Carrier frequency system

from Wikipedia, the free encyclopedia

A carrier frequency system ( TFA ) is a device for voice or data transmission over existing communication or power networks . Carrier frequency systems use carrier frequency technology, a method to make multiple use of existing transmission paths. The signals are additionally modulated onto the line via one or more carrier frequencies . The transmission via message and telephone networks is often known as carrier frequency technology and in power networks as PowerLAN or Powerline Communication (PLC) .

Due to the multiple use of existing lines, these transmission methods are considered to be very quick and inexpensive to implement and implement. Safety aspects and the resistance to interference are also of particular importance.

Carrier frequency systems can be differentiated according to the frequency range used, the type of modulation used and the area of ​​application.

Messaging for telephone and teletype channels

The frequency division multiplex method allows the multiple use of existing lines. Each speech channel is assigned its own carrier frequency, onto which the audio signal is modulated and selectively demodulated at the receiver. Many of these methods often worked with amplitude and later partly with frequency modulation.

The carrier frequency systems have been used as feeder systems for radio links and for transmission with coaxial cables instead of the long-distance cables that were initially used . The repeater offices took over the amplification of the carrier frequency signals and were in some cases also able to forward TF channels to other TF cable routes.

These methods, like alternating current telegraphy , were later replaced by digital transmission methods and fiber optic cables . In the past they were an important method (like phantom switching, for example ) for the multiple use of line systems.

Ripple control technology

The term ripple control (often referred to as TRA = T onfrequenz r undsteuer a nLocation abbreviated) the carrier frequency technology will require decades to mass control of devices that do not require feedback such. B. street lighting, load release ( night storage heating ) or tariff switching (night power). The technology was also used to alert emergency services. The Darmstadt professional fire brigade alerted its off-duty staff and the four volunteer fire brigades in the city area. This was also the first "silent" alert at the Pfungstadt fire brigade.

The network operators use different frequencies to avoid mutual interference. Frequencies in the low frequency range (up to about 2 kHz) are used, as signals with these frequencies are only subject to relatively low attenuation (the low-voltage network is predominantly inductive, the insulating materials used do not yet attenuate) and can therefore reach any end device. Because of their low frequency, these systems do not cause any interference with radio reception.

Transmission of messages via high voltage lines

TFH connection in a 110 kV switchgear

Carrier frequency systems in the frequency range between 30 kHz and 500 kHz are used for the exchange of messages between facilities of energy supply companies. Here, the term T räger f requency-message transmission over H ochspannungsleitungen (TFH) in use. As a rule, these signals are transmitted in single phase via a conductor of high or medium voltage overhead lines. In the immediate vicinity of the respective lines (up to a few 100 meters away from the line), they can sometimes considerably interfere with the reception of radio services operating in this frequency range, such as long-wave radio transmitters , the radio clock transmitter DCF77 or the navigation system LORAN-C for sea and aviation. For these reasons and because of the low maximum transmission bandwidth, carrier frequency systems are increasingly being shut down within energy supply companies and replaced by radio relay systems or cables (mostly fiber optic cables in the earth wire) for the purpose of transmitting messages .

The carrier frequency systems and carrier frequency signal relay stations were previously also used to provide the electricity companies with high-availability in-house telephone systems in automatic dialing. One spoke here of EW telephony .

Carrier frequency signals can travel considerable distances (several hundred kilometers) on power lines.

In order to prevent uncontrolled propagation, blocking reactors are sometimes found in the current loops of branching lines and in the switchgear of substations , which block these signals. With very long lines it is sometimes necessary to use repeater stations.

In the former Soviet Union, the earth cables are used on some lines for the transmission of carrier frequency signals, which are attached to the masts with insulators.

Household applications

Voice transmission

In the home, the so-called baby monitor is probably the best-known application of this technology. It works at frequencies around 100 kHz, i.e. below the long-wave broadcast range .

PowerLAN

Procedure Link rate Frequency range
Home plug 011 Mbit / s 04… 027 MHz
Homeplug Turbo 085 Mbit / s 02… 027 MHz
Panasonic AV 180 Mbit / s 03… 030 MHz
Homeplug AV 200 Mbit / s 02… 032 MHz
DS2 AV 200 Mbit / s 02… 030 MHz
Homeplug AV2 500 Mbit / s 02… 086 MHz
Mediaxtream 882 Mbit / s 50 ... 300 MHz

(Another variant of) TFA can be used to network computers within a Local Area Network (LAN). These specifications are available from Intellon ( Homeplug ), DS2 , Panasonic and Gigle ( Mediaxtream ). The advantages are that no cables have to be laid, parts of the building that cannot be reached by WLAN can be supplied and, compared to WLAN, the transmission quality is considerably more stable, which is particularly required for HD video streaming. "The disadvantage of Powerline technology compared to WLAN is that the manufacturers have not yet been able to agree on a uniform standard and the comparatively high price."

