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Frequency is a measure of the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency. The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency.

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Wikipedia about frequencies

Frequency is a measure of the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency. The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency.

Definitions and units

For cyclical processes, such as rotation, oscillations, or waves, frequency is defined as a number of cycles, or periods, per unit time. In physics and engineering disciplines, such as optics, acoustics, and radio, frequency is usually denoted by a Latin letter f or by a Greek letter ν (nu).

In SI units, the unit of frequency is hertz (Hz), named after the German physicist Heinrich Hertz. For example, 1 Hz means that an event repeats once per second, 2 Hz is twice per second, and so on . This unit was originally called a cycle per second (cps), which is still sometimes used. Heart rate and musical tempo are measured in beats per minute (BPM). Frequency of rotation is often expressed as a number of revolutions per minute (rpm). BPM and rpm values must be divided by 60 to obtain the corresponding value in Hz: thus, 60 BPM translates into 1 Hz.

The period is usually denoted as T, and is the reciprocal of the frequency f:

T = \frac{1}{f}. The SI (as well as English) unit for period is the second (s).

By timing

To calculate the frequency of an event, the number of occurrences of the event within a fixed time interval are counted, and then divided by the length of the time interval.

In experimental work (for example, calculating the frequency of an oscillating pendulum) it is more accurate to measure the time taken for a fixed number of occurrences, rather than the number of occurrences within a fixed time. The latter method introduces — if N is the number of counted occurrences — a random error between zero and one count, so on average half a count, causing an biased underestimation of f by ½ f / (N + ½)Fact: date=August 2008 in its expected value. In the first method, which is more accurate, frequency is still calculated by dividing the number of occurrences by the time interval; however it is the number of occurrences that is fixed, not the time interval.

An alternative method to calculate frequency is to measure the time between two consecutive occurrences of the event (the period T) and then compute the frequency f as the reciprocal of this time:

f = \frac{1}{T}.

A more accurate measurement can be obtained by taking many cycles into account and averaging the periods between each.

By stroboscope effect, or frequency beats

In case when the frequency is so high that counting is difficult or impossible with the available means, another method is used, based on a source (such as a laser, a tuning fork, or a waveform generator) of a known reference frequency f0, that must be tunable or very close to the measured frequency f. Both the observed frequency and the reference frequency are simultaneously produced, and frequency beats are observed at a much lower frequency Δf, which can be measured by counting. This is sometimes referred to as a stroboscope effect. The unknown frequency is then found from f=f_0\pm \Delta f.

Search results for Frequencies

Scanner Frequencies & Codes

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Short Wave and Ham Radio Frequencies and BandPlans

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Scanner frequencies, police, fire, NASCAR, airport, Ham radio.

Nationwide scanner frequency database, including police, fire, rescue, racing frequencies, airport, railroad, taxi, amateur radio, ham radio call signs... Up-to ...www.nationalradiodata.com/scanner-frequencies-frameset.html

SCANNER FREQUENCIES, Trunked Frequencies, Race Frequencies

Nationwide scanner frequencies database, including police, fire, rescue, racing frequencies, airport, railroad, amateur ham radio call signs.www.nationalradiodata.com/scanner-frequencies-home.jsp

Frequencies AtoZ - U

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News about Frequencies

Ryanair in USD140m Madrid expansion

Ireland Business WorldRyanair today announced that it will base two new aircraft valued at USD 140m in Madrid, open four new routes and double the frequencies on three existing routes - Dublin, Milan and Santander.http://www.businessworld.ie/livenews.htm?a=2299642;s=rolling...

Ambulances, Cop Cars Ready to Rumble

Wired NewsTaking a cue from annoying bass-heavy car stereos, emergency vehicles are using subwoofers to let people know they're comin' through. Wired.com http://blog.wired.com/cars/2008/10/motorists-in-ne.html

Stanislaus State University Gets Cash, New Computers

News10 SacramentoContract with Clearwire brings computers and cash to Stanislaus State Universityhttp://www.news10.net/news/local/story.aspx?storyid=48544

Rothschild wins technical bid to become spectrum auction agency

New KeralaNew Delhi, Oct 1 : The government has zeroed in on Mumbai-based NM Rothschild and Sons as the agency to conduct online auctions for allocating third generation radio frequencies in India, the government said.http://www.newkerala.com/topstory-fullnews-28303.html

Old violins reveal their secrets

NatureAcoustic measurements identify the signature of a Stradivarius.http://www.nature.com/news/2008/081002/full/news.2008.1147.h...

