In microwave radio systems, frequency modulation (FM) is used rather than amplitude modulation (AM), this is explained because amplitude modulated signals are more sensitive to amplitude nonlinearities that are also inherent to broadband microwave amplifiers. On the other hand, signals emitted in modulated frequency are relatively more robust to this type of nonlinear distortion, and can be transmitted by amplifiers that have compression or amplitude nonlinearity, with relatively little demerit. Also, FM signals are less sensitive to random noise and can propagate with lower transmission powers.

Intermodulation noise is an essential factor in the design of FM radio systems. In AM systems, this noise is caused by amplitude nonlinearity in the repeater. In FM systems, intermodulation noise is mainly caused by transmission gain and delay distortion. Consequently, in FM systems it is a function of the amplitude "Amplitude (physical)") of the signal and the magnitude of the frequency deviation. Thus the characteristics of frequency modulated signals are more suitable for microwave transmission than amplitude modulated signals.

Contenido

Los sistemas de radio por microondas que usan modulación de frecuencia se conocen ampliamente por proporcionar comunicaciones flexibles, confiables y económicas, de punto a punto, cuando usan la atmósfera terrestre como medio de transmisión. Los sistemas de microondas FM que se usan con el equipo multiplexor adecuado son capaces de conducir en forma simultánea desde unos pocos circuitos de voz de banda angosta, hasta miles de circuitos de voz de alta velocidad, audio de calidad comercial y televisión comercial. Los estudios comparativos de costo han demostrado que los sistemas radio por microondas con modulación por frecuencia (FM) es, casi siempre, el método más económico de proporcionar circuitos de comunicaciones cuando no hay ya cables metálicos ni fibras ópticas, o cuando existen duras condiciones de terreno o de clima. También, los sistemas de microondas FM se pueden ampliar con facilidad.

En la figura se ve un diagrama de bloques simplificado de un sistema de microondas de FM. La banda base es la señal compuesta que modula la portadora FM, y que puede abarcar uno o más de los sistemas siguientes.

1. Canal de banda de voz multiplexado por división de frecuencia.

2. Canales de banda de voz multiplexados por división de tiempo.

3. Vídeo compuesto de calidad comercial o teléfono visual.

4. Datos en banda ancha.

5. Ancho de Banda en Fibra Óptica 4,5 MHz.

FM Microwave Radio Transmitter

In the FM microwave transmission shown in the transmitter block diagram, a pre-amplification (pre-emphasis) stage precedes the frequency modulator (FM shifter). This pre-amplification increases the amplitude of the upper baseband signals. Allowing the lower baseband frequencies to modulate the frequency of the IF carrier, and the upper baseband frequency to modulate the phase of that carrier. This block diagram ensures a more uniform signal-to-noise ratio across the entire baseband spectrum. The FM diverter stage delivers the modulation of the IF carrier which at the end becomes the main microwave carrier, normally the typical intermediate frequencies are between 60 and 80 MHz, where 70MHz is most suitable. Low index frequency modulation is used in the FM diverter. Where the modulation indices are kept between 0.5 and 1, in this way a narrowband FM signal is realized at the output of the diverter, consequently the bandwidth of the F1 resembles that of common AM and approaches twice the maximum frequency of the baseband.

The F1 and its associated sidebands are converted to the higher frequencies of the microwave region, using the mixer, microwave oscillator and bandpass filter. To transfer the F1 to the RF stage, mixing and not multiplication is used because the modulation index does not change due to the heterodyning process. Also by multiplying the carrier of F1 the frequency deviation and the modulation index would be multiplied, thus increasing the bandwidth.

Microwave generators consist of a crystal oscillator followed by a series of frequency multipliers. For example a 125 MHz crystal oscillator followed by a series of multipliers, with combined multiplication factor equal to 48, could be used for a microwave carrier frequency of 6 GHz. The channel combining network provides a means of connecting more than one microwave transmitter from a single transmission line feeding the antenna.

