Chas' Life, TECHNOLOGY, 1940's to 2010
I have a life long interest in anything technical.
Back in 1943 I was listening to those 10 or 12 inch records on my mum's wind up grammar phone. An on / off lever was used to release a brake which stopped the platter turning. At the age of about 2 or 3 I was allowed to put the record on and carefully place the pick up to hear the sound. The needle in the wiggly groove on the record vibrated a diaphragm and the sound was amplified by travelling down a tube into the box and came out the front. The box was made of wood and produced a pleasant tone. The machine needed winding up and just about managed to play one side of a 12 inch record at 78 Revolution Per Minute. Many records were 'strict dance tempo', waltz, quickstep, foxtrot etc. One favourite was 'Tubby the Tuba' by Danny Kay. A story about an orchestra playing different instruments. It was on both sides of a 12 inch record and I had to wind up to play the other side. One funny record was the laughing policeman. Granddad had an electric record player. It still had a large needle which picked up the sound. This vibrated a magnet inside a coil, I think. This produced an electrical 'signal' which was then amplified and fed to a large speaker. Its volume and tone could be adjusted. Older records got scratched and produced crackles and pops.
These were electric, of course. A 'wind up' radio did not exist then. I wonder if a steam radio will ever be invented. The radio had a large dial and turning the control tuned into many different stations. It was fascinating to hear the whistles and pops being produced while tuning in to a voice or music. The sound was produced from one speaker then. Mono sound. The BBC transmitted The Light Program on 'Long Wave'. The Home Service and The Third Program both on 'Medium wave'. The crackles, whistles and pops got worse in the evening as the sun went down. Not just voice and music. Messages in the form of dots and dashes have been transmitted using Morse Code ever since Marconi invented radio. In fact Morse Code was used by Telegraph before radio was used. Telegraph used wires to transmit the messages but radio was wireless! Our grand parents talked about listening to the 'wireless'.
Both Records and Radio used the natural amplitude sound waves. These were affected by scratches or the natural radiation from the sun and outer space. Loud sounds produced large signals and quiet sounds produced small signals. High 'treble' notes produced high frequency sound signals while low 'Bass' notes produced low frequency sound signals.
Amplitude Modulation (AM)
Audio frequency signals cannot be transmitted directly. Radio signals are much higher frequency. It is these radio signals that you tune to in order to listen to different programmes. Each radio frequency is amplitude modulated by the analogue signal from the broadcasting companies programme. AM radio is noisy because it suffers from natural radiation.
Frequency Modulation (FM)
The AM signal is a single fixed radio frequency. Modulating the radio frequency by changing it's frequency prevents interference from natural radiation. An FM radio can convert the FM signal into an analogue signal which is the one you listen to. No more crackles and pops.
Stereo and Hi Fi Sound
You have two ears. They pick up sound and you can tell where it comes from. So two sound signals are required, one for each ear. The wiggly groove on a record has two sides. So one groove can have two signals. Then record players had two speakers. Placing the speakers at least 8 feet apart in front of you produced a remarkable effect. With ear phones the sound was inside your head!
High Fidelity sound, Hi Fi, was all the rage in the 60's and 70's with long playing records made of vinyl. A clean new record would produce an excellent sound but over time dust and scratches would produce those crackles and pops. Because the system of replaying the sound relied upon a fine needle running in that wiggly groove. The records turning at 45 or 33 Revolutions Per Minute.
Now Hi Fi sound technically is 50 cycles a second up to 20 thousand cycles a second. This is actually what your ears are sensitive to. 50 is a low tone and if you are young you can just hear the squeak of 20 thousand. Cats and dogs can hear these high frequencies better than you. These frequency values are 50hz to 20khz. FM radio has a better frequency response than AM. Radio. Experiments were being made with stereo sound. By now many households had a radio and television. I remember on a Saturday setting them up to listen with the TV on one side and the radio on the other. Then radio transmitted stereo on FM.
When these became available to the general public we were able to record our own voice! It did not sound the same, hearing your own voice, as every body else could hear it! Now this device used magnetic tape. We know that moving a magnet near a coil of wire produces electricity. It also works the other way. Electric current in the coil makes a magnet! The head has a coil of wire inside so, passing the tape past it when an electric signal was applied to the coil, a magnetic signal was recorded on the tape. Then when you passed the tape across the head an electric signal was produced! The signal was analogue, the louder the sound the bigger the signal. It proved difficult to produce a Hi Fi sound due to electro magnetic and moving tape problems. Despite this, tape was used a lot to record music off the radio at home and playing pre recorded tracks. Compared to true sound it was like listening through cotton wool! Only recording studios could afford the professional tape machines.
These recorders could record several tracks on wide tape at high speed. To record music required a lot of tape. Much of my later working life was with a company producing Industrial Recorders. These were mainly for recording several telephone conversations. A massive 1 inch reel of tape could record as many as 32 conversations for a complete 24 hour day. A time track enabled the searching of messages at some time during the day or night. But it did take some time to get from one end of the tape to the other. Then microprocessors took over the world and we tested endless updates of software. We tried recording multi track audio on Video tape but found that the tape decks kept failing. They were cheap enough but designed mainly to record or replay for 2 to 3 hours. We had slowed down the tape so it would last 24 hours! I did not question the Engineers at the time because they were never wrong! The final 'trick' was to use computer technology and did the recordings on hard drives. We could even record and replay at the same time! And any conversation was instantly recalled.
