When an electric charge oscillates, it will produce both electric and magnetic fields that vary sinusoidally with time. The two fields couple with each, such that the two fields are perpendicular to each other, and travel as an electromagnetic wave. This is shown below. All electromagnetic waves are transverse waves that travel at the speed of light (3.0 x 108 ms-1) in a vacuum. The electromagnetic (EM) spectrum is the range of all possible electromagnetic radiation. The electromagnetic spectrum, shown in the chart, extends from just below the frequencies used for modern radio (at the long-wavelength end) to gamma radiation (at the short-wavelength end), covering wavelengths from thousands of kilometres down to fractions of the size of an atom. It is commonly said that EM waves beyond these limits are uncommon, although this is not actually true. The short wavelength limit is likely to be the Planck length, and the long wavelength limit is the size of the universe itself, though in principle the spectrum is infinite. Electromagnetic energy at a particular wavelength λ (in vacuum) has an associated frequency f and photon energy E. Thus, the electromagnetic spectrum may be expressed equally well in terms of any of these three quantities. They are related according to the equation: wave speed (c) = frequency x wavelength where v (or sometimes indicated as c) is 3.0 x 108 ms-1 in a vacuum or air. The table below summarises the different regions of the electromagnetic region. Region Frequency Range (f) / Hz Wavelength Range (l) / m Sources Uses Radio waves <>9 > 10-1 Sparks or alternating current cause a radio antennae to oscillate the atoms within it to the correct frequency Radio, television, mobile phones, magnetic resonance imaging Microwaves 1011 – 109 10-3 – 10-1 Atoms or molecules are oscillated within klystron and magnetron tubes Cooking, long distance communication, radar, terrain mapping Infrared 1014 – 1011 10-7 – 10-3 Oscillation of atoms or molecules due to the absorption of heat energy Heating and drying, night vision cameras, remote controls, satellite remote sensing Visible 7.5 x 1014 4 x 10-7 Oscillation due to heat energy or electron transitions within an atom What the typical eye and film can see Ultraviolet 1016 – 1014 10-8 Electron transitions within an atom Photochemicals, photoelectric effects, hardening casts in medicine X-rays 1019 – 1016 10-11 Electron transitions or braking Medicine, crystallography, astrophysics, remote sensing Gamma Rays > 1019 <>-11 Nuclear transitions Nuclear research, geophysics, mineral exploration. Another problem with long distance communications is the attenuation of the transmitted signal - it decreases in strength as distance from the transmitter increases. You notice this as the radio station you are listening to on a long drive begins to lose reception as your distance from home increases. This problem can be remedied by transmitting at a very high power, or by amplifying the signal at the reception point. Amplification is essential if the transmission uses repeater stations or when the signal goes via a satellite. The mathematical relationship between the intensity of the energy falling on a given area and the distance of that area from the source of the energy is known as the inverse square law, summarised by the expression (right). Where I = intensity of energy per unit area, and d = distance from source (m). Communicating With Electromagnetic Waves Modulation Waves carry energy from one place to another. If the amount of energy they carry varies constantly, they can also carry information. The energy variations act as a type of "code". Light, radio and microwaves can be encoded in this way. Information can be added to a carrier wave by either superimposing signals of varying frequency (or wavelength, since these are dependent on each other), or signals of varying amplitude. Adding information in this way is known as modulation. If the information is added by superimposing a wave with varying frequency, we have frequency modulation or FM. If it is added by superimposing a wave with varying amplitude we have amplitude modulation or AM. Amplitude modulation (AM) Frequency modulation (FM) Modulation of radio waves The information transmitted by the many radio and TV stations is very similar. They all need to broadcast information with the same frequencies (20 Hz to 20 000 Hz - the range of human hearing) and amplitudes. If they did so, then we would not hear any of them clearly. All the different signals from the different stations would interfere with each other and we would receive a jumbled mess. To avoid this problem, each station is assigned a particular broadcast frequency (the carrier wave) onto which they superimpose the data they wish to transmit using the frequencies in a narrow band either side of the carrier frequency. This range of frequencies is known as the band width of that radio station, while the carrier wave frequency is the tuning frequency - the one we turn our dial to receive that station. Circuitry in the receivers decode the information and process it into the appropriate sound wave frequencies. Receivers can be tuned to pick up the carrier wave, and because no two radio stations have the same carrier wave, they should not interfere with each other. In fact, they still do a little some times because there are so many stations using a limited range of the electromagnetic spectrum, that the carrier waves of different stations are not very different to the carrier waves of other stations. Circuitry in the receiver subtracts the carrier