In telecommunications , radio silence or emissions control ( EMCON ) is a status in which all fixed or mobile radio stations in an area are asked to stop transmitting for safety or security reasons.
112-462: The term "radio station" may include anything capable of transmitting a radio signal . A single ship, aircraft, or spacecraft, or a group of them, may also maintain radio silence. The Wilderness Protocol recommends that those stations able to do so should monitor the primary (and secondary, if possible) frequency every three hours starting at 7 AM, local time, for 5 minutes starting at the top of every hour, or even continuously. The Wilderness Protocol
224-412: A microphone , a video signal representing moving images from a video camera , or a digital signal representing data from a computer . In the transmitter, an electronic oscillator generates an alternating current oscillating at a radio frequency , called the carrier wave because it creates the radio waves that "carry" the information through the air. The information signal is used to modulate
336-418: A resonator , similarly to a tuning fork . The tuned circuit has a natural resonant frequency at which it oscillates. The resonant frequency is set equal to the frequency of the desired radio station. The oscillating radio signal from the desired station causes the tuned circuit to oscillate in sympathy, and it passes the signal on to the rest of the receiver. Radio signals at other frequencies are blocked by
448-552: A space heater or wood fire. The oscillating electric field of the wave causes polar molecules to vibrate back and forth, increasing the temperature; this is how a microwave oven cooks food. Radio waves have been applied to the body for 100 years in the medical therapy of diathermy for deep heating of body tissue, to promote increased blood flow and healing. More recently they have been used to create higher temperatures in hyperthermia therapy and to kill cancer cells. However, unlike infrared waves, which are mainly absorbed at
560-509: A transmitter , which is connected to an antenna , which radiates the waves. They are received by another antenna connected to a radio receiver , which processes the received signal. Radio waves are very widely used in modern technology for fixed and mobile radio communication , broadcasting , radar and radio navigation systems, communications satellites , wireless computer networks and many other applications. Different frequencies of radio waves have different propagation characteristics in
672-515: A 250 kg bomb underneath the fuselage, the later model arriving during the battle. The Bf 109, unlike the Stuka , could fight on equal terms with RAF fighters after releasing its ordnance . At the start of the battle, the twin-engined Messerschmitt Bf 110C long-range Zerstörer ("Destroyer") was also expected to engage in air-to-air combat while escorting the Luftwaffe bomber fleet. Although
784-538: A base for the successful prosecution of the air and sea war against England". On 29 November, OKW "Directive No. 9 – Instructions For Warfare Against The Economy Of The Enemy" stated that once this coastline had been secured, the Luftwaffe together with the Kriegsmarine (German Navy) was to blockade UK ports with sea mines. They were to attack shipping and warships and make air attacks on shore installations and industrial production. This directive remained in force in
896-493: A high state of maturity in early 1943 with the aid of United States institutions aiding British Research and Development under the pressures of the continuing Battle of the Atlantic during World War II when locating U-boats. One key breakthrough was marrying MIT/Raytheon developed CRT technology with pairs of RDF antennas giving a differentially derived instant bearing useful in tactical situations, enabling escorts to run down
1008-461: A human user. The radio waves from many transmitters pass through the air simultaneously without interfering with each other. They can be separated in the receiver because each transmitter's radio waves oscillate at a different rate, in other words each transmitter has a different frequency , measured in kilohertz (kHz), megahertz (MHz) or gigahertz (GHz). The bandpass filter in the receiver consists of one or more tuned circuits which act like
1120-557: A last resort once the British economy had been damaged and the Luftwaffe had full air superiority. On 2 July, OKW requested preliminary plans. In Britain, Churchill described "the great invasion scare" as "serving a very useful purpose" by "keeping every man and woman tuned to a high pitch of readiness". Historian Len Deighton stated that on 10 July Churchill advised the War Cabinet that invasion could be ignored, as it "would be
1232-403: A left-hand sense. Right circularly polarized radio waves consist of photons spinning in a right hand sense. Left circularly polarized radio waves consist of photons spinning in a left hand sense. Plane polarized radio waves consist of photons in a quantum superposition of right and left hand spin states. The electric field consists of a superposition of right and left rotating fields, resulting in
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#17327824241151344-567: A more capable opponent than any it had previously met: a sizeable, highly coordinated, well-supplied, modern air force. The Luftwaffe's Messerschmitt Bf 109E and Bf 110C fought against the RAF's workhorse Hurricane Mk I and the less numerous Spitfire Mk I ; Hurricanes outnumbered Spitfires in RAF Fighter Command by about 2:1 when war broke out. The Bf 109E had a better climb rate and was up to 40 mph faster in level flight than
1456-529: A most hazardous and suicidal operation". On 11 July, Hitler agreed with Raeder that invasion would be a last resort, and the Luftwaffe advised that gaining air superiority would take 14 to 28 days. Hitler met his army chiefs, von Brauchitsch and Halder , at the Berchtesgaden on 13 July where they presented detailed plans on the assumption that the navy would provide safe transport. Von Brauchitsch and Halder were surprised that Hitler took no interest in
