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10GHz - 10/100
Mbit Full Duplex DataLink
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I'm starting a new project about microwave data link radio for digital communication at 10GHz. The idea is to build high-speed full duplex bridge for Ethernet UTP 10/100Mbit interface. Module is based on 10GHz Point-to-Point Gunnplexer Communications principle. It uses independent parabolic antennas with tubular waveguide for the feedforn or rectangular feedhorn for the offset reflector antennas.
The link as described uses two prepackaged microwave transceiver modules, called "Gunnplexers." These modules are remarkably simple and reliable. They consist of three diodes, a resonant cavity, and an antenna aperture. One of the diodes, the "Gunn diode," generates RF energy at 10 GHz. Another, the "varactor diode," is used to vary the exact frequency of the emitted microwaves in accordance with the Ethernet signal to be transmitted. Finally, the third diode, known as the "mixer," is responsible for receiving the signal from the Gunnplexer at the other end of the link. Because it's impractical to carry out the necessary Ethernet signal-recovery operations at the Gunnplexer's native frequency of 10 GHz, the mixer diode actually delivers the recovered signal at an "intermediate frequency," or IF, at a more reasonable frequency of 118 MHz.
Where, exactly, does this 118 MHz intermediate frequency come from? It turns out that the mixer diode can mix, or heterodyne, the transmitted signal from the Gunn diode in its own Gunnplexer with the signal received from the distant end, to yield the desired IF frequency. All that is necessary is to tune the two Gunnplexers to frequencies which are 118 MHz apart. In our case, we arbitrarily designate one Gunnplexer for operation at 10.172 GHz, with its counterpart tuned 118 MHz higher at 10.290 GHz. The exact frequencies are not important (and are, in any event, almost impossible to measure precisely without microwave test equipment), as long as one Gunnplexer is tuned 118 MHz below its counterpart at the other end of the link. This heterodyne effect is essentially available for free as a consequence of the design of the Gunnplexer transceivers, and it saves us a great deal of trouble in the design and construction of the rest of the link's circuitry.
But there are also a couple of key drawbacks to this simple idea. One is that there is no easy way to allow more than two Gunnplexers to communicate with each other. The use of three or more Gunnplexers in a multipoint network topology would be mathematically impossible, since there is no way that three or more signal sources can all be 118 MHz apart from one another! Consequently, the design as presented here is useful only for connecting two machines or subnetworks.
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