wave from the combined signal, interprets the frequency or amplitude variations in the signal wave and produces the sounds we hear from our radios or TV. This process is known as demodulation. Advantages and Disadvantages of AM and FM radio transmission AM uses a much narrower range of frequencies than FM, so many more AM stations fit into the limited radio bandwidth of the electromagnetic spectrum. However, it is much easier for circuitry in receivers to filter out variations in amplitude in an incoming FM signal than it is to filter out frequency variations in an incoming AM signal, so FM reception is usually much clearer than AM reception. For this reason, it is the preferred way to broadcast music - hence TV music concerts with "simulcast FM radio sound". Microwave modulation Microwaves are also modulated to carry information. Because the available band width for microwas is greater, and because there are not as many users, microwaves are used to transmit mobile phone and Internet cable data. This also means that many more signals can be added to the same carrier wave. Up to 20 000 independent signals can be transmitted simultaneously on a single carrier wave. In addition, because their wavelength is smaller, the carrier waves do not spread out as much as radio waves, so more data and more reliable data reach receivers. Visible light modulation Visible light is also used to transmit data. High energy laser light with a fixed but small frequency range is amplitude modulated to carry data. Because the frequency range within a laser beam is very narrow, FM is not efficient so amplitude modulation is used. In addition, the narrow frequency range of a laser means it suffers more from interference than the alternate, broader band communications by radio or microwave. Their use in open air communications is therefore very limited - reliable only to about 200 m distance. Laser transfer of data requires fibre optic cable if the data is to be transmitted more than 200 m to eliminate external interference.
– 4.3 x 1014
– 7 x 10-7
– 7 x 10-7
– 10-8
Saturday, June 20, 2009
Electromagnetic Waves
Transmitting by Radio
One of the problems with long wires is that the resistance of the wire can cause quite a large voltage drop, so the aircraft's computer will not receive the data properly, and therefore will not respond to them. 10 000 metres up this could be catastrophic. An in a big brute like the Antonov 225, this could be a big problem. The way out is to combine the data with a carrier wave. This is done in the same way as broadcasts are combined with a carrier wave before transmission from a transmitter. In Amplitude Modulation (AM) transmission, the signal wave and the carrier wave are superposed as shown: The amplitude varies. At the other end the signal wave is removed by a process of demodulation. The process is relatively easy (hence cheap) but can be prone to noise. AM radio is particularly prone to interference by electric motors, or by waves travelling by different paths to the receiver. Frequency modulation uses variations in the frequency of the carrier wave, as shown in the picture below: If the signal voltage is raised, the frequency is raised and vice versa. The carrier wave is still removed by the receiver (demodulation) to recover the information signal. The advantage of FM over AM is that the signal is less prone to noise. Both of these methods use analogue signals (signals that vary continuously). With analogue signals, there can be problems if the signal has been changed. There might be distortion making a broadcast unpleasant to listen to. In an aeroplane, it could result in a computer interpreting data incorrectly. Data are more reliably transmitted if they are converted into digital form (pulses that are ON or OFF). The process of pulse code modulation involves an analogue signal being translated into a series of binary numbers. This in turn is represented by a series of ON and OFF pulses (1 and 0). The advantages of this are: As long as the voltage in the wire is above a "cut-off" value, the signal is interpreted as a 1. The computer can read the data directly with out having to turn them into digital form. Checks can be built into the number stream. The picture shows the idea. The voltage is sampled at regular intervals to give an output shown by the blue lines. There are a couple of problems: The sampling may not faithfully reflect the shape of the wave. Increasing the sampling rate reduces this problem. Spurious frequencies may arise. This is called aliasing. This again is reduced by increasing the sampling rate. Sampling should be done at at least twice the frequency of the highest frequency. In coding we need to assign a value to each sample. However, binary numbers are whole numbers; we cannot do fractions in binary. Each voltage is assigned a binary whole number value. This is called quantisation. The values are discrete, not continuous. If you look carefully at the arrows on the picture above, you will see that some of the lines have not reached the value of the analogue signal. They are slightly above or slightly below. This problem can be reduced by increasing the number of levels available. In 4-bit (bit = binary digit) code, there are 8 levels. 