1568-605: A plane oscillation. Radio waves are more widely used for communication than other electromagnetic waves mainly because of their desirable propagation properties, stemming from their large wavelength . Radio waves have the ability to pass through the atmosphere in any weather, foliage, and through most building materials. By diffraction , longer wavelengths can bend around obstructions, and unlike other electromagnetic waves they tend to be scattered rather than absorbed by objects larger than their wavelength. The study of radio propagation , how radio waves move in free space and over
1680-402: A plane perpendicular to the direction of motion. In a horizontally polarized radio wave the electric field oscillates in a horizontal direction. In a vertically polarized wave the electric field oscillates in a vertical direction. In a circularly polarized wave the electric field at any point rotates about the direction of travel, once per cycle. A right circularly polarized wave rotates in
1792-404: A right-hand sense about the direction of travel, while a left circularly polarized wave rotates in the opposite sense. The wave's magnetic field is perpendicular to the electric field, and the electric and magnetic field are oriented in a right-hand sense with respect to the direction of radiation. An antenna emits polarized radio waves, with the polarization determined by the direction of
1904-446: A similar proposal; when rebuffed, he told Churchill that interference with German domination would mean war. To Hitler's great annoyance, all his diplomacy failed to stop Britain from declaring war when he invaded Poland. During the fall of France, he repeatedly discussed peace efforts with his generals. When Churchill came to power, there was still wide support for Halifax, who as Foreign Secretary openly argued for peace negotiations in
2016-446: A study (in 1939) on the possibility of an invasion of Britain and concluded that it also required naval superiority. The Luftwaffe said invasion could only be "the final act in an already victorious war." Hitler first discussed the idea of an invasion at a 21 May 1940 meeting with Grand Admiral Erich Raeder, who stressed the difficulties and his own preference for a blockade. OKW Chief of Staff Jodl's 30 June report described invasion as
2128-643: A surprise to the Jagdwaffe , although the German pilots retained a strong belief that the 109 was the superior fighter. The British fighters were equipped with eight Browning .303 (7.7mm) machine guns while most Bf 109Es had two 20mm cannons supplemented by two 7.92mm machine guns. The 20mm cannons were much more effective than the .303; during the Battle it was not unknown for damaged German bombers to limp home with up to two hundred .303 hits. At some altitudes,
2240-659: A waste of strategic effort. The defeat of France in June 1940 introduced the prospect for the first time of independent air action against Britain. A July Fliegercorps I paper asserted that Germany was by definition an air power: "Its chief weapon against England is the Air Force, then the Navy, followed by the landing forces and the Army." In 1940, the Luftwaffe would undertake a " strategic offensive ... on its own and independent of
2352-457: Is 0. Impose radio silence. Over. Other countermeasures are also applied to protect secrets against enemy signals intelligence . Electronic emissions can be used to plot a line of bearing to an intercepted signal, and if more than one receiver detects it, triangulation can estimate its location. Radio direction finding (RDF) was critically important during the Battle of Britain and reached
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#17327824241152464-404: Is absorbed within a few meters, so the atmosphere is effectively opaque. In radio communication systems, information is transported across space using radio waves. At the sending end, the information to be sent, in the form of a time-varying electrical signal, is applied to a radio transmitter . The information, called the modulation signal , can be an audio signal representing sound from
2576-591: Is also defeated, the fundamental conditions for a successful war against England will have been secured. England can then be blockaded from Western France at close quarters by the Air Force, while the Navy with its submarines extend the range of the blockade." When war commenced, Hitler and the OKW ( Oberkommando der Wehrmacht or "High Command of the Armed Forces") issued a series of directives ordering, planning and stating strategic objectives. "Directive No. 1 for
2688-541: Is derived from the This was their finest hour speech delivered by Winston Churchill in the House of Commons on 18 June, more than three weeks prior to the generally accepted date for the start of the battle: ... What General Weygand called the Battle of France is over. I expect that the battle of Britain is about to begin. Upon this battle depends the survival of Christian civilization. Upon it depends our own British life and
2800-442: Is extremely small, from 10 to 10 joules . So the antenna of even a very low power transmitter emits an enormous number of photons every second. Therefore, except for certain molecular electron transition processes such as atoms in a maser emitting microwave photons, radio wave emission and absorption is usually regarded as a continuous classical process, governed by Maxwell's equations . Radio waves in vacuum travel at
2912-425: Is finished, the controlling station lifts radio silence by the prowords "Seelonce FINI." Disobeying a Seelonce Mayday order constitutes a serious criminal offence in most countries. The aviation equivalent of Seelonce Mayday is the phrase or command "Stop Transmitting - Distress (or Mayday)". "Distress traffic ended" is the phrase used when the emergency is over. Again, disobeying such an order is extremely dangerous and
3024-576: Is now included in both the ARRL ARES Field Resources Manual and the ARES Emergency Resources Manual. Per the manual, the protocol is: The Wilderness protocol (see page 101, August 1995 QST) calls for hams in the wilderness to announce their presence on, and to monitor, the national calling frequencies for five minutes beginning at the top of the hour, every three hours from 7 AM to 7 PM while in
3136-577: Is reserved to me. Attacks on the English homeland are to be prepared, bearing in mind that inconclusive results with insufficient forces are to be avoided in all circumstances. Both France and the UK declared war on Germany; on 9 October, Hitler's "Directive No. 6" planned the offensive to defeat these allies and "win as much territory as possible in the Netherlands, Belgium, and northern France to serve as
