Television antenna
Indoor antennas are designed to be located on top of or next to the television set, but are ideally placed near a window in a room and as high up as possible for the best reception.
[5] The antenna is connected to the television with a specialized cable designed to carry radio current, called transmission line.
Radio waves in these bands travel by line-of-sight; they are blocked by hills and the visual horizon, limiting a television station's reception area to 65–95 km (40–60 miles), depending on terrain.
It is difficult to design a single antenna to receive such a wide wavelength range, and there is an octave gap from 216 to 470 MHz between the VHF and UHF frequencies.
[11] In East Germany, the areas that could not receive western TV signals were referred to as the Tal der Ahnungslosen, or Valley of the Clueless.
[6] They are often perfectly adequate in urban and suburban areas, which are usually within the strong radiation footprint of local television stations.
It is constructed of two telescoping rods attached to a base, which extend out to about 1 m (3.3 feet) length (approximately one-quarter wavelength at 54 MHz) and can be collapsed when not in use.
The measured gain of rabbit ears is low, about ―2 dBi, or ―4 dB with respect to a half wave dipole.
Still, its wide-angle reception pattern may allow it to receive several stations located in different directions without requiring readjustment when the channel is changed.
Another reason for the V shape is that when receiving channels at the top of the band with the rods fully extended, the antenna elements will typically resonate at their 3rd harmonic.
[6] This consists of a single telescoping rod about a meter (3.3 feet) long attached to the television, which can be retracted when not in use.
This of course also depends by country and region: for example in the UK and Ireland, terrestrial TV broadcasts are only on the UHF band, meaning that a loop antenna is necessary and the rabbit ears would only be useful for FM radio reception.
[15] Internally, the thin, flat square is a loop antenna with its circular metallic wiring embedded into conductive plastic.
As an antenna design provides higher gain (compared to a dipole), the main lobe of the radiation pattern becomes narrower.
[17] These are composed of multiple half-wave dipole elements, consisting of metal rods approximately half of the wavelength of the television signal, mounted in a line on a support boom.
Another design used mainly for UHF reception is the reflective array antenna, consisting of a vertical metal screen with multiple dipole elements mounted in front of it.
More extended elements that pick up VHF frequencies are located at the back of the boom and often function as a log-periodic antenna.
Shorter elements that receive the UHF stations are located at the front of the boom and often function as a Yagi antenna.
In a given region, it is sometimes arranged that all television transmitters are located in roughly the same direction and use frequencies spaced closely enough that a single antenna suffices for all.
There are also varying local ordinances which restrict and limit such things as the height of a structure without obtaining permits.
Putting an antenna indoors significantly decreases its performance due to lower elevation above ground level and intervening walls; however, in strong signal areas, reception may be satisfactory.
To prevent the antennas from interfering with each other, the vertical spacing between the booms must be at least half the wavelength of the lowest frequency to be received (Distance = λ/2).
It is also important that the cables connecting the antennas to the signal splitter/merger be precisely the same length to prevent phasing issues, which cause ghosting with analog reception.
For side-by-side placement of multiple antennas, as is common in a space of limited height such as an attic, they should be separated by at least one full wavelength of the lowest frequency to be received at their closest point.