FM microwave radio receiver

Receiver Block Diagram: The FM microwave radio receiver is shown, where the channel separator network block provides the isolation and filtering necessary to separate individual microwave channels and direct them to their respective receivers. The bandpass filter, AM mixer and microwave oscillator lower the frequencies from microwave RF to F1, and pass them to the FM demodulator. Where this demodulator is a conventional, non-coherent FM detector. At the output of the FM detector, a de-emphasis network restores the baseband signal to its original amplitude versus frequency characteristics.

Los radios de microondas emiten señales usando como medio la atmósfera terrestre, entre transmisores y receptores, para una mejor emisión y recepción, estos se encuentran en la cima de torres a distancias de 15 a 30 millas. Así los sistemas de radio de microondas tienen la ventaja obvia de contar con capacidad de llevar miles de canales individuales de información entre dos puntos, dejando a un lado la necesidad de instalaciones físicas, tales como los cables coaxiales o fibras ópticas. Así claro esta, se evita la necesidad de adquirir derechos de vías a través de propiedades privadas, además las ondas de radio se adaptan mejor para salvar grandes extensiones de agua, montañas altas o terrenos muy boscosos que constituyes formidables obstáculos para los sistemas de cable.

Entre las ventajas de radio de microondas están las siguientes:.

Radio link

A terrestrial radio link or terrestrial microwave provides connectivity between two sites (earth stations) in line-of-sight (LOS*) using radio equipment with carrier frequencies above 1 GHz. The emitted waveform can be analog (conventionally frequency modulated) or digital.

Microwaves are electromagnetic waves whose frequencies are within the super high frequency spectrum, SHF.

It is also usually offered by WiMAX installers to offer service from places where there is coverage to those nearby where there is not.

Microwave generators are critical generators in terms of operating voltage and current.

One of the means is not to act on the generator or amplifier but to use a pin diode device in the output guide, directly modulating the amplitude of the wave.

Another means is to use a ferrite phase shifter and modulate the wave in phase. In this case it is easy to obtain frequency modulation through the following process:

In a first stage, a low frequency carrier, for example 70 MHz, is FM modulated.

In a second stage, this modulated carrier is mixed with the main carrier at GHz frequency, for example 10 GHz.

A frequency filter passes the sum frequency, 10070 MHz with its 3 MHz side bands and therefore the passband will be from 10067 to 10073 MHz, which is the final microwave signal.

In the receiver, this signal is mixed with the 10 GHz local oscillator followed by a filter that takes advantage of the 70 MHz difference frequency, which is amplified and then detected by the usual FM techniques.

The main frequencies used in microwaves are around 12 GHz, 18 and 23 GHz, which are capable of connecting two locations between 1 and 25 kilometers away from each other. Microwave equipment operating between 2 and 6 GHz can transmit over distances between 30 and 50 kilometers.

Teams.

A radio link is made up of terminal equipment and intermediate repeaters. The function of repeaters is to overcome the lack of visibility imposed by the earth's curvature and thus achieve links higher than the optical horizon. The distance between repeaters is called hop.

The repeaters can be:

The antenna generally used in microwave radio links are of the parabolic type. The typical size is a diameter of about 3 meters. The antenna is rigidly fixed, and transmits a narrow beam that must be perfectly focused towards the receiving antenna.

These microwave antennas must be located at a considerable height above ground level, in order to achieve the greatest possible separations between them and be able to overcome possible obstacles. Without intermediate obstacles, the maximum distance between antennas is approximately 150 km. With repeater antennas, it is clear that this distance can be extended if the curvature of the earth is used, through which microwaves are deflected or refracted in the earth's atmosphere.

For example, two microwave antennas located at a height of 100 m can be separated by a total distance of 82 km, this occurs under certain conditions, such as terrain and topography. That is why this distance can vary according to the conditions handled.

The distance covered by microwave links can be increased by the use of repeaters, which amplify and redirect the signal. It is important to note that signal obstacles can be overcome through passive reflectors.

The transmitted microwave signal is distorted and attenuated as it travels from the transmitter to the receiver; these attenuations and distortions are caused by distance-dependent power loss, reflection and refraction due to obstacles and reflecting surfaces, and atmospheric losses.