3248-453: Is temporarily pointed away from Earth in order to perform observations, or there is insufficient power to operate the radio transmitter, or during re-entry when the hot plasma surrounding the spacecraft blocks radio signals. In the USA , CONELRAD and EBS (which are now discontinued), and EAS (which is currently active) are also ways of maintaining radio silence, mainly in broadcasting , in
3360-621: Is the only authority to impose or lift radio silence either fully or selectively. The lifting of radio silence can only be ordered on the authority of the HQ that imposed it in the first place. During periods of radio silence a station may, with justifiable cause, transmit a message. This is known as Breaking Radio Silence. The necessary replies are permitted but radio silence is automatically re-imposed afterwards. The breaking station transmits its message using BATCO to break radio silence. The command for imposing radio silence is: Hello all stations, this
3472-426: Is the wavelength of a 1 hertz radio signal. A 1 megahertz radio wave (mid- AM band ) has a wavelength of 299.79 meters (983.6 ft). Like other electromagnetic waves, a radio wave has a property called polarization , which is defined as the direction of the wave's oscillating electric field perpendicular to the direction of motion. A plane-polarized radio wave has an electric field that oscillates in
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3584-482: Is therefore a criminal offence in most countries. Up until the procedure was replaced by the Global Maritime Distress and Safety System (August 1, 2013 in the U.S.), maritime radio stations were required to observe radio silence on 500 kHz (radiotelegraph) for the three minutes between 15 and 18 minutes past the top of each hour, and for the three minutes between 45 and 48 minutes past the top of
3696-400: Is weak mechanistic evidence of cancer risk via personal exposure to RF-EMF from mobile telephones. Radio waves can be shielded against by a conductive metal sheet or screen, an enclosure of sheet or screen is called a Faraday cage . A metal screen shields against radio waves as well as a solid sheet as long as the holes in the screen are smaller than about 1 ⁄ 20 of wavelength of
3808-526: The Luftwaffe was formally announced, with Walther Wever as Chief of Staff. The 1935 Luftwaffe doctrine for "Conduct of Air War" ( Luftkriegführung ) set air power within the overall military strategy, with critical tasks of attaining (local and temporary) air superiority and providing battlefield support for army and naval forces. Strategic bombing of industries and transport could be decisive longer-term options, dependent on opportunity or preparations by
3920-497: The military where any radio transmission may reveal troop positions, either audibly from the sound of talking, or by radio direction finding . In extreme scenarios Electronic Silence ('Emissions Control' or EMCON) may also be put into place as a defence against interception. In the British Army , the imposition and lifting of radio silence will be given in orders or ordered by control using 'Battle Code' ( BATCO ). Control
4032-467: The speed of light c {\displaystyle c} . When passing through a material medium, they are slowed depending on the medium's permeability and permittivity . Air is tenuous enough that in the Earth's atmosphere radio waves travel at very nearly the speed of light. The wavelength λ {\displaystyle \lambda } is the distance from one peak (crest) of
4144-428: The speed of light , and in the Earth's atmosphere at a slightly lower speed. Radio waves are generated by charged particles undergoing acceleration , such as time-varying electric currents . Naturally occurring radio waves are emitted by lightning and astronomical objects , and are part of the blackbody radiation emitted by all warm objects. Radio waves are generated artificially by an electronic device called
4256-482: The "near field" zone, the physical relationships between the electric and magnetic components of the field can be complex, and it is best to use the field strength units discussed above. Power density is measured in terms of power per unit area, for example, with the unit milliwatt per square centimeter (mW/cm ). When speaking of frequencies in the microwave range and higher, power density is usually used to express intensity since exposures that might occur would likely be in
4368-467: The 1909 Nobel Prize in physics for his radio work. Radio communication began to be used commercially around 1900. The modern term " radio wave " replaced the original name " Hertzian wave " around 1912. Radio waves are radiated by charged particles when they are accelerated . Natural sources of radio waves include radio noise produced by lightning and other natural processes in the Earth's atmosphere, and astronomical radio sources in space such as
4480-585: The Battle period he sought neutrality or a peace treaty with Britain. In a secret conference on 23 May 1939, Hitler set out his rather contradictory strategy that an attack on Poland was essential and "will only be successful if the Western Powers keep out of it. If this is impossible, then it will be better to attack in the West and to settle Poland at the same time" with a surprise attack. "If Holland and Belgium are successfully occupied and held, and if France
4592-595: The Bf 109 could outclimb the British fighter. It could also engage in vertical-plane negative- g manoeuvres without the engine cutting out because its DB 601 engine used fuel injection ; this allowed the 109 to dive away from attackers more readily than the carburettor -equipped Merlin. On the other hand, the Bf 109E had a much larger turning circle than its two foes. In general, though, as Alfred Price noted in The Spitfire Story : ... the differences between
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4704-538: The British Foreign Secretary , Lord Halifax , and certain elements of the British public favoured a negotiated peace with an ascendant Germany, Churchill and a majority of his Cabinet refused to consider an armistice. Instead, Churchill used his skilful rhetoric to harden public opinion against capitulation and prepare the British for a long war. The Battle of Britain has the unusual distinction that it gained its name before being fought. The name