The International Telecommunication Union (ITU) is working on a standardized technology for the wired transmission of digital data in the home (home network). The G.hn standard should be able to use all lines laid in the house (power, telephone and network cables) at speeds of up to 1 Gbit / s. In October 2009, recommendation G.9960 for the physical layer and the architecture of the standard was passed by the ITU. Recommendation G.9961 for the data link layer followed on June 11, 2010. ABI Research forecast (2008) for 2013 that 42 million devices with support for the G.hn standard could be sold worldwide.

Some providers of household electronics offer remote control options for selected products via the home electricity network via Powerline. The devices can then be monitored or controlled via a connected PC or a type of remote control ("control panel").

The modems sold in the European Union are type-tested as part of the CE marking . The disturbance of others through radiation is within the legal requirements for the tested design.

Since power supply networks ( low-voltage networks ) for three-phase current transmission usually consist of three external conductors, the problem with message transmission is to distribute the high-frequency carrier frequency signals as evenly as possible over these three external conductors. For this purpose, so-called phase couplers are used in the low-voltage networks, which only connect the outer conductors to one another for the carrier frequency signal.

The Federal Network Agency recorded only two fault reports between spring 2005 and spring 2007 that were due to in-house powerlines. The resulting administrative offense proceedings came to an end with the payment of a fine.

Home automation

Various providers and protocols deal with consumers that are remotely controlled via the power grid and the comparatively slow data transmission within a house. One example is the X10 protocol . What they all have in common is the carrier-frequency transmission of the signals, the programmability of the various modules for input and consumer control as well as the short range, which only requires very little carrier power and can therefore be below the minimal limit of a radio license (5 mW). The X10 transmission works at only 120 kHz, which means that radio interference is very unlikely.

Internet access via powerline

With these carrier frequency systems (also known as powerline ), Internet access is provided via the power cable on the route between the socket at the end user and the transformer station of the energy supplier.

The transition to pure internet lines, the backbone, is in the transformer station. Since different frequencies are used on the route between the transformer station and house connection and on the route between house connection and socket, a total of three adapters are required: One in the transformer station, one at the house connection at the electricity meter and one at the socket. The house connection must not be more than 300 m from the transformer station and no more than 100 m from the socket; higher ranges are only possible with amplifiers.

The frequency range used is 1 to over 30 MHz , with between 1.5 Mbit / s and 205 Mbit / s possible per transformer station. This bandwidth is available to all active users of the service who are connected to a transformer station.

The regulatory authority for telecommunications and post stated in its activity report 2002/2003 that the manufacturers and operators of these so-called powerline carrier frequency systems (carrier-frequency data transmission via the power grid to the Internet connection) have now ceased their activities in Germany with a few exceptions, and mentions them in this In connection with the unauthorized high radio emissions (interference field strengths), which cause problems in terms of electromagnetic compatibility . In the meantime, these carrier frequency systems are viewed increasingly critically, since the enormous radiation of high frequency makes conventional communication via shortwave practically impossible. For this reason there were massive protests by radio amateurs . Novel powerline modems can detect the existence of shortwave broadcast services at the location and at the time of their operation by observing the background noise. The frequencies occupied by the radio are then left out of the powerline communication. However, this technology usually only works with transmitters that transmit continuously, as the modems usually only set the frequencies after switching on or at longer intervals.

Dissemination of radio programs

For the distribution of amplitude-modulated radio programs , power lines and telephone cables were previously used in the long-wave range . In Germany this technology was introduced in 1939 as wire radio , in Switzerland it was called telephone broadcast and in Norway it was called Linjesender . This system was very common in Russia because it only allowed reception from Russian channels. This technology is still used today in some countries for local broadcasting.

There are systems that use existing telephone lines and systems for power lines. In the head-end stations, the TF signals were coupled to the lines via special transformers and capacitors.

In the case of carrier frequency technology, the existing line system with the coupling units serves as a distribution medium, while in the case of so-called light antennas , the connected power line should act as an antenna .

Emissions and unwanted emissions from carrier frequency systems

Current-carrying conductors act like antennas and radiate the signals from carrier frequency systems into the environment.

Since a power line without shielding also picks up signals from the environment and from connected devices, the problem is that high transmission levels of the TFA modems are necessary to maintain a good connection. However, high transmission levels of the modems lead to higher signals emitted.