8-bit codes give 256 levels. Many computers use 32-bit or even 64-bit codes. The picture shows how samples are quantised into 8 levels: In binary we can't have negative numbers. So we put the zero line half way up the quantum levels, at level 0100 (4). We can now turn these samples into a series of binary numbers. And then turn them into pulses: Low amplitude signals are particularly prone to distortion as the "rounding factor" is a greater proportion of their value. We get around this by to have more steps in the lower voltage ranges. The signals are compressed. When they are decoded the signal are expanded. The whole process is described by the ghastly word companding. We see, hear and sense with analogue signals. The position of the control surfaces in an aeroplane is a continuous variable. It would be highly undesirable to have them in discrete steps, otherwise the plane will be climbing or descending, with a very brassed-off pilot. So we need a way of converting analogue signals to digital and back again. Analogue signals are converted to digital signals with an analogue to digital converter (A-D converter). A simple way of doing this is by generating a series of voltage steps (a ramp voltage) and comparing the analogue voltage with this with a circuit called a comparator. An operational amplifier (op-amp) is used to convert digital signals back to analogue. The op-amp is not a very spectacular component, but is very useful. It can be used in a number of configurations. The op-amp has two inputs: Inverting input (marked "-"); Non-inverting input (marked "+"). It has a single output. It amplifies the difference between the two inputs. The ideal op-amp has: Infinite input impedance; Infinite gain (amount by which it amplifies). It is most commonly used in a configuration called an inverting amplifier. The basic circuit is shown below: In this case the input is fed into the inverting input. A couple of key points: Since the non-inverting input is connected to the zero volt line, and the voltage difference between the two input is very small indeed, we say that the inverting input is at zero volts. We call it a virtual earth. Since the input resistance of the non-inverting input is extremely high, the current going in is negligible. So we can say that all the current flows from Rin to Rf. The current will be the same through Rin and Rf. Therefore: The minus sign tells us that the voltage is climbing up from the zero point. We can therefore say: Therefore the voltage ratio is equal to the ratio of the resistances. If we add a second parallel resistor to the inverting input, we can get the sum of the two voltages: Since: Itot = I1 + I2 we can use Ohm's Law to write: -Vout = V1 + V2 Rf R1 R2 If the values of the input resistors are the same, we get the sum of the two voltages (with a negative sign). This is called a summing amplifier. For digital to analogue conversion, we need to use a number of parallel input resistors which are in the ratio 1: 2: 4: 8: 16 etc. In aeroplanes the saving of weight is critical. If we can have one wire feeding several sensors, that saves a lot of weight. We use a technique called multiplexing to splice the output of each sensor before it is sent down the wire to the computer. In time division multiplexing (TDM) the data from each sensor are split up into equal sections of time. They are then sent down the wire to a demultiplexer, where they are reassembled , giving as many outputs as there were inputs. TDM is often used in trains where a single wire carries the control signals from the remote driving cab to the locomotive. Frequency division multiplexing (FDM) adds the data to a carrier wave of a certain frequency. A number of carrier waves are sent down the wire. At the other end the correct signals are filtered out using electronic filters. The data are demodulated, before being fed to the control circuitry. More recent developments include digital position sensors. A Perspex strip is set between a range of several light emitting diodes(LED) and corresponding photodiode. There are clear and opaque regions on the strip. Light gets through the clear strip to turn on the photodiode, giving a 1. The dark regions prevent the light getting through, so the photodiodes give out a 0.Pulse Code Modulation (PCM)
Quantisation
Conversion
Analogue to Digital
Digital to Analogue
Multiplexing
Digital Sensors
Frequency modulation
Variation of the frequency of a carrier wave (commonly a radio wave) in accordance with variations in the audio signal being sent. Developed by American electrical engineer Edwin H. Armstrong in the early 1930s, FM is less susceptible to outside interference and noise (e.g., thunderstorms, nearby machinery) than is AM. Such noise generally affects the amplitude of a radio wave but not its frequency, so an FM signal remains virtually unchanged. FM is also better able to transmit sounds in stereo than AM. Commercial FM broadcasting stations transmit their signals in the frequency range of 88 megahertz (MHz) to 108 MHz. For more information on FM, visit Britannica.com. Britannica Concise Encyclopedia. Copyright © 1994-2008 Encyclopædia Britannica, Inc. (1) An earlier magnetic disk encoding method that places clock bits onto the medium along with the data bits. It was superseded by MFM and RLL.FM
in full frequency modulationfrequency modulation
(2) Varying the frequency of the waves of a carrier in order to transmit analog or digital data. Frequency modulation (FM) is widely used in audio transmission, not only for its namesake FM radio, but for the audio channels in television. See modulation and carrier.Vary the Angle In FM modulation, the frequency of the carrier wave is varied by the incoming signal. In this example, the modulating wave implies an analog signal. Digital Frequency Shift Keying (FSK) For digital signals, frequency shift keying (FSK) uses two frequencies for 0 and 1 as in this example.