Parabolic reflector: It is constructed of fiberglass or aluminum. The fiberglass case is constructed with a laminate reinforced with polyester resin; The surface is metallized with zinc.

Efficiency: in an antenna the gain is reduced for the following reasons:

Climate and terrain are the biggest factors to consider before installing a microwave system.

In summary, in a radio link there are losses due to:

The main use of this type of transmission is in long-distance telecommunications, it is presented as an alternative to coaxial cable or fiber optics.

This system requires fewer repeaters or amplifiers than coaxial cable but requires the antennas to be aligned.

The main uses of terrestrial microwaves are for television and voice transmission.

Microwave links are often used to link different buildings, where cable installation would be problematic or more expensive. However, because terrestrial microwave equipment typically uses licensed frequencies, additional economic and financial limitations are imposed by the licensing organizations or governments.

The main applications of a terrestrial microwave system are the following:

Terrestrial microwaves continue to be a very effective means of communication for metropolitan networks to interconnect banks, markets, department stores and cellular radio bases.

Likewise, radio links can be used to extend Internet coverage, as happens in places where WiMAX did not reach.[2]​.

Before fiber optics, these microwaves formed the heart of the long-distance telephone transmission system for decades.

Microwaves are also relatively cheap. Choosing two simple towers and putting antennas on each can cost less than burying 50 km of fiber through a congested urban area over a mountain, and can also be cheaper than renting fiber from a company that offers telephone service.

The microwave network equipment manufacturers are:[3]​

-Nokia

-NEC

-Ericsson

-Marelli

• Marconi

• GT&E")

• G.E.

• Philips

-Rohde & Schwartz")

-Kuhne")

-Codan")

-Alcatel

• Fujitsu

-Siemens

-ATI

-Hughes

• Ceragon")

-Saf Tehnika")

-Huawei

-ZTE.

The vast majority of current microwave radio systems are frequency modulation, which is analog in nature. However, recently new systems have been developed that use phase-switched modulation, or quadrature amplitude modulation, which are basically forms of digital modulation. There is also talk of satellite systems that use PCM or PSK, these two systems are similar to terrestrial microwave radio systems, without a doubt the two systems share many frequencies. The main difference between satellite and terrestrial radio systems is that satellite systems propagate signals outside the Earth's atmosphere, so they are capable of carrying signals much further away, using fewer transmitters and receivers.

In microwave radio systems, frequency modulation (FM) is used rather than amplitude modulation (AM), this is explained because amplitude modulated signals are more sensitive to amplitude nonlinearities that are also inherent to broadband microwave amplifiers. On the other hand, signals emitted in modulated frequency are relatively more robust to this type of nonlinear distortion, and can be transmitted by amplifiers that have compression or amplitude nonlinearity, with relatively little demerit. Also, FM signals are less sensitive to random noise and can propagate with lower transmission powers.

Intermodulation noise is an essential factor in the design of FM radio systems. In AM systems, this noise is caused by amplitude nonlinearity in the repeater. In FM systems, intermodulation noise is mainly caused by transmission gain and delay distortion. Consequently, in FM systems it is a function of the amplitude "Amplitude (physical)") of the signal and the magnitude of the frequency deviation. Thus the characteristics of frequency modulated signals are more suitable for microwave transmission than amplitude modulated signals.

Contenido

Los sistemas de radio por microondas que usan modulación de frecuencia se conocen ampliamente por proporcionar comunicaciones flexibles, confiables y económicas, de punto a punto, cuando usan la atmósfera terrestre como medio de transmisión. Los sistemas de microondas FM que se usan con el equipo multiplexor adecuado son capaces de conducir en forma simultánea desde unos pocos circuitos de voz de banda angosta, hasta miles de circuitos de voz de alta velocidad, audio de calidad comercial y televisión comercial. Los estudios comparativos de costo han demostrado que los sistemas radio por microondas con modulación por frecuencia (FM) es, casi siempre, el método más económico de proporcionar circuitos de comunicaciones cuando no hay ya cables metálicos ni fibras ópticas, o cuando existen duras condiciones de terreno o de clima. También, los sistemas de microondas FM se pueden ampliar con facilidad.

