Passive radio relay
A passive directional radio redirection is a system for realizing a directional radio link which, due to an obstacle in the signal path, is not possible in a direct way as with a line of sight . It is particularly suitable for high frequencies of the UHF and the SHF band.
Technical background
Compared to the establishment of a relay station with active components, the passive directional radio redirection has the advantage that no power supply is required at the place of its installation and no further frequencies are required. Relay stations with active components usually require different transmission and reception frequencies, as there is a risk of feedback when using the same frequency . On the other hand, there is the disadvantage that with passive directional radio diversion the diverted signal is often considerably weaker. As a rule, a passive directional radio redirection works equally well in both directions.
There are two methods of passive diversion:
The antenna method
The signal from a directional antenna with the greatest possible gain z. B. caught a parabolic antenna and fed via a coaxial cable or waveguide to a second directional antenna, which radiates it in the desired direction.
Such systems are occasionally used as television converters or as tunnel transmitters .
The reflector method (deflection mirror)
Flat surfaces made of metallic material are used for deflection, which are arranged in such a way that the incident signal is directed in the desired direction according to the law of reflection . Cavity prisms can also be used for small deflection angles . Mountains and metallic building facades can also act as reflectors.