Cameras and lenses made simple
The imaging device: CCD means a Charged Coupled Device and consists of a flat array of tiny, light sensitive photodiodes. Each diode produces a voltage that is directly proportional to the amount of light falling on it. No light would produce no voltage and therefore a black level. Maximum light would produce a maximum voltage and therefore a white level. In between these would be shades of grey, and is the luminance information of a video signal. In the case of a colour camera, a chrominance signal is superimposed onto the luminance signal to carry the colour information. (If a colour camera is connected to a monochrome monitor, then a monochrome picture would be produced from the luminance information and the chrominance would not be processed). See also colour cameras with separate Y/C outputs under resolution. The range of light levels that a CCD can cope with is very limited, therefore means have to be introduced to restrict the light range within certain limits. The video signal: A field of video is created by the CCD being scanned across and down exactly 312 1 / 2 times and this reproduced on the monitor. A second scan of 312 1 / 2 lines is exactly 1 / 2 a line down and interlaced with the first scan to form a picture with 625 lines. This is known as a 2:1 interlaced picture. The combined 625 line is known as a frame of video and made up from two interlaced fields. The total voltage produced is one volt from the bottom of the sync pulse to the top of the white level, hence one volt peak to peak(p/p). The luminance element of the signal is from 0.3 volts to one volt, therefore is 0.7 volts maximum. This is known as a composite video signal because the synchronising and video information are combined into a single signal. Note that the imaging device is scanned 625 times but the actual resolution is defined by the number of pixels making up the device. There are several factors that make up a complete camera specification and are all be inter-related. These are: Sensitivity Signal to noise ratio. Automatic gain control. Resolution. Sensitivity: The most common factor people look for in a camera specification is the sensitivity, although it is not always the most important. Sensitivity is the amount of light, in lux, necessary to produce a video signal of some, usually unspecified, level. This factor seems to be the marketing battleground upon which all manufacturers fight to show their cameras as being better than the competition! Signal to noise ratio. (S/n). As seems obvious this is the ratio of the level of the video signal to the amount of noise present. Noise in a video is seen as snow or graininess, resulting in a poorly defined image on the monitor or video recording. The unit for expressing s/n ratio is decibels (dB), but do not be too worried because it can be expressed as a ratio. The following table shows the equivalent ratio for values given in dB. dB Ratio 100 100,000:1 60 1,000:1 50 316:1 40 100:1 30 32:1 20 10:1 10 3:1 S/N ratio dB S/N ratio:1 Picture quality 60 dB 1,000 Excellent, no noise apparent 50 dB 316 Good, a small amount of noise but picture quality good. 40dB 100 Reasonable, fine grain or snow in the picture, fine detail lost. 30 dB 32 Poor picture with a great deal of noise. 20 dB 10 Unusable picture. Automatic gain control (AGC). When the light falling on to an imaging device reduces to a certain level, there is insufficient to create a full level video signal. AGC acts to increase the amount of amplification in these conditions to bring the signal up to the required level. As well as amplifying the video signal, additional noise can be introduced, and the signal to noise ratio reduced. The result is frequently a very much degraded signal and poor picture on the monitor. Resolution. The value referred to here is the horizontal resolution in TV lines, that is the number of black to white transitions that can be resolved across the image. This is a function of the number of pixels that make up the CCD imaging area and the bandwidth of the camera circuitry. Typical camera resolution is 350 TV lines, with high resolution cameras producing better than 450 lines. Note that resolution costs money! There are now colour cameras that instead of superimposing the chrominance onto the luminance signal, provide the chrominance as a separate signal. This is known as Y/C separation and requires two coaxial cables from the camera to carry each signal separately. The effect of this technique is to increase the bandwidth and therefore the resolution, typically to better than 500 TV lines.912 words. introduction The human eye is an incredibly adaptable device that can focus on distant objects and immediately re-focus on something close by. It can look into the distance or at a wide angle nearby. It can see in bright light or at dusk adjusting automatically as it does so. It also has a long 'depth of field' therefore scenes over a long distance can be in focus at the same time. It sees colour when there is sufficient light but switches to monochrome vision when there is not. It is also connected to a brain that has a faster updating and retentive memory than any computer. Therefore the