A passive repeater or passive radio link deflection, is a reflective or sometimes refractive panel or other object that assists in closing a radio or

microwave link Microwave transmission is the transmission of information by electromagnetic waves with wavelengths in the microwave frequency range of 300MHz to 300GHz(1 m - 1 mm wavelength) of the electromagnetic spectrum. Microwave signals are normally lim ...

, in places where an obstacle in the signal path blocks any direct, line of sight communication. Compared to a

microwave radio relay Microwave transmission is the transmission of information by electromagnetic waves with wavelengths in the microwave frequency range of 300MHz to 300GHz(1 m - 1 mm wavelength) of the electromagnetic spectrum. Microwave signals are normally lim ...

station with active components, a passive repeater is far simpler and needs little maintenance and no on-site electric power. It also does not require additional frequencies, unlike active repeater stations which use different transmit and receive frequencies to prevent feedback. The corresponding disadvantage is that without amplification the returned signal is significantly weaker, although in some configurations they can actually provide gain of 100 to 130 dB for u.h.f. and microwave radio-relay stations. Passive radio relay link deflection systems in the vertical level can be realized by receiving the signal with a

parabolic antenna A parabolic antenna is an antenna that uses a parabolic reflector, a curved surface with the cross-sectional shape of a parabola, to direct the radio waves. The most common form is shaped like a dish and is popularly called a dish antenna or pa ...

and leading it through a waveguide to a second parabolic antenna, where it is radiated. For passive

link deflections in the horizontal plane, flat surfaces of metallic material are used, arranged so that the angle of incoming beam corresponds to the angle of the outcoming signal. The resulting structure resembles a

billboard A billboard (also called a hoarding in the UK and many other parts of the world) is a large outdoor advertising structure (a billing board), typically found in high-traffic areas such as alongside busy roads. Billboards present large advertise ...

.Radio Mirrors for Communications, May 1969 Electronics World
/ref> Similar systems are used also occasionally for

TV relay transmitter A broadcast relay station, also known as a satellite station, relay transmitter, broadcast translator (U.S.), re-broadcaster (Canada), repeater (two-way radio) or complementary station (Mexico), is a broadcast transmitter which repeats (or tran ...

s or as tunnel transmitters. In these cases, a Yagi antenna receives the transmitted signal and supplies it by way of a

coaxial cable Coaxial cable, or coax (pronounced ) is a type of electrical cable consisting of an inner conductor surrounded by a concentric conducting shield, with the two separated by a dielectric ( insulating material); many coaxial cables also have a p ...

to a second Yagi antenna.

Photos of microwave repeaters

See also external links for photos of variety of other passive repeaters. File:Microwave_repeaters_Black_Hill_Hong_Kong.png, Microwave repeaters on Black Hill, Hong Kong File:Black Hill Hong Kong microwave repeater.jpg, Closer view of one of the Microwave repeaters on Black Hill, Hong Kong File:無給電中継装置.jpg, Microwave repeater on a hill in Nagano, Japan

External links

Radio Mirrors for Communications, May 1969 Electronics World

Passive Repeater Engineering, Microflect, Co. Inc, 1989

References

{{Reflist Telecommunications infrastructure it: Ripetitore