RS2 or large) relay station when leaving the vehicle in order to remain within walking distance. In these cases, the delay time described above can be a hindrance. In such a radio network you would work with an RS1 circuit. Details on BOS sequence controls can be found under BOS radio # tape positions .

Turn off

  • If the delay times are not used, the relay station switches off.
  • A speaking time limit, so-called “offside trap” or “chatter block”, is installed in some stations to prevent continuous broadcasts. After a maximum transmission time of five minutes, for example, the relay switches off.
  • In trunked radio networks and some private mobile networks, the microphone has a contact in its suspension. This is switched when the microphone is hung up and signals the end of the call to the relay station.
  • In amateur radio, there is a requirement that the responsible operator must be able to switch off his relay at any time in the event of improper use. For this purpose, an extra receiver is usually mounted on the relay station. A corresponding ringing tone on this secret channel then switches off the relay station.
  • A telecontrol receiver was installed in relay stations for agriculture and forestry in the GDR . The corresponding transmitter was in the district leadership of the SED . Should the farmers abuse the relay station, for example to call for a demonstration, to break the border together, etc., the party leadership would have had the opportunity to switch it off.

Radio networks

Simultaneous wave relays are called relay stations that are connected to a base station via a link, from which the information received from the relay station is again distributed to other relay stations via link links and these relay the information again via the output frequency. This ensures that the individual relay stations do not cover an area that is too large, so that a second radio communication circuit a short distance from the first can transmit on the same frequency (wave) without the two radio communication circuits interfering with each other.

In radio technology, the term relay station has become established for the transmission of radio waves . Radio waves are attenuated to different degrees during their transmission by the various media such as water or air . A relay station is therefore necessary to increase the range. This is done by amplifying and, if necessary, correcting the original signal, which is then passed on.

Relays are often used in the amateur radio service , but also in the non-public mobile land radio service and in the radio service ( filler transmitter , television converter ). Relays of the non-public mobile land radio service work in the corresponding assigned frequency ranges, i.e. in the VHF range.

Relay in broadcasting

In broadcasting , a relay station is a transmission system that broadcasts the program of a radio station at a location far away from the home station. The purpose of such systems is to achieve improved reception quality in the target area through the additional transmission of the radio signal.

Shortwave transmitters operated by international broadcasters are a frequent application . However, vehicles are also used as relay stations. For example, television broadcasts, for example of sports or major events, are often transmitted to an aircraft flying over the action , from which the signals are forwarded to the transmission center.

Examples of international radio stations that use relay stations are BBC World Service , Voice of America (the system is operated by IBB ), Deutsche Welle , Radio France Internationale , Radio Exterior de España and Radio Nederland Wereldomroep .

The radio program is the home country of the international broadcaster mostly via satellite or SSB - modulation via ball receiving transmitted to the relay station.

Large relay stations are located, for example, in Ascension , Antigua , Bonaire , Kigali / Rwanda, Botswana , Trincomalee and Iranawila in Sri Lanka, Tangier / Morocco, Kranji / Singapore, Sines / Portugal and Udon Thani / Thailand.

Relay in the amateur radio service

Commercial relay station for amateur radio in the 2-meter or 70-centimeter band, from the amateur radio manufacturer Yaesu / Vertex
Amateur radio relay station DM0TMH for the 70 centimeter band with individual components of commercial devices

In the amateur radio service, relays operate in frequency bands from 10 m to over 3 cm and in practically all operating modes . FM relays in the 2-meter and 70-centimeter band are often used to amplify mobile stations and are the most common in amateur radio.

Amateur radio relays are often in exposed locations (such as on the Brocken and Zugspitze , but also on high-rise buildings in cities or telecommunications towers ) in order to achieve the greatest possible range. Each relay station must be licensed with the Federal Network Agency . The location and the frequencies of the relay stations are recorded in the license of the Federal Network Agency. In Germany , the call sign assigned by the licensing of a relay radio station usually begins with DA5, DB0, DF0, DM0 or DO0.

In Austria, the relays have a club station call sign and always begin with an X. Example: 70 cm relay Steyr / OÖ OE5XHO.

The person responsible for the relay is responsible for the relay station and usually looks after the station with a high level of volunteer work. The power supply of some amateur radio relays is buffered by means of a UPS or works independently with solar power , so that they are still available for emergency radio purposes even in the event of a power failure .

Amateur radio relays can be connected to one another with directional radio or via the Internet (see Echolink ) to increase the range .

Some amateur radio relays are also broadcast live on the Internet as an audio stream .

Another variant of amateur radio relays are satellite relays; these are often built into amateur radio satellites , but also as an additional application in commercial satellites.

Special relays for digital modes such as packet radio are called digipeaters . Both the digipeaters and the relay stations for voice are now connected to form networks. The amalgamation of several digipeaters is called a packet radio network.