eyes can swivel from side to side and up and down, retaining a clear picture of what was scanned. The brain accepts all the data and makes an immediate decision to move to a particular image of interest. It can then select the appropriate angle of view and re-focus. The eye has another clever trick in that it can view a scene of great contrast and adjust only to the part of it that is of interest. By contrast the basic lens of a CCTV camera is an exceptionally crude device. It can only be focused on a single plane, everything before and after this becomes progressively out of focus. The angle of view is fixed at any one time it can only view a specific area that must be predetermined. The iris opening is fixed for a particular scene and is only responsive to global changes in light levels. Even an automatic iris lens can only be set for the overall light level although there are compensations for different contrasts within a scene. Another problem is that a lens may be set to see into specific areas of interest when there is a lot of contrast between these and the surrounding areas. However as the sun and seasons change so do light areas become dark and dark areas become light so the important scene can be 'whited out' or too dark to be of any use. One of the most controversial but important aspects of designing a successful CCTV system is the correct selection of lens. The problem is that the customer may have a totally different perspective of what a lens can see compared to the reality. This is because most people perceive what they want to view as they see through their own eyes. Topics such as identification of miscreants or number plates must be subjects debated frequently between installing companies and customers. The selection of the most appropriate lens for each camera must frequently be a compromise between the absolute requirements of the user and the practical use of the system. It is just not possible to see the whole of a large loading bay and read all the vehicle number plates. The solution may be more cameras or viewing just a restricted area of particular interest. The company putting forward the system proposal should have no hesitation of pointing out the restrictions that may be incurred according to the combination of lens versus the number of cameras. Better this than an unhappy customer who is reluctant to pay the invoice. Fixed Focal Length These are sometimes referred to as monofocal lens. As the name implies this type of lens is specified when the precise field of view is fixed and will not need to be varied when using the system. The angle of view can be obtained from the supplier's specification or charts provided. They are generally available in focal lengths from 3.7mm to 75mm. Longer focal lengths may be produced by adding a 2x adapter between the lens and the camera. It should be noted that this will increase the f number by a factor of two (reducing the amount of light reaching the camera). If focal lengths longer than these are required then it will be necessary to use a zoom lens and set it accordingly. Except for very wide angle lenses all other lenses have a ring for adjusting the focus. In addition cameras include a focusing adjustment that moves the imaging device mechanically relative to the lens position. This is to allow for minor variations in the back focal length of lens and manufacturing tolerances in assembling the device in the camera. Correct focusing requires setting of both these adjustments. The procedure is to decide the plane of the scene on which the best focus is required and then set the lens focusing ring to the mid position. Then set the camera mechanical adjustment for maximum clarity. Final fine focusing can be carried out using the lens ring. The mechanical focusing on cameras is often referred to as the back focus. This was because a screw at the back of the camera moved the tube on a rack mechanism. Modern cameras now have many forms of mechanical adjustment. Some have screws on the side or the top, some still at the back. There are cameras that have a combined C/CS-mount on the front that also has the mechanical adjustment and can accept either type of lens format. The longer the focal length of the lens the more critical is the focusing. This is a function of depth of field. Variable Focal Length This is a design of lens that has a limited range of manual focal length adjustment. It is strictly not a zoom lens because it has quite a short focal length. They are usually used in internal situations where a more precise adjustment of the scene in view is required which may fall between two standard lenses. They are also useful where for a small extra cost one lens may be specified for all the cameras in a system. This saves a lot of installation time and the cost of return visits to change lenses if the views are not quite right. For companies involved in many small to medium sized internal installations such as retail shops and offices this can save on stockholding. It makes the standardisation of systems and costing much easier. Manual Zoom Lens A zoom lens is one in which the focal length can be varied manually over a range by means of a knurled ring on the lens