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File:Seattle-Capitol-Hill-Radio-Antennas-3357.jpg

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English: Antennas on the roof of a telephone switching center near Madison St. and 17th Ave, Capitol Hill, Seattle, Washington state, USA.
This is part of the TD-2 AT&T Long Lines system, a microwave relay network created by AT&T in the 1950s to relay telephone calls and other data between cities in the USA. The four angular cone-shaped antennas are called Hogg or horn-reflector antennas, invented by Albert Beck and Harald Friis in 1941 and developed by D. L. Hogg at Bell Labs in 1961. They operate at C-band frequencies. at 4 and 6 GHz. They consist of a vertical flaring metal horn with a reflector mounted in the mouth at a 45° angle, so the beam of microwaves is emitted horizontally. The reflector is a segment of a parabolic reflector, so the antenna is equivalent to a parabolic antenna fed off-axis. The advantage of this type of antenna over an ordinary parabolic (dish) antenna is that it radiates very little energy outside of the main beam. This allows the same microwave frequencies to be used by several nearby antennas pointing in different directions without interfering with each other. These KD-15676 antennas have a gain of about 43 dBi and produce a beamwidth (HPBW) of about 1° at 6 GHz. (From KD-15676 Horn Reflector Antenna Description, Bell System standards, AT&T)
Microwave links like these use a pair of antennas (one transmitting and one receiving) to send a beam of microwaves of a few watts power to a similar station about 30 miles away. Each antenna can carry tens of thousands of telephone calls. Several round parabolic dish antennas are also visible.
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Source Self-photographed
Author Vladimir Menkov
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Derivative works of this file:  Hogg horn antennas.jpg


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current00:54, 21 April 2007Thumbnail for version as of 00:54, 21 April 20072,048 × 1,536 (1.12 MB)Vmenkov (talk | contribs) ==Summary== {{Information |Description={{en|A radio station (?) near Madison St and 17th Ave, Capitol Hill, Seattle}} |Source=Own photo |Date=2007-Mar-10 |Author=Vladimir Menkov |Permission={{self2|GFDL|cc-by-sa-2.5,2.0,1.0}} }} [[Cat

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