En la figura se ve un diagrama de bloques simplificado de un sistema de microondas de FM. La banda base es la señal compuesta que modula la portadora FM, y que puede abarcar uno o más de los sistemas siguientes.

1. Canal de banda de voz multiplexado por división de frecuencia.

2. Canales de banda de voz multiplexados por división de tiempo.

3. Vídeo compuesto de calidad comercial o teléfono visual.

4. Datos en banda ancha.

5. Ancho de Banda en Fibra Óptica 4,5 MHz.

FM Microwave Radio Transmitter

In the FM microwave transmission shown in the transmitter block diagram, a pre-amplification (pre-emphasis) stage precedes the frequency modulator (FM shifter). This pre-amplification increases the amplitude of the upper baseband signals. Allowing the lower baseband frequencies to modulate the frequency of the IF carrier, and the upper baseband frequency to modulate the phase of that carrier. This block diagram ensures a more uniform signal-to-noise ratio across the entire baseband spectrum. The FM diverter stage delivers the modulation of the IF carrier which at the end becomes the main microwave carrier, normally the typical intermediate frequencies are between 60 and 80 MHz, where 70MHz is most suitable. Low index frequency modulation is used in the FM diverter. Where the modulation indices are kept between 0.5 and 1, in this way a narrowband FM signal is realized at the output of the diverter, consequently the bandwidth of the F1 resembles that of common AM and approaches twice the maximum frequency of the baseband.

The F1 and its associated sidebands are converted to the higher frequencies of the microwave region, using the mixer, microwave oscillator and bandpass filter. To transfer the F1 to the RF stage, mixing and not multiplication is used because the modulation index does not change due to the heterodyning process. Also by multiplying the carrier of F1 the frequency deviation and the modulation index would be multiplied, thus increasing the bandwidth.

Microwave generators consist of a crystal oscillator followed by a series of frequency multipliers. For example a 125 MHz crystal oscillator followed by a series of multipliers, with combined multiplication factor equal to 48, could be used for a microwave carrier frequency of 6 GHz. The channel combining network provides a means of connecting more than one microwave transmitter from a single transmission line feeding the antenna.

FM microwave radio receiver

Receiver Block Diagram: The FM microwave radio receiver is shown, where the channel separator network block provides the isolation and filtering necessary to separate individual microwave channels and direct them to their respective receivers. The bandpass filter, AM mixer and microwave oscillator lower the frequencies from microwave RF to F1, and pass them to the FM demodulator. Where this demodulator is a conventional, non-coherent FM detector. At the output of the FM detector, a de-emphasis network restores the baseband signal to its original amplitude versus frequency characteristics.

Los radios de microondas emiten señales usando como medio la atmósfera terrestre, entre transmisores y receptores, para una mejor emisión y recepción, estos se encuentran en la cima de torres a distancias de 15 a 30 millas. Así los sistemas de radio de microondas tienen la ventaja obvia de contar con capacidad de llevar miles de canales individuales de información entre dos puntos, dejando a un lado la necesidad de instalaciones físicas, tales como los cables coaxiales o fibras ópticas. Así claro esta, se evita la necesidad de adquirir derechos de vías a través de propiedades privadas, además las ondas de radio se adaptan mejor para salvar grandes extensiones de agua, montañas altas o terrenos muy boscosos que constituyes formidables obstáculos para los sistemas de cable.

Entre las ventajas de radio de microondas están las siguientes:.

Radio link

A terrestrial radio link or terrestrial microwave provides connectivity between two sites (earth stations) in line-of-sight (LOS*) using radio equipment with carrier frequencies above 1 GHz. The emitted waveform can be analog (conventionally frequency modulated) or digital.

Microwaves are electromagnetic waves whose frequencies are within the super high frequency spectrum, SHF.

It is also usually offered by WiMAX installers to offer service from places where there is coverage to those nearby where there is not.

Microwave generators are critical generators in terms of operating voltage and current.

One of the means is not to act on the generator or amplifier but to use a pin diode device in the output guide, directly modulating the amplitude of the wave.