body. It has the connotation of 'zooming in' and therefore infers a lens with a longer than normal focal length. The zoom ratio is stated as being for instance 6:1 this means that the longest focal length is six times that of the shortest. The usual way of describing a zoom lens is by the format size, zoom ratio and the shortest and longest focal lengths, i.e. 2/3," 6:1, 12.5mm to 75mm. Again, great care must be taken in establishing both the camera and the lens format. The lens just described would have those focal lengths on a 2/3" camera but a range of 8mm to 48mm on a 1/2" camera. Similarly a lens giving the same performance on a 1/2" camera would be a 1/2," 6:1, 8mm to 48mm. Motorised Zoom Lens Manual zoom lenses are not widely used in CCTV systems because the angle of tilt of the camera often needs to be changed as the lens is zoomed in and out. The most common need for a zoom lens is when used with a pan tilt unit. The lens zoom ring is driven by tiny DC motors and controlled from a remote source. With a correctly set up camera lens combination the focus should not change from one limit of zoom to the other. With the development of ever smaller cameras and longer focal length lenses the method of mounting the camera/lens combination must be taken into account. There are many cases where the lens is considerably larger than the camera and it may be necessary to mount the lens rigidly with the camera supported by it. In other cases it may be necessary to provide rigid supports for both camera and the lens. Always check the relationship between the camera and lens sizes and weights when selecting a housing or mounting. Most manufacturers of housings can provide lens supports as an accessory. The most frequent reason for the focus changing when zooming is that the mechanical focus of the camera has not been set correctly. Motorised Zoom Lens With Pre-sets There are many situations where it is required to pan tilt and zoom to a predetermined position within the area being covered. It is possible to obtain motorised lenses with potentiometers fitted to the zoom and focusing mechanisms. These cause the lens to zoom automatically and focus to the setting by measuring the voltage across the potentiometer and comparing it with the signals in the control system. All other functions are as for motorised zoom lenses. Pre-set controls are only possible with telemetry controlled systems. The specification of the telemetry controls should be checked to see whether the pre-set positions are set from the central controller or locally from the telemetry receiver. 1. CAMERAS
The subject of specifying cameras is a jungle of jargon and misinformation, this brief article attempts to shed a little light on some of the mysteries surrounding it. Only CCD cameras will be considered because they are now the most commonly used type for CCTV.2. LENSES
Friday, June 19, 2009
Defeat and Revivial of Tubes
In the 1950s new technology put cables ahead of radio. Small vacuum tubes that could operate under water for 20 years or more meant that amplifiers could be buried at sea with the cable. This boosted the cable's information capacity to the point that it could even carry telephone signals.
Small vacuum tubes like this could be buried at sea with the cable for years. They helped to increase a cable's information-carrying capacity by more than a thousandfold.Vacuum tube, 1958
National Museum of American History, from TyComIn 1956 AT&T teamed up with the British General Post Office to lay two cables across the Atlantic, each transmitting in a single direction. Together they could carry 36 telephone channels, and this soon expanded to 48. Other telephone cables soon followed, and the old telegraph cables became obsolete.
The new cables had a central copper conductor surrounded by a second coaxial conductor that provided a "return" path for the electricity. Instead of gutta percha, the insulator was polyethylene, a synthetic plastic that had been developed in the 1930s.TAT-1, the first transatlantic telephone cable, 1956
National Museum of American History, from Robert Lynch, Director, System Implementation, TyComLaying telephone cable by ship, 1960s
Photograph by Ian RowanTransatlantic telephone cables
Courtesy of Corning, Inc.TAT-1 1956 - 48 channels
Nefoundland - ScotlandTAT-2 1959 - 48 channels
Newfoundland - FranceCANTAT 1961 - 80 channels
Newfoundland - ScotlandSCOTICE-ICECAN 1961-62 - 24 channels
Newfoundland - ScotlandTAT-3 1963 - 138 channels
New Jersey - EnglandTAT-4 1965 - 138 channels
New Jersey - FranceTAT-5 1970 - 845 channels
Rhode Island - SpainCANTAT-2 1974 - 1,840 channels
Nova Scotia - EnglandTAT-6 1976 - 4,000 channels
Rhode Island - FranceTAT-7 1978 - 4,000 channels
New Jersey - England
History of Television in Brazil
I am a vintage TV set collector from Brazil, and I am sending to you some information about the early days of TV in Brazil, which was the first country to have TV in the Southern Hemisphere, and, I believe was also the first country in the Southern Hemisphere to manufacture TV sets. Attached are pictures of the early days of Brazilian television as well as pictures of the early TV sets made here and the factory that made them.