4816-527: The British trade". Instead of the Wehrmacht attacking the French, the Luftwaffe with naval assistance was to block imports to Britain and attack seaports. "Should the enemy resort to terror measures – for example, to attack our towns in western Germany" they could retaliate by bombing industrial centres and London. Parts of this appeared on 29 November in "Directive No. 9" as future actions once
4928-551: The Channel. In September, RAF Bomber Command night raids disrupted the German preparation of converted barges, and the Luftwaffe's failure to overwhelm the RAF forced Hitler to postpone and eventually cancel Operation Sea Lion. The Luftwaffe proved unable to sustain daylight raids, but their continued night-bombing operations on Britain became known as the Blitz. Germany's failure to destroy Britain's air defences and force it out of
5040-632: The Conduct of the War", dated 31 August 1939, instructed the invasion of Poland on 1 September as planned . Potentially, Luftwaffe "operations against England" were to: dislocate English imports, the armaments industry, and the transport of troops to France. Any favourable opportunity of an effective attack on concentrated units of the English Navy, particularly on battleships or aircraft carriers, will be exploited. The decision regarding attacks on London
5152-447: The Earth's atmosphere; long waves can diffract around obstacles like mountains and follow the contour of the Earth ( ground waves ), shorter waves can reflect off the ionosphere and return to Earth beyond the horizon ( skywaves ), while much shorter wavelengths bend or diffract very little and travel on a line of sight , so their propagation distances are limited to the visual horizon. To prevent interference between different users,
5264-461: The French surrender on 22 June 1940, Hitler mainly focused his energies on the possibility of invading the Soviet Union . He believed that the British, defeated on the continent and without European allies, would quickly come to terms. The Germans were so convinced of an imminent armistice that they began constructing street decorations for the homecoming parades of victorious troops. Although
5376-675: The Low Countries in the Battle of France , leaving Britain to face the threat of invasion by sea. The German high command recognised the difficulties of a seaborne attack while the Royal Navy controlled the English Channel and the North Sea . On 16 July, Hitler ordered the preparation of Operation Sea Lion as a potential amphibious and airborne assault on Britain, to follow once the Luftwaffe had air superiority over
5488-403: The Luftwaffe lacked the means to do much damage to Britain's war economy beyond laying naval mines . Joseph Schmid , in charge of Luftwaffe intelligence, presented a report on 22 November 1939, stating that, "Of all Germany's possible enemies, Britain is the most dangerous." This "Proposal for the Conduct of Air Warfare" argued for a counter to the British blockade and said "Key is to paralyse
5600-604: The Luftwaffe mainly targeting coastal-shipping convoys, as well as ports and shipping centres such as Portsmouth . On 1 August, the Luftwaffe was directed to achieve air superiority over the RAF, with the aim of incapacitating RAF Fighter Command ; 12 days later , it shifted the attacks to RAF airfields and infrastructure . As the battle progressed, the Luftwaffe also targeted factories involved in aircraft production and strategic infrastructure. Eventually, it employed terror bombing on areas of political significance and on civilians. The Germans had rapidly overwhelmed France and
5712-850: The Minister in charge of Defence Coordination, Sir Thomas Inskip , sided with Dowding that "The role of our air force is not an early knock-out blow" but rather was "to prevent the Germans from knocking us out" and fighter squadrons were just as necessary as bomber squadrons. The Spanish Civil War (1936–1939) gave the Luftwaffe Condor Legion the opportunity to test air fighting tactics with their new aeroplanes. Wolfram von Richthofen became an exponent of air power providing ground support to other services. The difficulty of accurately hitting targets prompted Ernst Udet to require that all new bombers had to be dive bombers , and led to
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#17327824241155824-522: The OKW reviewed the potential for an air- and seaborne invasion of Britain: the Kriegsmarine was faced with the threat the Royal Navy's larger Home Fleet posed to a crossing of the English Channel , and together with the German Army viewed control of airspace as a necessary precondition. The German navy thought air superiority alone was insufficient; the German naval staff had already produced
5936-477: The Rotol (constant speed propeller) equipped Hurricane Mk I, depending on altitude. The speed and climb disparity with the original non-Rotol Hurricane was even greater. By mid-1940, all RAF Spitfire and Hurricane fighter squadrons converted to 100 octane aviation fuel, which allowed their Merlin engines to generate significantly more power and an approximately 30 mph increase in speed at low altitudes through
6048-535: The Soviet Union. Erhard Milch organised rapid expansion, and following the 1933 Nazi seizure of power , his subordinate Robert Knauss formulated a deterrence theory incorporating Douhet's ideas and Tirpitz's "risk theory" . This proposed a fleet of heavy bombers to deter a preventive attack by France and Poland before Germany could fully rearm. A 1933–34 war game indicated a need for fighters and anti-aircraft protection as well as bombers. On 1 March 1935,
6160-619: The Spitfire and the Me 109 in performance and handling were only marginal, and in a combat they were almost always surmounted by tactical considerations of which side had seen the other first, which had the advantage of sun, altitude, numbers, pilot ability, tactical situation, tactical co-ordination, amount of fuel remaining, etc. The Bf 109E was also used as a Jabo ( jagdbomber , fighter-bomber ) – the E-4/B and E-7 models could carry
6272-463: The Sun, galaxies and nebulas. All warm objects radiate high frequency radio waves ( microwaves ) as part of their black body radiation . Radio waves are produced artificially by time-varying electric currents , consisting of electrons flowing back and forth in a specially shaped metal conductor called an antenna . An electronic device called a radio transmitter applies oscillating electric current to