News about Frequencies

Virgin readies UK's first mobile TV broadcasts

ZDNet UKVirgin Mobile is on track to launch the UK's first true mobile broadcast TV service, a rebadged version of BT’s Movio product , this summer. Movio, which completed a successful trial earlier in the year, uses the same frequencies as DAB digital ... http://news.zdnet.co.uk/communications/0,1000000085,39278338...

Parents of dying newborns need clearer explanation of options

HULIQ.comThis qualitative study explored themes rather than frequencies and investigators did not report specific frequencies of responses as part of the study.http://www.huliq.com/11/68532/parents-dying-newborns-need-cl...

'Cognitive radios' to improve wireless devices

ITnews ... capable of learning in the process and of developing configurations that its designer never anticipated.” Adaptive, cognitive radios could enable techniques such as dynamic frequency sharing, in which radios automatically locate unused frequencies ... http://www.itnews.com.au/Tools/Print.aspx?CIID=122878

Sapphire to Release Watercooled, Overclocked Radeon HD 4870

SoftpediaIn addition, the water cooling solution appears to be the most reliable choice for achieving the impressive overclocked settings, as these GPUs tend to get fairly hot when they reach such frequencies.http://news.softpedia.com/news/Sapphire-to-Release-Watercool...

Xperia Phones May Not Use Windows

Redorbit.comHe said frequencies supported by the X1 -- which contains a Qualcomm chipset -- suggested it would likely be better suited to AT&T's networks than those of other U.S. carriers.http://www.redorbit.com/news/technology/1557112/xperia_phone...

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Frequencies of Musical Notes

Frequencies for equal-tempered scale This table created using A 4 = 440 Hz Speed of sound = 345 m/s = 1130 ft/s = 770 miles/hr ("Middle C" is C 4)http://www.phy.mtu.edu/~suits/notefreqs.html

Scanner Frequencies

Scanner frequencies for thousands of cities.http://www.cityfreq.com/

Channels and Frequencies | CBC Radio and Television

CBC Radio ... Find your channel and frequency. To view the stations and frequencies that are available for a specific location, please select your region from the list.http://www.cbc.ca/frequency/

NOAA Weather Radio

Nationwide Station Listing Using Broadcast Frequencies. 162.400 MHz : 162.425 MHz : 162.450 MHz : 162.475 MHz : 162.500 MHz : 162.525 MHzhttp://www.nws.noaa.gov/nwr/nwrbro.htm

Dreamtime Frequencies - Multimedia Sacred Art and Design Studio

Dreamtime Frequencies Home Inspired by the Ancient, Incorporated into the Present, A Vision for the Future,http://www.dreamtimefrequencies.com/
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Radio Frequencies May Keep You Look...

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Emergency Crews On Different Freque...

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Answers for Frequencies

hey2a

What other frequencies should I put in my police scanner?

hey2aCheck the FCC web site for frequencies at www.fcc.gov. It's free and it's public information. Nothing secret or anything like that. There are several ways to search the data base. Check for police...
Chris K

What frequencies would blow a subwoofer faster?

Chris KOn the contrary..the coils of a sub are cooled by movement. The less movement, the less they're cooled so high frequencies would be more damaging. The only parts that actually have any wear and tea...
kean_144

What the difference between screen frequencies?

kean_144Hertz refers to how fast your monitor can fill the pixels on the screen. 60 hertz it can fill the pixels 60 times a second. At 85 hertz it can fill 85 times per second. This way it keeps your scree...
klee3b

What are the lowest two frequencies that produce an interference maximum at the microphone's location?

klee3bd1 = 2.25 + 0.375 d2 = 2.25 - 0.375 d1 - d2 = 0.750 Vs ≈ 343.6 m/s @ 20°C V = f λ λ = 0.750/n, n = 1, 2, 3, 4, . . . . f ≈ 343.6n/0.750 f(1) ≈ 471 Hz f(2) ≈ 943 Hz
ScorpzDez

What are police scanner frequencies for Washington state northwest?

ScorpzDezHere ya go, pick the state and counties around you http://www.radioreference.com/apps/db/ If you want to dig deep, follow the links here you can use the FCC search tool, It's one of my answers...

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