In the second half of the 1940's, many wealthy, (and others not so wealthy, but technically skilled), people made some kind of effort to bring television to Brazil. The honor finally went to one of the most controversial figures in Brazilian history, Mr. Assis Chateaubriand, a very powerful media tycoon in Brazil from the mid 20's to the late 60's. In the late 40's his empire had 34 newspapers in different cities, 36 radio stations and the most important Brazilian national magazine. He decided that he wanted to own a TV station in 1944, when he visited the US for the first time. He visited the RCA facilities in New York, a special guest of David Sarnoff himself, since he was spending large amounts of money on buying radio broadcast equipment for his stations. He was absolutely thrilled by the television experiments he saw at RCA, and immediately decided that, as soon as the war was over, he wanted to buy a TV station. The reaction of David Sarnoff was very curious. He was not at all enthusiastic to Mr. Chateaubriand plans. Sarnoff said that it was very early to think of bringing TV to Brazil, and that Mr. Chateaubriand would do better by strengthening his radio network. It seems that Mr. Sarnoff was very eager to sell radio broadcasting gear and helping on the formation of a large radio network to cover the whole of South America. But he didn't knew Mr. Chateaubriand, who was a very headstrong man, that would never stop until things were done his way. So, Sarnoff was finally convinced to sell not only one, but two TV stations, one for the city of São Paulo ( the economic heart of Brazil ), and other for the city of Rio de Janeiro, which was the capital of Brazil at that time.
In 1947, after spending three years raising money from various sources (for the 5 million dollar investment of buying two television stations was huge even for him), Mr. Chateaubriand placed the order for the equipment. Them, something interesting happened. The people of RCA asked Mr. Chateaubriand to pay, but to wait some time more for the delivery of the equipment, to wait until they thought it was the best time to build it. It cost a three year delay, but it also meant a significant improvement in the broadcasting power of the station. By Mr. Chateaubriand's own words "in 1947 the range of television signal was of twenty miles. Today [1950] a 5 kilowatt transmitter like the one we have here reaches 80 miles". So, TV in Brazil should have started in 1947, but thanks to the foresight of the RCA Victor engineers it began three years later with greater broadcast power.
The RCA Victor equipment was bought for the São Paulo TV station, while for Rio de Janeiro the equipment was built by General Electric. For reasons unknown to me, the Rio station operated on the European standard (625 lines, 25 frames, 7-mc channel, FM sound), while the other station operated on the American 525 lines, 30 frames, 6-mc channel, FM sound, standard. At that time other entrepreneurs were seeking licenses for TV operation, but Mr. Chateaubriand's powerful influence on the Brazilian government blocked them getting the license before his TV went on the air - he wanted the honor to be the pioneer not only in Brazil, but on the whole of Latin America.
Unfortunately for him, Mexican TV actually began operating 18 days before his station. He was now the second in Latin America, but still the first in the Southern Hemisphere. On September 18, 1950, his São Paulo TV station, PRF3 TV Tupi channel 3 was officially inaugurated, with the blessings of the city's catholic bishop and the transmission of a variety show at 9:00 pm. It was a one hour show, and when it was over the station signed off, to resume transmissions only on the following night. All TV sets in use in the city were imported from the USA and a few from Phillips in Holland. TV sets were strategically placed on some key locations, so the largest number of people could witness the miracle of television. To this day, it is still reported that only 200 families in the city had TV sets on that opening night, but this claim is very difficult to prove. Interesting to note is that a major event like that was widely boycotted by the press, with the newspapers not mentioning it. Only Mr. Chateaubriand newspapers and his magazine promoted the advent of television in Brazil.
At that point the station of Rio de Janeiro was still doing test broadcasts.
It is reported that, by the end of 1950 there were 1000 to 2000 TV sets in Brazil, all of them in these two cities. On January 20, 1951, the Rio station, PRG3 TV Tupi channel 6 was officially inaugurated.
In 1955, six stations were on the air in Brazil: three in São Paulo, two in Rio, and one in the state of Minas Gerais, but only in 1956 a precarious TV link was established between the states of Rio and São Paulo. This was hailed by the press as a great achievement, for now peoples in the two cities could see the same programs, but the fact is that until the late 1960's this link was only used on special occasions. In 1956 200,000 TV sets were in use in the country. Brazil had almost 70 million inhabitants. Estimated TV audience was one million people. 90% of the programs were live staged, very little was filmed, and that's why almost no recording of the first decade of Brazilian TV exists. One of the highlights of TV at the end of that decade (when TV stations were now operating on 10 of the 23 states of the nation ) was the transmission to Rio, São Paulo and Minas Gerais of the inaugural ceremonies of the new capital city of Brazil, Brasilia, on April 21, 1960.
The new capital was located on the heart of the country, and this three states on the southeast. A very complicated arrangement was made for the live transmission: three DC3 planes equipped with TV relay gear flew in circles, at different locations, one beaming the signal to the other, and the last one beaming to the ground, and then the ground station beaming to the local TV stations. It didn't work very well, what people saw were very fuzzy images, if any. Better coverage of the inauguration was shown hours later, when the video tapes arrived.