6384-481: The abyss of a new Dark Age made more sinister, and perhaps more protracted, by the lights of a perverted science. Let us therefore brace ourselves to our duties, and so bear ourselves that, if the British Empire and its Commonwealth last for a thousand years, men will still say, "This was their finest hour". From the outset of his rise to power, Adolf Hitler expressed admiration for Britain, and throughout
6496-540: The antenna, and the antenna radiates the power as radio waves. Radio waves are received by another antenna attached to a radio receiver . When radio waves strike the receiving antenna they push the electrons in the metal back and forth, creating tiny oscillating currents which are detected by the receiver. From quantum mechanics , like other electromagnetic radiation such as light, radio waves can alternatively be regarded as streams of uncharged elementary particles called photons . In an antenna transmitting radio waves,
6608-433: The army and navy. It could be used to overcome a stalemate, or used when only destruction of the enemy's economy would be conclusive. The list excluded bombing civilians to destroy homes or undermine morale, as that was considered a waste of strategic effort, but the doctrine allowed revenge attacks if German civilians were bombed. A revised edition was issued in 1940, and the continuing central principle of Luftwaffe doctrine
6720-657: The artificial generation and use of radio waves is strictly regulated by law, coordinated by an international body called the International Telecommunication Union (ITU), which defines radio waves as " electromagnetic waves of frequencies arbitrarily lower than 3000 GHz , propagated in space without artificial guide". The radio spectrum is divided into a number of radio bands on the basis of frequency, allocated to different uses. Higher-frequency, shorter-wavelength radio waves are called microwaves . Radio waves were first predicted by
6832-502: The back country. A ham in a remote location may be able to relay emergency information through another wilderness ham who has better access to a repeater. National calling frequencies: 52.525, 146.52, 223.50, 446.00, 1294.50 MHz. Priority transmissions should begin with the LITZ (Long Interval Tone Zero or Long Time Zero) DTMF signal for at least 5 seconds. CQ like calls (to see who is out there) should not take place until after 4 minutes after
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#17327824241156944-655: The bearing to an intercept. The U-boat command of Wolfpacks required a minimum once daily communications check-in , allowing new Hunter-Killer groups to localize U-boats tactically from April on, leading to dramatic swings in the fortunes of war in the battles between March, when the U-boats sank over 300 allied ships and "Black May" when the allies sank at least 44 U-boats—each without orders to exercise EMCON/radio silence. Radio silence can be maintained for other purposes, such as for highly sensitive radio astronomy . Radio silence can also occur for spacecraft whose antenna
7056-410: The carrier, altering some aspect of it, encoding the information on the carrier. The modulated carrier is amplified and applied to an antenna . The oscillating current pushes the electrons in the antenna back and forth, creating oscillating electric and magnetic fields , which radiate the energy away from the antenna as radio waves. The radio waves carry the information to the receiver location. At
7168-509: The coast had been conquered. On 24 May 1940 "Directive No. 13" authorised attacks on the blockade targets, as well as retaliation for RAF bombing of industrial targets in the Ruhr. After the defeat of France, the OKW felt they had won the war, and some more pressure would persuade Britain to give in. On 30 June, the OKW Chief of Staff Alfred Jodl issued his paper setting out options: the first
7280-402: The conduct of air and sea warfare against England" issued on 1 August attempted to keep all the options open. The Luftwaffe's Adlertag campaign was to start around 5 August, subject to weather, with the aim of gaining air superiority over southern England as a necessary precondition of invasion, to give credibility to the threat and give Hitler the option of ordering the invasion. The intention
7392-439: The continent, and on 30 June the OKW Chief of Staff, Alfred Jodl , issued his review of options to increase pressure on Britain to agree to a negotiated peace. The first priority was to eliminate the RAF and gain air supremacy. Intensified air attacks against shipping and the economy could affect food supplies and civilian morale in the long term. Reprisal attacks of terror bombing had the potential to cause quicker capitulation, but
7504-536: The continuing influence of the 1935 "Conduct of the Air War" doctrine, the main focus of the Luftwaffe command (including Göring) was in concentrating attacks to destroy enemy armed forces on the battlefield, and "blitzkrieg" close air support of the army succeeded brilliantly. They reserved strategic bombing for a stalemate situation or revenge attacks, but doubted if this could be decisive on its own and regarded bombing civilians to destroy homes or undermine morale as
7616-682: The defending armies in Norway in early 1940 created a significant political crisis in Britain. In early May 1940, the Norway Debate questioned the fitness for office of the British Prime Minister Neville Chamberlain . On 10 May, the same day Winston Churchill became British Prime Minister, the Germans initiated the Battle of France with an aggressive invasion of French territory. RAF Fighter Command
7728-618: The development of the Knickebein system for night time navigation. Priority was given to producing large numbers of smaller aeroplanes, and plans for a long-range, four-engined strategic bomber were cancelled. The early stages of the Second World War saw successful German invasions on the continent, aided decisively by the air power of the Luftwaffe, which was able to establish tactical air superiority with great effectiveness. The speed with which German forces defeated most of
