Hertz

For alternative betydninger, se Hertz (flertydig). (Se også artikler, som begynder med Hertz)

Frekvens måles i den afledte SI-enhed hertz (symbol Hz), der svarer til antallet af svingninger per sekund eller perioder per sekund, dvs. 1 Hz = 1 s^-1 = 1/s.

Radiomodtager fra 1962 hvor der står MHz på FM-båndets skala. På tyske radiomodtagere står der UKW for FM-båndet. Bemærk langbølgebåndet (LW), mellembølgebåndet (MW) og kortbølgebåndet (KW) har skalaer med angivelse i meter (bølgelængden). Klik på billedet for forstørrelse.

Enheden hertz er opkaldt efter den tyske fysiker Heinrich Rudolf Hertz.

Historisk

Klikker man på billedet og ser på FM-båndets skala, ses det at der yderst til højre i det gennemsigtige, står Mc for megacycles [underforstået per second].

Billede af kvartskrystal resonatorer (venstre til højre): ur (32768 Hz), ældre tv farveoscillator (4,433613 MHz), kortbølge 6,55 MHz (Bemærk: Påstemplet 6550,0 kc), 12,8 MHz referencekrystal, 27,095 MHz, 40,675 MHz.

Før 1923 blev frekvensen typisk ikke anvendt eller angivet for radiostationer, det skyldes at radiobølger i radiofoniens barndom, primært refererede til radiobølger ved deres bølgelængde i meter.^[1] Det er den historiske grund til at mange radiobånd stadig angives ved deres bølgelængdebånd. Eksempler; læs i: Kortbølgebånd og radioamatørbånd.

Mellem ca. 1923 til 1960 anbefales det at angive radiobølgers frekvens på dansk cyklusser per sekund^[2] - engelsk cycles per second forkortet til cps eller c/s; f.eks. forkortes kilocycles per second til kcps - og blev forkortet yderligere til kc - og Mc for megacycles [underforstået per second].^[3]

Fra 1960 angives frekvens i Hertz.^[3] Skal man stille ind på en radiostation, angives den ved sin bærebølges frekvens.

Se også

Kilder/referencer

^ earlyradiohistory.us: Kilohertz to Meters Conversion Charts Citat: "...The general public, used to wavelengths, had to be coaxed into making the transition to frequencies, and it was a good fifteen years before you stopped seeing references to wavelengths in the U.S. (In Europe, where mediumwave stations are assigned in 9 khz steps, they still are commonly reported by wavelength). In 1923 many publications started to print conversion charts like the two listed above, with explanations about this newfangled frequency concept. However, there was one area of inconsistency, which explains why I've included two slightly different charts...In the early 1920s, the best estimate for the speed of light was 299,820 kilometers per second. (This was actually a little high--the current accepted value is 299,792.458 kilometers per second). Many people rounded this to an even 300,000, to make the calculations easier. Also, they just reported the result to the nearest whole meter. In contrast, the more precise people, using 299,820, generally carried the result to the nearest tenth of a meter. Thus, in the above charts, 560 kilohertz was said by the 300,000 people to be equal to a wavelength of 536 meters, while the more precise 299,820 crowd came up with 535.4 meters. (Today, armed with a computer and an up-to-date speed-of-light estimate, I'm happy to report that the actual answer is 535.343675 meters [calculated as 299,792.458 divided by 560])...", backup
^ oz5gx.dk: Radioteknik, backup
^ ^a ^b November 18, 2016, edn.com: Cycles per second: A historical perspective Citat: "...In honor of Hertz's many contributions to the field of electrodynamics the General Conference on Weights and Measures (CGPM) in 1960 replaced the designation of cycles-per-second with hertz..."

Spire

Denne artikel om fysik er en spire som bør udbygges. Du er velkommen til at hjælpe Wikipedia ved at udvide den.

[1] rlyradiohistory.us: Kilohertz to Meters Conversion Charts Citat: "...The general public, used to wavelengths, had to be coaxed into making the transition to frequencies, and it was a good fifteen years before you stopped seeing references to wavelengths in the U.S. (In Europe, where mediumwave stations are assigned in 9 khz steps, they still are commonly reported by wavelength). In 1923 many publications started to print conversion charts like the two listed above, with explanations about this newfangled frequency concept. However, there was one area of inconsistency, which explains why I've included two slightly different charts...In the early 1920s, the best estimate for the speed of light was 299,820 kilometers per second. (This was actually a little high--the current accepted value is 299,792.458 kilometers per second). Many people rounded this to an even 300,000, to make the calculations easier. Also, they just reported the result to the nearest whole meter. In contrast, the more precise people, using 299,820, generally carried the result to the nearest tenth of a meter. Thus, in the above charts, 560 kilohertz was said by the 300,000 people to be equal to a wavelength of 536 meters, while the more precise 299,820 crowd came up with 535.4 meters. (Today, armed with a computer and an up-to-date speed-of-light estimate, I'm happy to report that the actual answer is 535.343675 meters [calculated as 299,792.458 divided by 560])...", backup

[2] z5gx.dk: Radioteknik, backup

[CGPM-3] November 18, 2016, edn.com: Cycles per second: A historical perspective Citat: "...In honor of Hertz's many contributions to the field of electrodynamics the General Conference on Weights and Measures (CGPM) in 1960 replaced the designation of cycles-per-second with hertz..."

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