Real network TV in Brazil was only made possible in 1969, after the government made a huge investment in satellite receiving equipment and in microwave systems. The peculiar geography of the country acted as an obstacle to network TV in the 50's and 60's.
Screen shots taken in the 1950's of live advertising on Brazilian TV
A lucky family watching the inaugural broadcast on September 18, 1950 on a GE set.
A crowd gathering in a grocery store to watch the inaugural broadcast of Brazilian television | Building of the State Bank of São Paulo in 1950, with the transmitting antenna of channel 3 on the top.
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Former Hollywood star and international singer, Mexican priest Jose de Guadalupe Mojica visiting the control room of PRF3 TV on June/July of 1950.
| Logo or test pattern of channel 3 of São Paulo |
Studios of PRF3 TV of São Paulo in 1951
| Studio crew of PRF3 TV rehearsing before the start of the night's program's in 1950.
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TV manufacturing in Brazil began in 1952. The first factory was Invictus, which really started the electronic industry in Brazil in 1943. Prior to 1943, all radio sets in use in Brazil were imported. A few attempts of creating an electronic industry were made in the 1930's but they all failed due to strategic errors and lack of maturity of the market and the economy in general. In 1943 the industry and the nation's economy were stronger, and that, combined with the difficult of importing radio sets due to the war, and the Brazilian government's need of a local industry to supply communication gear to the armed forces, led to the rise and boom of a local electronics industry. Located in the industrial state of São Paulo, Invictus was the first, and during the 40's other industries appeared, and also some American and European manufactures began producing in Brazil. The Invictus factory was located in a small building, but in 1945 they were already producing 15.000 radios a month. As soon as television was introduced in Brazil, they began to develop prototypes of TV sets. In early 1952 they released their first TV set on the market, a 17 inch screen model, which had 50% of parts and components made in Brazil. By 1953 the level of "nationalization" of their TV sets was 75% .
After they begun production many other brands began the production of TV sets in Brazil. It is estimated that 80 different manufacturers of television sets were operating in Brazil in the 50's and 60's.
Unfortunately, most of this factories were small businesses, with limited resources and small production. Almost all of them (including the pioneer Invictus) were crushed after 1972, when color TV began in Brazil. They simply were not ready for color TV. The government favored the Japanese and European transnationals, who had the know how to build color sets and the vast resources to build huge factories for mass production of TVs. So, to this day, almost all of the electronic industry here is in the hands of foreigners.
One final note: the first Brazilian TV stations that went on the air in 1950 and 1951 are no longer on the air. They (and all other TV stations from Mr. Chateaubriand's empire, 18 stations in total), faced a tremendous financial crisis in the 70's due to decades of mismanagement, and were declared bankrupt in 1980. Some of the radio stations, many of the newspapers and the national magazine were also declared bankrupt on that same occasion. The assets of the TV stations were sold to other groups, and they are now part of other networks. Mr. Chateaubriand didn't lived to see the downfall of his media empire: he died in 1968, at the age of 75.
Benno Hirschfeld and Bernardo Kocubej, founders of the Invictus factory.
Workers of the Invictus factory in front of the factory in 1953
| Workers of Invictus packing a TV set in 1952 or 53 |
Late 1952 magazine ad promoting the above set, a radio/TV combination, with a 21 inch screen.
| The first model of TV released by Invictus (early 1952), a 17 inch screen set. |
PHILCO TEST EQUIPMENT
PHILCO TEST EQUIPMENT Model 012 Output Meter using a shadow meter as an indicator. 1935Model 055 Speaker Tester, 1936 Model 025 Circuit Tester Model 099 Set Analyzer, 1936 Model 050 Tube Tester, 1941 Automatic Station Setter. This unit was also made without the wooden carrying case. Model 027 Vacuum Tube Voltmeter (VTVM), mid 1930s.
From the Wendall Hall Collection; photo by Joe BookerModel 044 Audio Generator, mid 1930s.
From the Wendall Hall Collection; photo by Joe BookerTube Tester, mid 1930s.
From the Wendall Hall Collection; photo by Joe BookerModel 077 Signal Generator, mid 1930s.
From the Wendall Hall Collection; photo by Joe BookerVibrator Tester, mid 1930s.
From the Wendall Hall Collection; photo by Joe Booker
