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Radio Frequency (RF) is the mode of communication for wireless technologies of all kinds, including cordless phones, radar, ham radio, GPS, and radio and television broadcasts. This technology is so much a part of our lives we scarcely notice it for its ubiquity. From baby monitors to cell phones, Bluetooth® to remote control toys, radio waves are all around us. These are electromagnetic waves which propagate at the speed of light, or 186,000 miles per second (300,000 km/s). The frequencies of RF waves, however, are slower than those of visible light, making them invisible to the human eye.
The frequency of a wave is determined by its oscillations or cycles per second. One cycle is one hertz (Hz); 1,000 cycles is 1 kilohertz (KHz); 1 million cycles is 1 megahertz (MHz); and 1 billion cycles is 1 gigahertz (GHz). A station on the AM dial at 980, for example, broadcasts using a signal that oscillates 980,000 times per second, or has a frequency of 980 KHz. A station a little further down the dial at 710 broadcasts using a signal that oscillates 710,000 times a second, or has a frequency of 710 KHz. With a slice of the pie licensed to each broadcaster, the RF range can be neatly divided and utilized by multiple parties.
Every device in the United States that uses RF waves must conform to the Federal Communications Commission's (FCC) regulations. A baby monitor, for example, must operate using the designated frequency of 49 MHz. Cordless phones and other devices have their own designated frequencies.
The FCC shares responsibility for RF assignment with the National Telecommunications and Information Administration (NTIA), which is responsible for regulating federal uses of the radio spectrum. At present, according to the FCC, frequencies from 9 KHz to 275 GHz have been allocated, with the highest bands reserved for satellite and radio astronomy. The sample chart below lists some of the major categories with approximate ranges. In actuality, there are no gaps between categories, as hundreds of other uses are also assigned, from garage door openers and alarm systems to amateur radio and emergency broadcasting.
|Aeronautical/Maritime||9 KHz - 535 KHz|
|AM radio||535 KHz - 1,700 KHz|
|Shortwave radio||5.9 MHz - 26.9 MHz|
|Citizen's Band (CB)||26.96 MHz - 27.41 MHz|
|TV stations 2-6||54 MHz - 88 MHz|
|FM radio||88 MHz - 108 MHz|
|TV stations 7-13||174 MHz - 220 MHz|
|Cell phones CDMA||824 MHz - 849 MHz|
|Cell phones GSM||869 MHz - 894 MHz|
|Air Traffic Control||960 MHz - 1,215 MHz|
|GPS||1,227 MHz - 1,575 MHz|
|Cell phones PCS||1,850 MHz - 1,990 MHz|
The RF table is divided and labeled according to frequency, with Extremely Low Frequency (ELF) occupying one end at just 3-30 Hz, and Extremely High Frequency (EHF) at the other, representing 30-300 GHz. The bands most of us are familiar with are Very High Frequency (VHF), used by radio and television stations 2-13, and Ultra High Frequency (UHF), used by other television stations, mobile phones and two-way radios. Microwave ovens even use RF waves to cook food, but these waves are in the Super High Frequency band or SHF. Following the electromagnetic spectrum into even higher frequencies, one finds infrared waves, and finally visible light.
The exact range of RF waves? That's a good question. It cannot be answered accurately. Even with computer models. Estimates are all that can be had.
Variables that must be considered include (no, this isn't all of them, just the most important ones):
1.Amount of power generated by the transmitter.
2.Loss between the transmitter and the antenna.
3.Directivity of the antenna relative to the receiver.
4.Path loss / interference
5.Receiver antenna directivity
6.Loss between the receiver and the antenna
7.Sensitivity and bandwidth of the receiver.
That's the basics for any path, and moving the transmitter or receiver any at all in any direction changes the value for four of these variables.
Things, that is anything, moving around inside the path alters #4.
I have almost 30 years experience in RF, and I'd like to know the exact range of RF waves, too. Of course, I've also learned there is no absolute answer. Even the frequency of the transmitter must be considered.
Drift speed tells you how fast a particular electron is expected to travel down a wire. When that electron moves closer to the load, like a light bulb, it bumps other electrons between it and the load. While it may take a second for that electron to drift down range, the electromotive force is felt immediately.
Drift is a function of Average Wire Gauge. Electromotive force is not. You can get voltage and still not have enough current.
the average "drift speed" of electrons inside a conductor is barely 1mm/s.....but, when you switch on an appliance, for example a bulb, it glows even before you could blink? please explain.
I would like to know the exact range of the rf waves?
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