7840-536: The effect on morale was uncertain. On the same day, the Luftwaffe Commander-in-Chief, Hermann Göring issued his operational directive: to destroy the RAF, thus protecting German industry, and also to block overseas supplies to Britain. The German Supreme Command argued over the practicality of these options. In "Directive No. 16 – On preparations for a landing operation against England" on 16 July, Hitler required readiness by mid-August for
7952-421: The electrons in the antenna emit the energy in discrete packets called radio photons, while in a receiving antenna the electrons absorb the energy as radio photons. An antenna is a coherent emitter of photons, like a laser , so the radio photons are all in phase . However, from Planck's relation E = h ν {\displaystyle E=h\nu } , the energy of individual radio photons
8064-438: The energy is deposited. For example, the 2.45 GHz radio waves (microwaves) in a microwave oven penetrate most foods approximately 2.5 to 3.8 cm . Looking into a source of radio waves at close range, such as the waveguide of a working radio transmitter, can cause damage to the lens of the eye by heating. A strong enough beam of radio waves can penetrate the eye and heat the lens enough to cause cataracts . Since
8176-553: The event of an attack. Radio signal Radio waves are a type of electromagnetic radiation with the lowest frequencies and the longest wavelengths in the electromagnetic spectrum , typically with frequencies below 300 gigahertz (GHz) and wavelengths greater than 1 millimeter ( 3 ⁄ 64 inch), about the diameter of a grain of rice. Radio waves with frequencies above about 1 GHz and wavelengths shorter than 30 centimeters are called microwaves . Like all electromagnetic waves, radio waves in vacuum travel at
8288-1075: The far field zone. ELF 3 Hz/100 Mm 30 Hz/10 Mm SLF 30 Hz/10 Mm 300 Hz/1 Mm ULF 300 Hz/1 Mm 3 kHz/100 km VLF 3 kHz/100 km 30 kHz/10 km LF 30 kHz/10 km 300 kHz/1 km MF 300 kHz/1 km 3 MHz/100 m HF 3 MHz/100 m 30 MHz/10 m VHF 30 MHz/10 m 300 MHz/1 m UHF 300 MHz/1 m 3 GHz/100 mm SHF 3 GHz/100 mm 30 GHz/10 mm EHF 30 GHz/10 mm 300 GHz/1 mm THF 300 GHz/1 mm 3 THz/0.1 mm Battle of Britain Asia-Pacific Mediterranean and Middle East Other campaigns Coups Luxembourg The Netherlands Belgium France Britain 1941–1943 1944–1945 Germany Strategic campaigns The Battle of Britain ( German : Luftschlacht um England , lit. 'air battle for England')
8400-621: The first independent strategic bombing campaign. Hitler's 1925 book Mein Kampf mostly set out his hatreds: he only admired ordinary German World War I soldiers and Britain, which he saw as an ally against communism. In 1935 Hermann Göring welcomed news that Britain, as a potential ally, was rearming. In 1936 he promised assistance to defend the British Empire, asking only a free hand in Eastern Europe, and repeated this to Lord Halifax in 1937. That year, von Ribbentrop met Churchill with
8512-475: The first phase of the Battle of Britain. It was reinforced on 24 May during the Battle of France by "Directive No. 13", which authorised the Luftwaffe "to attack the English homeland in the fullest manner, as soon as sufficient forces are available. This attack will be opened by an annihilating reprisal for English attacks on the Ruhr Basin." By the end of June 1940, Germany had defeated Britain's allies on
8624-527: The heating effect is in principle no different from other sources of heat, most research into possible health hazards of exposure to radio waves has focused on "nonthermal" effects; whether radio waves have any effect on tissues besides that caused by heating. Radiofrequency electromagnetic fields have been classified by the International Agency for Research on Cancer (IARC) as having "limited evidence" for its effects on humans and animals. There
8736-407: The hour. Radio silence can be used in nautical and aeronautical communications to allow faint distress calls to be heard (see Mayday ). In the latter case, the controlling station can order other stations to stop transmitting with the proword "Seelonce Seelonce Seelonce". (The word uses an approximation of the French pronunciation of the word silence, "See-LAWNCE."). Once the need for radio silence
8848-415: The hour; and were also required to observe radio silence on 2182 kHz (upper-sideband radiotelephony) for the first three minutes of each hour (H+00 to H+03) and for the three minutes following the bottom of the hour (H+30 to H+33). For 2182 kHz, this is still a legal requirement, according to 47 CFR 80.304 - Watch requirement during silence periods. An order for Radio silence is generally issued by
8960-473: The invasion plans, unlike his usual attitude toward military operations, but on 16 July he issued Directive No. 16, ordering preparations for Operation Sea Lion. The navy insisted on a narrow beachhead and an extended period for landing troops; the army rejected these plans: the Luftwaffe could begin an air attack in August. Hitler held a meeting of his army and navy chiefs on 31 July. The navy said 22 September
9072-467: The levels of electric and magnetic field strength at a measurement location. Another commonly used unit for characterizing an RF electromagnetic field is power density . Power density is most accurately used when the point of measurement is far enough away from the RF emitter to be located in what is referred to as the far field zone of the radiation pattern. In closer proximity to the transmitter, i.e., in
9184-516: The long continuity of our institutions and our Empire . The whole fury and might of the enemy must very soon be turned on us. Hitler knows that he will have to break us in this island or lose the war. If we can stand up to him, all Europe may be free and the life of the world may move forward into broad, sunlit uplands. But if we fail, then the whole world, including the United States, including all that we have known and cared for, will sink into
9296-528: The merger of the British army and navy air services into the Royal Air Force (RAF). Its first Chief of the Air Staff , Hugh Trenchard , was among the military strategists in the 1920s, like Giulio Douhet , who saw air warfare as a new way to overcome the bloody stalemate of trench warfare . Interception was expected to be nearly impossible, with fighter planes no faster than bombers. Their slogan