Relay in analog company radio

Commercial relay station for professional radio in the VHF or UHF band

The use of relay points in corporate radio is restricted in Germany to certain users for their own internal company communication, such as authorities and organizations with security tasks (BOS), energy providers, water supply, sewage disposal. These companies, which are particularly important for supplying the population, are allowed to operate their own radio networks in the form of individual or networked relay stations. However, with the use of public networks such as GSM or trunked radio, this is declining among utility companies. The BOS will also take their respective repeaters out of operation after the Tetra has been set up in Germany.

Relay in digital corporate radio

Digital DMR relay station with two speech channels: Motorola MOTOTRBO DR3000

With the introduction of digital mobile radio in 2007, the corresponding radio regulation in Germany was also adapted to the dwindling number of users of commercial radio. From the 11/2008 edition, the Federal Network Agency allows the use of relay stations in the administrative regulations for frequency assignments in non-public mobile land radio for all authorized company radio users, not just the few users from analog company radio . In addition, there is now talk of "composite use", i. H. the installer of the relay station can now also let third parties use it. You can now become a telecommunications network operator with relatively little effort .

Known types of relay stations: BOS: Bosch-FSO, AEG-Teleregent, FuG-7, FuG8-c, FuG9-c

Commercial radio:

  • Bosch FSO
  • AEG Teleregent
  • Motorola MC-Compact, MTR2000, DR3000, MTR3000, Quantar, Quantro

Relay in cellular networks

Repeaters or relay stations are also used in the mobile communications sector in order to (better) supply areas. A repeater is characterized by the fact that it does not originally generate the emitted signal itself (in the sense of baseband modulation), but essentially receives, amplifies and forwards the signal from an external source ( base station and mobile phone ). As a rule, signals are only influenced by filtering in order to filter out interference or undesired adjacent channels (e.g. the competitor in the case of GSM). Modulation, frequency and phase are not directly influenced. Repeaters are mostly full duplex devices that transmit and receive at the same time. The two traffic directions uplink and downlink are selected using a duplex switch . This is only possible if the cellular network has different frequencies for uplink and downlink (for example with FDMA systems such as GSM).

A distinction can be made between broadband repeaters and channel-selective repeaters. The channel-selective repeater usually has more power than the broadband repeater. It must be able to amplify at least as many channels as the base station to which it is connected has. Broadband repeaters either amplify the entire band (for example GSM 900) or that part of the band that has been assigned to the network operator. One advantage of broadband repeaters is that if the channels at the base station are changed, the repeater does not have to be reprogrammed.

There are several usage scenarios:

  • Illumination of shaded areas such as valleys or gorges
  • Increase in the data rate through higher field strengths (for CDMA2000 or UMTS cellular networks)
  • Supply of special areas (such as ICE routes)
  • Supply of closed areas (such as subway, underground parking, mines, exhibition halls, commercial buildings, etc., but also within ICE wagons due to the high attenuation from the steamed windows and on ships)

The supply is active, i.e. H. The repeater / relay station contains amplifiers and other active elements such as monitoring and control computers, alarm systems, etc.

Two technologies are currently in use for cellular repeaters:

  • Cable or HF supplied and distributed : Here the source signal is picked up via one or more (connection) antennas , distributed via coaxial cables and emitted via one or more antennas or a beam cable . This is possible in systems in which the active elements (relay stations) are a maximum of approx. 1000 m apart (parameter: frequency-dependent cable attenuation).
Fiber optic tunnel repeater system for GSM
  • Optically supplied and distributed : In this case, too, the source signal is picked up by antennas, as in cable systems. Alternatively, one or more base stations (BTS) can be connected directly to an optical distribution system via the antenna connection of the BTS if the traffic to be expected in the cell phone calls for its own BTS (e.g. in exhibition halls). The long-range distribution does not take place via coaxial cable, as in the first case, but optically in a glass fiber . A laser is modulated with the RF signal and sends the laser radiation to a receiving point via single-mode glass fibers . This is where the laser light is converted back into HF ( demodulation ). The RF signal is filtered, amplified and emitted. With optical distribution systems, HF signals can be transmitted over a distance of up to 20 km (inexpensive) on the fiber optic cable due to the low attenuation. This is no longer possible with coaxial cables. Examples of installations are the tunnel supply for the new ICE routes , as well as the subway supply (for example: U-Bahn in Berlin ) and World Cup stadium supply (for example Allianz Arena ).

The first systems are now on the market that use the fiber optic link digitally, i.e. as a data connection. For this purpose, the signal is demodulated, digitized, transmitted over the fiber and a carrier is modulated again.

Web links

Commons : Amateur Radio Relay Stations  - Collection of pictures, videos and audio files

Individual evidence

  1. ^ Albert Schlaubitz: The CTCSS ringer, technical necessity, fad or even chicane . Relay community HB9F Bern.