Wireless WaveNet Link AX, Инструкция по установке и эксплуатации

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WaveNet Link AX Installation and Operations Manual
2.5 Theory of Operation
General Overview
The Link AX is a point to point Wireless ATM-25 Extender operating in the 5.3/5.7 GHz U-NII
band as authorized in rule sections 15.401 through 15.407. The unit is enclosed in a weather
proof outdoor enclosure and is intended to provide data links over distances up to 15 km. The
radio in the unit operates full duplex, transmitting and receiving data at the rate of 8.192 Mbps.
The radio is modulated using BPSK.
Circuit Description
The following circuit description is intended to explain the operation of the radio at the block
diagram level. This text is written with the idea that the reader has the block diagram readily
available, as it will aid in understanding the signal flow in the radio.
2.5.1 Link AX Transmitter
The physical interface to the radio consists of ATM-25 cells that are routed to ATM physical
interface (PHY) chip. The PHY chip stores the data cells, and then converts them into a
synchronous 8.448 Mbps data stream that is fed into the transmitter. To mark cell boundries,
a SYNC byte (01111110) is inserted at the beginning of every cell. Zero insertion circuitry,
inserts a zero after five consecutive ones, guaranteeing SYNC byte uniqueness while
transmiting the cell’s content.
The data is differentially encoded and scrambled before it is routed through the transmit
baseband filter to provide spectral shaping. The baseband filter is a five pole low pass filter.
After amplification, the baseband signal is fed to the modulator consisting of a doubly
balanced mixer. The modulator is running directly at the transmitter frequency of 5.775 GHz
±
50 MHz. The local oscillator signal of the mixer is supplied from the frequency synthesizer
section, with the frequency dependant on the RF channel selected.
From the output of the modulator, the signal is amplified and then passed through a 150 MHz
wide bandpass filter to remove any local oscillator products from the output spectrum. After
filtering, the signal is passed through a series of amplifier and attenuator stages that are used
to control the output power level. With a combination of fixed and variable attenuation the
output power can be set to one of four different levels to accommodate different antennas
used with the product.
The power setting is maintained by an active ALC circuit that samples the transmitter output
power and then adjusts the variable attenuator to keep the output power constant over the
operating temperature of the unit. The power level is controlled to 1/-2 dB of the set
point.
Following the attenuators the signal is fed through additional amplification to bring the output
level to a maximum of +14 dBm at the output of power amplifier. A lowpass matching section
follows the power amplifier to aid in filtering harmonics of the signal. After passing through the
duplexer, the power level at the antenna port is a maximum of +12 dBm.