9408-434: The metal antenna elements. For example, a dipole antenna consists of two collinear metal rods. If the rods are horizontal, it radiates horizontally polarized radio waves, while if the rods are vertical, it radiates vertically polarized waves. An antenna receiving the radio waves must have the same polarization as the transmitting antenna, or it will suffer a severe loss of reception. Many natural sources of radio waves, such as
9520-430: The other radio signals picked up by the antenna, then amplifies the signal so it is stronger, then finally extracts the information-bearing modulation signal in a demodulator . The recovered signal is sent to a loudspeaker or earphone to produce sound, or a television display screen to produce a visible image, or other devices. A digital data signal is applied to a computer or microprocessor , which interacts with
9632-521: The other services", according to an April 1944 German account of their military mission. Göring was convinced that strategic bombing could win objectives that were beyond the army and navy, and gain political advantages in the Third Reich for the Luftwaffe and himself. He expected air warfare to decisively force Britain to negotiate, as all in the OKW hoped, and the Luftwaffe took little interest in planning to support an invasion. The Luftwaffe faced
9744-425: The period of large-scale night attacks known as the Blitz , that lasted from 7 September 1940 to 11 May 1941. German historians do not follow this subdivision and regard the battle as a single campaign lasting from July 1940 to May 1941, including the Blitz. The primary objective of the German forces was to compel Britain to agree to a negotiated peace settlement . In July 1940, the air and sea blockade began, with
9856-412: The possibility of an invasion he called Operation Sea Lion , unless the British agreed to negotiations. The Luftwaffe reported that it would be ready to launch its major attack early in August. The Kriegsmarine Commander-in-Chief, Grand Admiral Erich Raeder , continued to highlight the impracticality of these plans and said sea invasion could not take place before early 1941. Hitler now argued that Britain
9968-401: The range of practical radio communication systems decreases with increasing frequency. Below about 20 GHz atmospheric attenuation is mainly due to water vapor. Above 20 GHz, in the millimeter wave band, other atmospheric gases begin to absorb the waves, limiting practical transmission distances to a kilometer or less. Above 300 GHz, in the terahertz band , virtually all the power
10080-421: The reality of Maxwell's electromagnetic waves by experimentally generating electromagnetic waves lower in frequency than light, radio waves, in his laboratory, showing that they exhibited the same wave properties as light: standing waves , refraction , diffraction , and polarization . Italian inventor Guglielmo Marconi developed the first practical radio transmitters and receivers around 1894–1895. He received
10192-446: The receiver, the oscillating electric and magnetic fields of the incoming radio wave push the electrons in the receiving antenna back and forth, creating a tiny oscillating voltage which is a weaker replica of the current in the transmitting antenna. This voltage is applied to the radio receiver , which extracts the information signal. The receiver first uses a bandpass filter to separate the desired radio station's radio signal from all
10304-416: The sun, stars and blackbody radiation from warm objects, emit unpolarized waves, consisting of incoherent short wave trains in an equal mixture of polarization states. The polarization of radio waves is determined by a quantum mechanical property of the photons called their spin . A photon can have one of two possible values of spin; it can spin in a right-hand sense about its direction of motion, or in
10416-412: The surface of objects and cause surface heating, radio waves are able to penetrate the surface and deposit their energy inside materials and biological tissues. The depth to which radio waves penetrate decreases with their frequency, and also depends on the material's resistivity and permittivity ; it is given by a parameter called the skin depth of the material, which is the depth within which 63% of
10528-588: The surface of the Earth, is vitally important in the design of practical radio systems. Radio waves passing through different environments experience reflection , refraction , polarization , diffraction , and absorption . Different frequencies experience different combinations of these phenomena in the Earth's atmosphere, making certain radio bands more useful for specific purposes than others. Practical radio systems mainly use three different techniques of radio propagation to communicate: At microwave frequencies, atmospheric gases begin absorbing radio waves, so
10640-437: The theory of electromagnetism that was proposed in 1867 by Scottish mathematical physicist James Clerk Maxwell . His mathematical theory, now called Maxwell's equations , predicted that a coupled electric and magnetic field could travel through space as an " electromagnetic wave ". Maxwell proposed that light consisted of electromagnetic waves of very short wavelength. In 1887, German physicist Heinrich Hertz demonstrated
10752-579: The tradition of British diplomacy, to secure British independence without war. On 20 May, Halifax secretly requested a Swedish businessman to make contact with Göring to open negotiations. Shortly afterwards, in the May 1940 War Cabinet Crisis , Halifax argued for negotiations involving the Italians, but this was rejected by Churchill with majority support. An approach made through the Swedish ambassador on 22 June
10864-411: The tuned circuit and not passed on. Radio waves are non-ionizing radiation , which means they do not have enough energy to separate electrons from atoms or molecules , ionizing them, or break chemical bonds , causing chemical reactions or DNA damage . The main effect of absorption of radio waves by materials is to heat them, similarly to the infrared waves radiated by sources of heat such as
10976-427: The use of an Emergency Boost Override . In September 1940, the more powerful Mk IIa series 1 Hurricanes started entering service in small numbers. This version was capable of a maximum speed of 342 mph (550 km/h), some 20 mph more than the original (non-Rotol) Mk I, though it was still 15 to 20 mph slower than a Bf 109 (depending on altitude). The performance of the Spitfire over Dunkirk came as
