Longitudinal wave

As long waves ( English very low frequency , short- VLF ) refers to electromagnetic waves in the frequency range of 3 to 30k Hz - (Not to be confused with low frequency (<3 kHz) (see frequency band )).

The frequency range below 9 kHz is not subject to any regulation by the international telecommunications organization (ITU).

history

In the early days of radio technology, telephony with the help of amplitude or single sideband modulation was repeatedly tried in the range from 20 kHz , but the result was unsatisfactory due to the low transmission bandwidth. The historic long-wave transmitter SAQ in Grimeton (near Varberg in Sweden ) is in operation for around half an hour on special occasions and can even be viewed in action at these times, such as on Alexanderson Day.

application

VLF receiving antenna, magnetic antenna in the form of a ring in the center of the picture, on a submarine

VLF signal at 18.1 kHz

Long waves are almost only used for the transmission of commands to submerged submarines because of the low possible bandwidth of a few Hertz in this area , since radio waves in this frequency band can penetrate about 10 to 30 meters into the sea water. During the Second World War , the German Navy operated the Goliath transmitter near Kalbe an der Milde on 16.55 kHz (main frequency) from 1943 to 1945 . The German Navy has been using the Rhauderfehn marine radio station ( call sign DHO38) since 1982 . At a transmission frequency of 15 kHz, the penetration depth in sea water is about 20 meters. At 82 Hz (still below the longest wave, then called SLF ) it is about 300 meters. The Russian transmitter ZEVS uses 82 Hz; the American transmitter Sanguine used 76 Hz for submarine communication.

The limits of the depth of penetration are fluid with the skin effect , as the depth of penetration also depends on the transmission power, the size of the receiving antenna, the sensitivity of the receiver and the properties of the sea water (salinity, temperature).

Another area of application is mine radio . Here the antenna wires are laid in the shaft, so the distance to the receivers is never particularly large.

They are also used for radio navigation ( alpha ) and for transmitting time signals ( beta ).

A rather "exotic" application can be found in the investigation of the reflection behavior in the upper layers of the earth using the VLF method in geophysics . In this way, large geological structures in the order of magnitude of the wavelength can be found if they differ from their surroundings by their electrical conductivity.

Antenna system

2.2 km long Alexanderson transmitting antenna for 17.2 kHz of the longest wave transmitter Grimeton

Long-wave transmitters require large antenna systems, which consist of several masts over 100 m high, and take up an area of several square kilometers. In contrast to other large-scale technical systems such as airports, however, nature is only negligibly affected in the area of a long-wave transmitter. There are also mobile long-wave transmitters on airplanes such as the Boeing E-6 as part of TACAMO , where a wire up to 7 km long is dragged along as a transmitting antenna from the aircraft.

Wave propagation

Longitudinal waves propagate in the waveguide between the earth's surface and the ionospheric D-layer in an altitude range between about 70 km and 90 km ( ionospheric waveguide ). One exception is the Whistler spread. Since their wavelengths (10 km to 100 km) already have the dimensions of the waveguide, their propagation can only be described to a limited extent by the radiation optics (interference between ground waves and waves reflected once or twice at the ionosphere). This is only possible for relatively short distances between the transmitter and receiver; z. B. at a frequency of 15 kHz to about 1000 km. For larger distances, a wave-optical approach is necessary. Finally, in the low frequency range (frequency less than 3 kHz), only the wave-optical solution is possible. The Schumann resonances are an extreme case . These are the natural vibrations in the cavity between the earth's surface and the ionosphere with a wavelength the size of the earth's circumference and a frequency of approx. 7.5 Hz as well as harmonics.

List of longest wave transmitters

The following list contains all long-wave transmitters that can be received in Germany with commercially available PC sound cards (which have a maximum sampling rate of 48 kHz). Transmitters with frequencies above 24 kHz are not taken into account.

Callsign	frequency	Location	Remarks
-	76 Hz	Clam Lake (Wisconsin), Escanaba River State Forest (Michigan)	Sanguine
-	82 Hz	Kola - peninsula (Russia)	ZEVS
-	11.905 kHz	Russia (various locations)	Alpha navigation
-	12.649 kHz	Russia (various locations)	Alpha navigation
-	14.881 kHz	Russia (various locations)	Alpha navigation
-	15.625 kHz	-	horizontal line deflection frequency of former tube TV sets without 100 Hz technology (countries with 50 Hz power grid)
-	15.734 kHz	-	horizontal line deflection frequency of tube TV sets without 120 Hz technology (countries with 60 Hz power grid and color television)
-	15.750 kHz	-	Former horizontal line deflection frequency before the introduction of color television (countries with 60 Hz power grid and black and white television)
?	15.8 kHz	?
JXN	16.4 kHz	Helgeland (Norway)
SAQ	17.2 kHz	Grimeton (Sweden)	only active on special occasions ( Alexanderson Day )
-	approx. 17.5 kHz	?	Twenty second pulses
NAA	17.8 kHz	Cutler (USA)	US Navy submarine transmitter
RDL / UPD / UFQE / UPP / UPD8	18.1 kHz	Russia (various locations)
HWU	18.3 kHz	Le Blanc (France)	often inactive for a long time
RKS	18.9 kHz	Russia (various locations)	rarely and only active for a short time
GBZ	19.6 kHz	Anthorn (UK)	large repertoire of operating modes, including impulses
ICV	20.27 kHz	Tavolara (Italy)
RJH63, RJH66, RJH69, RJH77, RJH99	20.5 kHz	Russia (various locations)	Time signal system beta
ICV	20.76 kHz	Tavolara (Italy)
HWU	20.9 kHz	Le Blanc (France)
RDL	21.1 kHz	Russia (various locations)	rarely active
HWU	21.75 kHz	Le Blanc (France)
JJI	22.1 kHz	Marine station Ebino (Japan)
?	22.1 kHz	Skelton (UK)
?	22.3 kHz	Russia?	only on the 2nd of a month from 11 am to 1 pm or 10 am to 12 noon in winter, but not on Sundays.
RJH63, RJH66, RJH69, RJH77, RJH99	23 kHz	Russia (various locations)	Time signal system beta
DHO38	23.4 kHz	Saterland (Germany)	Active transmitter of the German Navy
NAA	24 kHz	Cutler (USA)	US Navy submarine transmitter
TBB	26.7 kHz	Bafa (Turkey)	Transmitter for the longest wave of the US military ( NATO )

The well-known long-wave transmitter GBR in Rugby (transmission frequency: 15.95 kHz) stopped broadcasting on April 1, 2003.

Web links

Wikibooks: Long-wave reception with the PC - learning and teaching materials

Longwave reception with ferrite antennas (PDF, 437 KiB)

Individual evidence

↑ Davies, K., “Ionospheric Radio,” Peregrinus Ltd, London, 1990
↑ Rawer, K., "Wave Propagation in the Ionosphere", Kluwer Publ., Dordrecht, 1993
^ Budden, KG, "The Propagation of Radiowaves", Cambridge, University Press, Cambridge, 1985
↑ The long-wave transmitter Goliath at Kalbe an der Milde from 1941 to 1945 , on: cdvandt.org (PDF; 1.8 MB)

[1] Davies, K., “Ionospheric Radio,” Peregrinus Ltd, London, 1990

[2] Rawer, K., "Wave Propagation in the Ionosphere", Kluwer Publ., Dordrecht, 1993

[3] Budden, KG, "The Propagation of Radiowaves", Cambridge, University Press, Cambridge, 1985

[4] The long-wave transmitter Goliath at Kalbe an der Milde from 1941 to 1945 , on: cdvandt.org (PDF; 1.8 MB)