Antenna Basics(Frequency Bands)

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How can your cell phone and your television work at the same time? Both use antennas to receive information from electromagnetic waves, so why isn’t there a problem?

The answer goes back to the fundamental secret of the universe. No matter what information you want to send, that waveform can be represented as the sum of a range of frequencies. By the use of modulation (which in a nutshell shifts the frequency range of the waveform to be sent to a higher frequency band), the waveforms can be relocated to separate frequency bands

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As an example, cell phones that use the PCS (Personal Communications Service) band have their signals shifted to 1850-1900 MHz. Television is broadcast primarily at 54-216 MHz. FM radio operates between 87.5-108 MHz.

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he set of all frequencies is referred to as “the spectrum”. Cell phone companies have to pay big money to get access to part of the spectrum. For instance, AT&T has to bid on a slice of the spectrum with the FCC, for the “right” to transmit information within that band. The transmission of EM energy is greatly regulated. When AT&T is sold a slice of the spectrum, they can not transmit energy at any other band (technically, the amount transmitted must be below some threshold in adjacent bands).

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The Bandwidth of a signal is the difference between the signals high and low frequencies. For instance, a signal transmitting between 40 and 50 MHz has a bandwidth of 10 MHz. This means that the energy of the signal is contained between 40 and 50 MHz (and the energy in any other frequency range is negligible).

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We’ll wrap up with a table of frequency bands along with the corresponding wavelengths. From the table, we see that VHF is in the range 30-300 MHz (30 Million-300 Million cycles per second). At the very least then, if someone says they need a “VHF antenna”, you should now understand that the antenna should transmit or receive electromagnetic waves that have a frequency of 30-300 MHz.

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Frequency Band Name Frequency Range Wavelength (Meters) Application
Extremely Low Frequency (ELF)
3-30 Hz
10,000-100,000 km
Underwater Communication
Super Low Frequency (SLF)
30-300 Hz
1,000-10,000 km
AC Power (though not a transmitted wave)
Ultra Low Frequency (ULF)
300-3000 Hz
100-1,000 km
Very Low Frequency (VLF)
3-30 kHz
10-100 km
Navigational Beacons
Low Frequency (LF)
30-300 kHz
1-10 km
AM Radio
Medium Frequency (MF)
300-3000 kHz
100-1,000 m
Aviation and AM Radio
High Frequency (HF)
3-30 MHz
10-100 m
Shortwave Radio
Very High Frequency (VHF)
30-300 MHz
1-10 m
FM Radio
Ultra High Frequency (UHF)
300-3000 MHz
10-100 cm
Television, Mobile Phones, GPS
Super High Frequency (SHF)
3-30 GHz
1-10 cm
Satellite Links, Wireless Communication
Extremely High Frequency (EHF)
30-300 GHz
1-10 mm
Astronomy, Remote Sensing
Visible Spectrum
400-790 THz (4*10^14-7.9*10^14)
380-750 nm (nanometers)
Human Eye

Table 1. Chart of Common Frequency Bands

 

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Basically the frequency bands each range over from the lowest frequency to 10 times the lowest frequency. Antenna engineers further divide the bands into things like “X-band” and “Ku-band”. That is the basics of frequency. To understand at a more advanced level move on to the next topic.