11088-441: The war was the first major German defeat in the Second World War. The Battle of Britain takes its name from the speech given by Prime Minister Winston Churchill to the House of Commons on 18 June: "What General Weygand called the 'Battle of France' is over. I expect that the Battle of Britain is about to begin." Strategic bombing during World War I introduced air attacks intended to panic civilian targets and led in 1918 to
11200-420: The wave's electric field to the next, and is inversely proportional to the frequency f {\displaystyle f} of the wave. The relation of frequency and wavelength in a radio wave traveling in vacuum or air is where Equivalently, c {\displaystyle c} , the distance that a radio wave travels in vacuum in one second, is 299,792,458 meters (983,571,056 ft), which
11312-442: The waves. Since radio frequency radiation has both an electric and a magnetic component, it is often convenient to express intensity of radiation field in terms of units specific to each component. The unit volt per meter (V/m) is used for the electric component, and the unit ampere per meter (A/m) is used for the magnetic component. One can speak of an electromagnetic field , and these units are used to provide information about
11424-687: Was a military campaign of the Second World War , in which the Royal Air Force (RAF) and the Fleet Air Arm (FAA) of the Royal Navy defended the United Kingdom (UK) against large-scale attacks by Nazi Germany 's air force, the Luftwaffe . It was the first major military campaign fought entirely by air forces. The British officially recognise the battle's duration as being from 10 July until 31 October 1940, which overlaps
11536-622: Was desperately short of trained pilots and aircraft. Churchill sent fighter squadrons, the Air Component of the British Expeditionary Force , to support operations in France, where the RAF suffered heavy losses. This was despite the objections of its commander Hugh Dowding that the diversion of his forces would leave home defences under-strength. After the evacuation of British and French soldiers from Dunkirk and
11648-560: Was forbidden a military air force by the 1919 Treaty of Versailles , and therefore air crew were trained by means of civilian and sport flying . Following a 1923 memorandum, the Deutsche Luft Hansa airline developed designs for aircraft such as the Junkers Ju 52 , which could carry passengers and freight, but also be readily adapted into a bomber. In 1926, the secret Lipetsk fighter-pilot school began training Germans in
11760-407: Was holding out in hope of assistance from Russia, and the Soviet Union was to be invaded by mid 1941. Göring met his air fleet commanders, and on 24 July issued "Tasks and Goals" of firstly gaining air supremacy, secondly protecting invasion forces and attacking the Royal Navy's ships. Thirdly, they were to blockade imports, bombing harbours and stores of supplies. Hitler's "Directive No. 17 – For
11872-532: Was received in silence, but he did not suggest negotiations and this was perceived as being effectively an ultimatum by the British government, which rejected the offer. Halifax kept trying to arrange peace until he was sent to Washington in December as ambassador, and in January 1941 Hitler expressed continued interest in negotiating peace with Britain. A May 1939 planning exercise by Luftflotte 3 found that
11984-651: Was reported to Hitler, making peace negotiations seem feasible. Throughout July, as the battle started, the Germans made wider attempts to find a diplomatic solution. On 2 July, the day the armed forces were asked to start preliminary planning for an invasion, Hitler got von Ribbentrop to draft a speech offering peace negotiations. On 19 July Hitler made this speech to the German Parliament in Berlin, appealing "to reason and common sense", and said he could "see no reason why this war should go on". His sombre conclusion
12096-467: Was that the bomber will always get through , and that the only defence was a deterrent bomber force capable of matching retaliation. Predictions were made that a bomber offensive would quickly cause thousands of deaths and civilian hysteria leading to capitulation. However, widespread pacifism following the horrors of the First World War contributed to a reluctance to provide resources. Germany
12208-546: Was that destruction of enemy armed forces was of primary importance. The RAF responded to Luftwaffe developments with its 1934 Expansion Plan A rearmament scheme, and in 1936 it was restructured into Bomber Command , Coastal Command , Training Command and Fighter Command . The last was under Hugh Dowding , who opposed the doctrine that bombers were unstoppable: the invention of radar at that time could allow early detection, and prototype monoplane fighters were significantly faster. Priorities were disputed, but in December 1937,
12320-467: Was the earliest possible date and proposed postponement until the following year, but Hitler preferred September. He then told von Brauchitsch and Halder that he would decide on the landing operation eight to fourteen days after the air attack began. On 1 August, he issued Directive No. 17 for intensified air and sea warfare, to begin with Adlertag on or after 5 August, subject to weather, keeping options open for negotiated peace or blockade and siege. Under
12432-428: Was to incapacitate the RAF so much that the UK would feel open to air attack, and would begin peace negotiations. It was also to isolate the UK and damage war production, beginning an effective blockade. Following severe Luftwaffe losses, Hitler agreed at a 14 September OKW conference that the air campaign was to intensify regardless of invasion plans. On 16 September, Göring gave the order for this change in strategy, to
12544-497: Was to increase attacks on shipping, economic targets and the RAF: air attacks and food shortages were expected to break morale and lead to capitulation. Destruction of the RAF was the first priority, and invasion would be a last resort. Göring's operational directive issued the same day ordered the destruction of the RAF to clear the way for attacks cutting off seaborne supplies to Britain. It made no mention of invasion. In November 1939,
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