Radio frequency - Wikipedia
The difference between 93 MHz and 94 MHz will be irrelevant in a practical Signal strength and frequency (or wavelength--they are the same. The wavelength and frequency of light are closely related. The higher the frequency, the shorter the wavelength. Because all light waves move through a. Radio Frequency (RF) and wireless have been around for over a Table 1 shows a relationship between frequency (f) and wavelength (λ).
The receiver first uses a bandpass filter to separate the desired radio station's radio signal from all 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 microprocessorwhich interacts with 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 frequencymeasured in kilohertz kHzmegahertz MHz or gigahertz GHz.
The bandpass filter in the receiver consists of a tuned circuit which acts like a resonatorsimilarly to a tuning fork. The resonant frequency is set equal to the frequency of the desired radio station.
Frequency Vs Wavelength
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 the tuned circuit and not passed on. Biological and environmental effects[ edit ] Radio waves are nonionizing radiationwhich means they do not have enough energy to separate electrons from atoms or moleculesionizing them, or break chemical bondscausing 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 a space heater or wood fire.
- Radio wave
- Introduction to RF & Wireless Communications Systems
- Radio frequency
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. However, unlike infrared waves, which are mainly absorbed at 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.Traveling Waves: Crash Course Physics #17
For example, the 2. Radio waves have been applied to the body for 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 treatment, to kill cancer cells. 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.
One can speak of an electromagnetic fieldand these units are used to provide information about 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.
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 the far field zone. The relationship between these units is like this: The term "wavelength" is left over from the early days of radio. Back then, frequencies were measured in terms of the distance between the peaks of two consecutive cycles of a radio wave instead of the number of cycles per second.
Even though radio waves are invisible, there is a measurable distance between the cycles of electromagnetic fields making up a radio wave. The distance between the peaks of two consecutive cycles is measured in meters.
The relationship between a radio signal's frequency and its wavelength can be found by the following formula: Thus, kHz, 9.
As the formula indicates, the wavelength of a radio signal decreases as its frequency increases. Back to Top 2. RF itself has become synonymous with wireless and high-frequency signals, describing anything from AM radio between kHz and kHz to computer local area networks LANs at 2.
If one considers microwave frequencies as RF, this range extends to GHz. The following two tables outline the various nomenclatures for the frequency bands. The third table outlines some of the applications at each of the various frequency bands.
How are frequency and wavelength related?
A wave or sinusoid can be completely described by either its frequency or its wavelength. They are inversely proportional to each other and related to the speed of light through a particular medium.
The relationship in a vacuum is shown in the following equation: As frequency increases, wavelength decreases. For reference, a 1 GHz wave has a wavelength of roughly 1 foot, and a MHz wave has a wavelength of roughly 10 feet. Microwave Letter Band Designations Table 3: Frequency Applications and Allocations in the U. RF measurement methodology can generally be divided into three major categories: Spectrum analyzers, which provide basic measurement capabilities, are the most popular type of RF instrument in many general-purpose applications.