trunk microwave equipment

Trunk Microwave Equipment

High cost, large transmission capacity, more stable performance, applicable to long haul and trunk

transmission

RF, IF, signal processing, and MUX/DEMUX units are all indoor. Only the antenna system is outdoor.

All Outdoor Microwave Equipment

• All the units are outdoor.

• Installation is easy.

• The equipment room can be saved.

Split-Mount Microwave Equipment (1)

The RF unit is an outdoor unit (ODU). The IF, signal processing, and MUX/DEMUX units are integrated in the indoor

unit (IDU). The ODU and IDU areconnected through an IF cable.

The ODU can either be directly mounted onto the antenna or connected to the antenna through a short soft

waveguide. Although the capacity is smaller than the trunk, due to the easy installation and maintenance, fast

network construction, it's the most widely used microwave equipment.

Split-Mount Microwave Equipment (2)

Unit Functions

o Antenna: Focuses the RF signals transmitted by ODUs and increases the signal gain.

o ODU: RF processing, conversion of IF/RF signals.

o IF cable: Transmitting of IF signal, management signal and power supply of ODU.

o IDU: Performs access, dispatch, multiplex/demultiplex, and modulation/demodulation for services.

Split-Mount Microwave Equipment – Installation

Microwave Antenna (1)

Antennas are used to send and receive microwave signals.

Parabolic antennas and cassegrainian antennas are two common types of microwave antennas.

Microwave antenna diameters includes: 0.3m, 0.6m, 1.2m, 1.8m,2.0m, 2.4m, 3.0m, 3.2metc.

Microwave Antenna (2)

Different frequency channels in same frequency band can share one antenna.

Antenna Adjustment (1)


During antenna adjustment, change the direction vertically

or horizontally. Meanwhile, use a multimeter to test the

RSSI at the receiving end. Usually, the voltage wave will be

displayed as shown in the lower right corner. The peak point

of the voltage wave indicates the main lobe position in the

vertical or horizontal direction. Large-scope adjustment is

unnecessary. Perform fine adjustment on the antenna to the

peak voltage point.

When antennas are poorly aligned, a small voltage may be

detected in one direction. In this case, perform coarse

adjustment on the antennas at both ends, so that the

antennas are roughly aligned.

The antennas at both ends that are well aligned face a little

bit upward. Though 1–2 dB is lost, reflection interference will

be avoided.


During antenna adjustment, the two wrong adjustment cases are show here. One antenna is aligned to another

antenna through the side lobe. As a result, the RSSI cannot meet the requirements.

Split-Mount Microwave Equipment – Antenna (1)

Antenna gain

Definition: Ratio of the input power of an isotropic antenna Pio to the input power of a parabolic antenna Pi when

the electric field at a point is the same for the isotropic antenna and the parabolic antenna.

‡ Calculating formula of antenna gain:

G = Pio/Pi = (πD/λ)2 * η

Half-power angle

Usually, the given antenna specifications contain the gain in the largest radiation (main lobe) direction, denoted by

dBi. The half-power point, or the –3 dB point is the point which is deviated from the central line of the main lobe

and where the power is decreased by half. The angle between the two half-power points is called the half-power

angle.

‡

Calculating formula of half-power angle:

θ0.5 = (65o ~ 70o) λ/D

Split-Mount Microwave Equipment – Antenna (2)

Cross polarization discrimination

Suppression ratio of the antenna receiving heteropolarizing waves, usually, larger than 30 dB.

‡ XdB＝10lgPo/Px

‡ Po: Receiving power of normal polarized wave

‡ Px: Receiving power of abnormal polarized wave

Antenna protection ratio

‡ Attenuation degree of the receiving capability in a direction of an antenna compared with that in the main lobe

direction. An antenna protection ratio of 180° is called front-to-back ratio.

Split-Mount Microwave Equipment –ODU (1)


Specifications of Transmitter

o Working frequency band

Generally, trunk radios use 6, 7, and 8 GHz frequency bands. 11, 13 GHz and

higher frequency bands are used in the access layer (e.g. BTS access).

o Output power

The power at the output port of a transmitter. Generally, the output power is 15 to 30 dBm.


Local frequency stability

If the working frequency of the transmitter is unstable, the demodulated effectived signal ratio will be

decreased and the bit error ratio will be increased. The value range of the local frequency stability is 3 to 10

ppm.

Transmit Frequency Spectrum Frame

The frequency spectrum of the transmitted signal must meet specified requirements, to avoid occupying too

much bandwidth and thus causing too much interference to adjacent channels. The limitations to frequency

spectrum iscalled transmit frequency spectrum frame.


Specifications of Receiver

o Working frequency band

Receivers work together with transmitters. The receiving frequency on the local station is the transmitting

frequency of the same channel on the opposite station.

o Local frequency stability

The same as that of transmitters: 3 to 10 ppm

o Noise figure

The noise figure of digital microwave receivers is 2.5 dB to 5 dB.


‡ Passband

To effectively suppress interference and achieve the best transmission quality, the passband and amplitude

frequency characteristics should be properly chosen. The receiver passband characteristics depend on the IF

filter.

Selectivity

Ability of receivers of suppressing the various interferences outside the passband, especially the interference

from adjacent channels, image interference and the interference between transmitted and received signals.

‡ Automatic gain control (AGC) range

Automatic control of receiver gain. With this function, input RF signals change within a certain range and the

IF signal level remains unchanges.


Split-Mount Microwave Equipment –IDU

trunk microwave equipment

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