With sensitive receivers using directional antennas, TFA signals can still be received a few dozen, sometimes even a few 100 meters away from the line.

In the shortwave range , there is interference in shortwave reception, especially in areas where power lines are laid above ground. This interference affects, among other things, the radio of the police , security authorities , taxi or amateur radio , shortwave radio , the maritime radio service , weather radio, aviation radio , military radio services, embassy radio , press agencies as well as the shortwave radio networks of the UN and ICRC . A notch filter can be used to keep sensitive shortwave applications free from interference from the TFA signal. However, this is only a workaround, as there are no areas other than the ISM areas in which interference is “allowed”. You can only avoid the most likely conflicts, the problem itself remains and each masked frequency range reduces the bandwidth of the transmission within the carrier frequency system.

From the NATO there is a report thereon (RTO TECHNICAL REPORT TR-IS-050) on the expected radio interference caused by data transmission over unshielded power lines.

In Austria , the Federal Ministry for Transport, Innovation and Technology (BMVIT) has collected fault reports for the powerline network operator in Linz and listed measurement results. The frequencies from 3 to 20 MHz are affected, there are malfunction reports for amateur radio and emergency radio . The decision of the BMVIT to the operator not to cause any radio interference in other telecommunication systems was canceled by the administrative court because no specific ( enforceable ) measures were ordered and the connection between the radio interference and the powerline network could not be proven. At the same time, however, he decided that the ministry may order such measures even without specific disruptions if the network does not meet the requirements of EC Directive 89/336 / EEC, which in particular requires the recognized rules of technology.

In Germany there are maximum values ​​for TFA interference radiation, which are specified in the usage regulation 30 (NB30) of the frequency range allocation plan. The Administrative Court of Baden-Württemberg considers it to be inapplicable as it has not been notified to the European Commission . Therefore, the Federal Network Agency cannot order TFA restrictions when the NB30 values ​​are exceeded, but only in the event of specific disruptions. The background to this are complaints from a radio amateur who suffered interference, whereupon the Federal Network Agency issued an immediately enforceable order against the TFA operator in Mannheim , according to which the NB30 values ​​may no longer be exceeded.

In the operating instructions of the TFA devices you will usually find a note similar to the following: This device X can cause radio interference in living areas; in this case, the operator can be required to take appropriate measures. In order to protect yourself as an end user, there are forms that you should have the seller sign in order to be reimbursed for the costs of the "reasonable measures" described above in the event of interference.

See also

literature

  • Frank Reinhardt: POWERLINE. Constitutional, administrative and telecommunications problems. Peter Lang-Verlag, 1st edition 2003. ISBN 3-631-51180-9 .

Web links

Emissions

Individual evidence

  1. ↑ Jochen Fritz: Frequencies. In: Basics of ripple control technology. Retrieved January 28, 2018 (German).
  2. ^ AEG auxiliary book for electrical light and power systems , Essen 1953
  3. ↑ Lothar Schnitzler: Victory of the socket . In: Wirtschaftswoche . No. 34, 2008, ISSN  0042-8582 , page 108 ( [1] ).
  4. ↑ Sheila Lashford: United Nations ITU-T's G.hn Approved as Global Standard for Wired Home Networking. (No longer available online.) In: HomeGrid - Press Releases and News. HomeGrid Forum, June 11, 2010, archived from the original on September 11, 2010 ; accessed on June 17, 2011 (English). Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.homegridforum.org
  5. ↑ pressinfo: Press release: New global standard for fully networked home. International Telecommunication Union (ITU), December 12, 2008, accessed on January 28, 2018 .
  6. ↑ c't special networks . 01, 2008, page 19.
  7. ↑ Manfred Breul from the industry association BITKOM , quoted from: Verena Wolff: Data streams from the socket ( Memento from September 27, 2007 in the Internet Archive ) . In: Aachener Zeitung . July 2, 2007.
  8. ↑ Assessment of NATO ( memento of the original from October 25, 2007 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. on the subject of radiation from PLCs from unshielded cables (PDF, English; 9.7 MB) @1@ 2Template: Webachiv / IABot / ftp.rta.nato.int
  9. ↑ VwGH knowledge GZ. 2005/03/0245 of June 8, 2006. RIS - Legal Statements and Decision Text, July 17, 2007, updated October 7, 2008. Last accessed November 12, 2015.
  10. ↑ PLC may continue to be operated in Mannheim , final resolution 1 S 787/05 of February 7, 2006 (PDF; 67 kB)
  11. ↑ Form (PDF; 23 kB)