Description of microwave technology

Radio systems permanently become commonplace in our reality . Just look around: mobile phones, wireless Internet, or  increasingly, wireless reading such as water meters in our homes. Such systems are needed wherever there is a need for signal transmission without wires . Sometimes out of necessity and sometimes just out of convenience.

The inventor of the radio was Italian Guglielmo Marconi. In 1894, he built the first radio device  and a year later achieved wireless transmission distance 1km.

Electromagnetic waves

But actually how the signal (sound, image, data) from transmitter , through air , reaches the receiver? Everything is based on the laws of physics and electromagnetic radiation. These waves and their corresponding modulation (shaping) are a carrier of information. The radio signal transmission bases on electromagnetic waves would. This wave has a shape of  sinusoid and defined operating frequency and it is a " pattern " to which the wave that reaches the receiver is compared. This wave is modulated (in different ways) by signal, which was sent wirelessly.

The role of antennas in radio transmission

To enable wireless signal transmission, apart from transmitter and receiver also antennas are required. Aerials are necessary to convert electromagnetic waves into an electrical signal and vice versa.

Widmo promieniowania elektromagnetycznego

Microwaves

Radio systems are based on microwaves. Microwaves are electromagnetic waves with a wavelength between infrared and ultra short waves (Fig. 1). Radio frequencies in the microwave range vary from 3kHz to 300GHz. However, not all frequencies in this range can be used to transmit information. Rules for the use of radio frequencies that have a direct connection with the operation of wireless systems are tightly regulated by the relevant authorities. In Poland, the office of legal regulation of use of radio frequencies is the Office of Electronic Communications (UKE). The publication of those regulations belongs to the Ministry of Transport. Based on the Decree of the Minister of Transport dated 3 July 2007, was developed ISM band. The ISM band is license free band , which under certain conditions can by used by anyone to transmit information over radio.

 

The ISM band includes many frequencies adapted to transmit various types of information. CAMSAT as a manufacturer of wireless CCTV security transmission systems, also uses the ISM band  and its products meet all standards associated with radio technology. Therefore the use of CAMSAT wireless products in the European Union is fully permitted and legal.

Frequencies on which CAMSAT products operate are as listed below:

    • 868.000 ÷ 869.000 MHz - Systems for telemetry data transmission, i.e. WCT-02, CD04
    • 5,725 ÷ 5,875 GHz - systems for video/audio signal transmission, i.e. CAM5816h
    • 5,150 ÷ 5.350 GHz - systems for audio/video video signal transmission in digital form, i.e. CDS5021h
    • 5.470 ÷ 5.725 - systems for transmission in Wi-Fi technology ( IP cameras ), i.e. CDS-5IPmini, CDS-5IPmini SMACDS - 5IP 
    • 5.15 ÷ 5,35 | 5,5 ÷ 5,7 GHz – systems for television, designed to transmit audio and video in Full HD, i.e. Black Link HD5Black Link Drone.
Przykład modulacji fali nośnej - modulacja FM

 

RF modulation

 As described earlier, transmission of information over radio is implemented by would wave modulation. There are several types of modulation , but most of them are based on changes of frequency or amplitude. The most famous and used by CAMSAT type of modulation is FM(Frequency Modulation - Frequency Modulation). This is an analog signal transmission system , encrypted in wave would by the instantaneous frequency changes depending on the input signal. FM modulation is used in two most popular CAMSAT product lines : CAM5816 and TCO5807 , used for analogue video/audio signal (PAL / NTSC) transmission.

 

Another way of placing signal in electromagnetic wave is an OFDM modulation. It involves simultaneous transmission of multiple signals on an orthogonal frequencies . In short, this involves more efficient use of the radio spectrum and increasing the rate of data transmission. Instead of one high-speed transmission , it transmits a lot slower streams at different wavelengths, so called subcarriers. This method is used in CAMSAT digital systems, i.e. CDS5021 ( for analog cameras ) and CDS - 5IP ( for IP cameras ). These systems, compared with analogue systems  characterize by a much greater resistance to external interference and the ability to transfer much more information at one time.

The last way is RC2FSK modulation, used in CD04 for telemetry data transmission( signals RS232, RS485 and TTL ). This type of modulation bases on frequency change for digital signals (state high and low).

The range of radio transmission

An important aspect of wireless systems description is the transmission distance, which allows to send the signal without any quality loss . This distance depends among others on :

  • the frequency of radio signal - the lower the frequency the greater permeability through barriers and thus higher possible coverage
  • radiation power of the transmitter (the maximum power is strictly defined by the Office of Electronic Communications )
  • gain of receiving antennas (the use of " bigger" receiving antennas with higher gain  results in operating range increase) 
  • radio signal modulation

 

In case of radio systems very often maximum range LOS (line-of-sight) is declared, described as clear line of sight in first Fresnel zone between the antennas (Fig. 3). Unfortunately, every obstacle reduces operating range or even makes signal transmission impossible.

Pierwsza strefa Fresnela

Summary

What is the future of wireless systems? For sure it is inextricably linked with changes in the ISM band. You can already see that some bands are " overcrowded " (i.e. 2.4 GHz ) and at some point you may just " run out " for new radio equipment. The future will also bring changes in both the quantity and speed of information exchange. Very high-speed Internet  accessible from any place on earth? It slowly  becomes a reality.

 

Wireless systems arose from the need to get rid of cumbersome wires and cables, but nowadays one problem is still not solved  - power cables. We can wirelessly send infinite amount of information, but the wireless energy transfer is still very difficult. I think the future will bring changes also in this case.

 

Michał Życziński, CAMSAT