Another means is to use a ferrite phase shifter and modulate the wave in phase. In this case it is easy to obtain frequency modulation through the following process:

In a first stage, a low frequency carrier, for example 70 MHz, is FM modulated.

In a second stage, this modulated carrier is mixed with the main carrier at GHz frequency, for example 10 GHz.

A frequency filter passes the sum frequency, 10070 MHz with its 3 MHz side bands and therefore the passband will be from 10067 to 10073 MHz, which is the final microwave signal.

In the receiver, this signal is mixed with the 10 GHz local oscillator followed by a filter that takes advantage of the 70 MHz difference frequency, which is amplified and then detected by the usual FM techniques.

The main frequencies used in microwaves are around 12 GHz, 18 and 23 GHz, which are capable of connecting two locations between 1 and 25 kilometers away from each other. Microwave equipment operating between 2 and 6 GHz can transmit over distances between 30 and 50 kilometers.

Teams.

A radio link is made up of terminal equipment and intermediate repeaters. The function of repeaters is to overcome the lack of visibility imposed by the earth's curvature and thus achieve links higher than the optical horizon. The distance between repeaters is called hop.

The repeaters can be:

The antenna generally used in microwave radio links are of the parabolic type. The typical size is a diameter of about 3 meters. The antenna is rigidly fixed, and transmits a narrow beam that must be perfectly focused towards the receiving antenna.

These microwave antennas must be located at a considerable height above ground level, in order to achieve the greatest possible separations between them and be able to overcome possible obstacles. Without intermediate obstacles, the maximum distance between antennas is approximately 150 km. With repeater antennas, it is clear that this distance can be extended if the curvature of the earth is used, through which microwaves are deflected or refracted in the earth's atmosphere.

For example, two microwave antennas located at a height of 100 m can be separated by a total distance of 82 km, this occurs under certain conditions, such as terrain and topography. That is why this distance can vary according to the conditions handled.

The distance covered by microwave links can be increased by the use of repeaters, which amplify and redirect the signal. It is important to note that signal obstacles can be overcome through passive reflectors.

The transmitted microwave signal is distorted and attenuated as it travels from the transmitter to the receiver; these attenuations and distortions are caused by distance-dependent power loss, reflection and refraction due to obstacles and reflecting surfaces, and atmospheric losses.

Parabolic reflector: It is constructed of fiberglass or aluminum. The fiberglass case is constructed with a laminate reinforced with polyester resin; The surface is metallized with zinc.

Efficiency: in an antenna the gain is reduced for the following reasons:

Climate and terrain are the biggest factors to consider before installing a microwave system.

In summary, in a radio link there are losses due to:

The main use of this type of transmission is in long-distance telecommunications, it is presented as an alternative to coaxial cable or fiber optics.

This system requires fewer repeaters or amplifiers than coaxial cable but requires the antennas to be aligned.

The main uses of terrestrial microwaves are for television and voice transmission.

Microwave links are often used to link different buildings, where cable installation would be problematic or more expensive. However, because terrestrial microwave equipment typically uses licensed frequencies, additional economic and financial limitations are imposed by the licensing organizations or governments.

The main applications of a terrestrial microwave system are the following:

Terrestrial microwaves continue to be a very effective means of communication for metropolitan networks to interconnect banks, markets, department stores and cellular radio bases.

Likewise, radio links can be used to extend Internet coverage, as happens in places where WiMAX did not reach.[2]​.

Before fiber optics, these microwaves formed the heart of the long-distance telephone transmission system for decades.

Microwaves are also relatively cheap. Choosing two simple towers and putting antennas on each can cost less than burying 50 km of fiber through a congested urban area over a mountain, and can also be cheaper than renting fiber from a company that offers telephone service.

The microwave network equipment manufacturers are:[3]​

-Nokia

-NEC

-Ericsson

-Marelli

• Marconi

• GT&E")

• G.E.

• Philips

-Rohde & Schwartz")

-Kuhne")

-Codan")

-Alcatel

• Fujitsu

-Siemens

-ATI

-Hughes

• Ceragon")

-Saf Tehnika")

-Huawei

-ZTE.