Orthogonal Transducer Mode

A Orthogonal Mode Transducer ( OMT or diplexor of polarization ), is a device belonging to a food of a parabolic Aerial and being used for combining or separating the two orthogonal signals in polarity LHCP and RHCP. The OMT belongs to emsemble ODU (Out-Door Unit), it agrees between LNB, BUC and the Feeder-Horn opposite the parabola of the equipment VSAT.

This device is used in the ground stations of the satellites VSAT with double polarization: “(VSAT Very Small Terminals Aperture)”, terminals with small opening, antennas of radar, radiometers, and connections. They are usually connected to the downconverter or LNB of the antenna and the HPA for an antenna of transmission.

In all the cases, there are two polarizations of the radio operator signals (horizontal and vertical), the transmitted radio signal and the received signal of the antenna would be “orthogonal”.

The orthogonal character of the signals wants to say that the two radio operator signals are perpendicular between them. The device of OMT is used to separate the two similar signals in frequency, a signal of high power and a signal of bottom grade.

The insulation is essential because the element of transmission can damage seriously if the very sensitive element of reception, if it is not protected with the junction from the antenna feeder.

The signal of transmission of the relatively high power (1, 2, or 5 Watts typically for the common equipment of VSAT) equipped with a Block Up Converter, “of rising converter of blocks” and of the received power very basic power of signal (µ-volts) comming of the antenna (air) to the unit of receiver of LNB, is in this relative case with 90°.

When the two (2) signals are with 90° between them, this configuration of transmission/reception is known like “Orthogonal Transducer Mode” (orthogonal sensor of mode) (OMT). In the band Ku, a case of the type of operation VSAT, a OMT Orthomode transducer provides an insulation of 40dB between each radio operator port connected to the feeder horn which is put opposite with the reflectors parabolic.

The parabolic feeder-horn of reflectors (on lefts in 1st photograph) of the antenna circular of is polartié so that the coupling of polartié horizontal and polarié vertical of the radio operator signals are carried out.

This insulation of 40dB ensures protection essential with the very sensitive amplifier of the receiver against the signal of the transmitter relatively strong in power. More insulation could be obtained by using a filter selective radio frequency to carry out an insulation of 100dB surroundings.

The image shows two types of the elements, OMT of Portenseigne, and Feed-Horn d' Hirschman, composing the Unit Out-door .

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