Antennas are used to send and receive frequency signals. Very high frequency (VHF) and ultrahigh frequency (UHF) antennas are designed to transmit and pick up different ranges of frequencies in the broadcast spectrum. To help simplify matters, the frequencies in the broadcast spectrum are grouped into channels. Each channel contains six frequencies. For example, channel 2 is assigned to the 54 to 60 megahertz range; channel 3 is assigned to the 60 to 66 megahertz range; and so on. VHF antennas do not transmit and receive the same channels as UHF antennas.
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Look at the size of the elements that make up the antenna. VHF signals are on the low side of the broadcast frequency band, which means they have longer wavelengths. In order to pick up these longer wavelengths of VHF signals, the elements that make up a VHF antenna have to be sufficiently long as well. UHF signals, on the other hand, have shorter wavelengths. The component parts of a UHF antenna do not have to be as long as those used on VHF antennas. Therefore, UHF antennas are comparatively smaller than VHF antennas.
Look at the shape of the antenna. The most common configuration for VHF antennas is the "rabbit ears" design. Common configurations for UHF antennas include the bowtie, the ring or loop, and a whole host of other shapes. Because the components that make up this antenna are smaller in size, UHF antennas can be designed in more complex configurations than VHF antennas. Some UHF antennas are patterned after fractal designs.
Examine your television reception. VHF antennas can receive only RF channels 2 through 13. UHF antennas can receive RF channels 14 through 83. The RF channel of a broadcast station is not the same thing as the virtual station you tune into on your television set. RF, which stands for "radio frequency," it is the actual frequency channel that a communication's station is licensed to broadcast on. So while you might be tuned into channel 2 on your television set to watch your PBS shows, the RF channel of this PBS station may actually be 19. To find out what the true RF channels are for the TV stations in your broadcast zone, go to the "Choose an antenna" page on the AntennaWeb website (see Resources for link). Enter your address (or at least your ZIP code), and submit the form. Is your antenna incapable of receiving the TV stations broadcasting on the 2 through 13 RF channels? If so, you have a UHF antenna. Is your antenna incapable of picking up TV stations broadcasting on the 14 and up RF channels? If so, you have a VHF antenna. If your antenna picks up the entire spectrum of RF channels it's a combination VHF/UHF antenna.