Black and white when I first saw one. It was in the 1970's that colour arrived. The picture was displayed on a cathode ray tube. (CRT). 405 lines created a moving picture at 25 frames a second. Just about enough detail to enjoy this new experience when I was a teenager. The BBC broadcast programmes in the afternoon and evenings with some 'interludes'. All live TV. Programmes could not be recorded then. Then one day Independent Tele Vision arrived. Television sets had to be redesigned to tune into two stations! A large knob was switched over with a loud click. The set had to be turned on before a programme started because it took time to 'warm up'. All valves then you see, not a transistor in sight. When transistors got invented the sound came on first.
Then BBC2 arrived. A major improvement with 625 lines making a much finer picture. The sound was improved as well being transmitted using FM. Very complicated multi format televisions with two tuners requiring two aerials! Still all black and white TV. I just cannot remember if BBC 2 was transmitting colour at that time. Eventually all TV transmissions were 625 line. The colour signal was cleverly mixed with the black and white one. Most TV's were still B/W and we all got those small neat TV aerials. I do remember seeing a colour TV in a shop window for sale at £250. Still only three stations to tune to and eventually all in colour. The next change was stereo sound using a system called 'nicam'.
Watching 'videos' at home became a reality when the video recorder was available to the mass market. By then most people had colour TV's and the recorder did colour as well. Only the posh ones did stereo sound. It was a very clever trick to record all the picture detail on a short piece of tape when you think of the problems with sound recording. A rotating head would swipe a track across the tape at an angle and at high speed while the tape moved slowly along. Each swipe was a complete picture so stopping the tape gave you a still picture. The sound was recorded along the edge of the tape. I think both were recorded using an FM signal to avoid interference. A noisy picture would not be tolerated.
I will not get too deep into these here. I just mention them because Micro Processors, very clever 'coding' and mathematics have enabled the DIGITAL revolution. Computers work very quickly on 'number crunching' using a binary code, 1's or 0's. All our natural analogue signals can be converted into digital and back into analogue. If you photo copy a picture several times the copy gradually looses its quality. Recording and replaying the digital code result in absolutely no loss in quality of the original analogue signal.
The Digital Revolution
Throw away all those tapes! And all those records. Here comes Compact Disks. CD's. The miracle of digitised sound. We got our first CD in 1990. Binary coded with extremely minute pits pressed into plastic representing the 1's and 0's by the billion. The digital information is picked up by light reflecting off the surface. Not any old light but a red laser from a new electrical device called a laser diode. The light is pure red of a very specific frequency able to see the pits pressed into the plastic.
Digital Versatile Disks came a bit later. DVD's. Note that the V was not for video. This Disk could contain enough data to play an entire film and more using a double layer.
Much more information is required for High Definition TV. The pits are so fine that a blue laser (Blue Ray) was needed which is light of much higher frequency than that of the red laser.
Digital is not new
Effectively like dots and dashes reminding me of that old Morse Code. The old fair ground organs used punched cards, holes or no holes, to play the music. Weaving machines used similar cards to define the pattern in carpet. Swiss music boxes used pins round a drum to pluck the tune.
Analogue to Digital Conversion
The signal is digitised by converting it into a long string of numbers. Each number represents the size of the signal at one point in time. The number of measurements you make depend upon how much detail you need to define it. High or low definition. The maximum frequency of sound is 20kHz. The best definition is achieved by taking 40 thousand measurements every second. Or twice the highest frequency of the signal. The numbers are actually binary 1's and 0's. In other words to the base 2. 'Normal' numbers are to the base 10.
Pictures are digitised using a code called Joint Photographic Expert Group. (JPEG) Movies are digitised using a code called Moving Picture Experts Group. (MPEG). Sound is digitised using MPEG - Audio Layer - 3. (MP3). But CD's used a different less compressed code. Compression of the code relies on the fact that much of the data is similar or just gaps in sound. Error Correction is built into the code. This means that if some data is missing the digital to analogue converter can 'repair' the signal up to a point. A badly scratched CD will result in gaps in sound. The errors in reception will show up on the TV as little square blocks spread all over picture. In the worst case the picture will just freeze.
Over the years the old analogue system had to cope with many changes and editions. From 405 lines to 625, from black and white to colour, from one channel to 5. When Channel 5 arrived the transmissions started to interfere with each other in some parts of the country. Then stereo sound was added as well ! There really was no room for more channels.
Radio and Television signals are now being transmitted using the digital code. High speed analogue to digital and digital to analogue converters are made possible by computer technology. This method of transmission is far more efficient than Analogue which it replaces. It requires far less 'bandwidth' so many more channels will fit in the same airspace.
Mix n Match?
In the beginning Radio, TV, Record players, Phones, Cameras, Computers, and any other electronic or electrical device you can think of was just that. We knew what they were for.
Seems any thing is possible, limited only by imagination and creativity.
Now it seems we can get a phone to take pictures but not a camera to make a call!
Cameras can take movies with sound but 'cine cameras' can't take pictures!
TV's can be connected to a phone so you can interact. Use it to order any product you see for sale. Do that with your computer as well.
Your kitchen could have a bar code reader and when you open a new packet of food the item could be added to a shopping list. This is sent to the shop and it gets delivered to your door. There was a time when the milkman delivered milk and the baker delivered bread. Now you can get the supermarket to deliver almost anything you need without leaving your living space!.
Chuck all the ingredients into a machine and out pops a cake or bread when it is cooked.
Computers can play music, display pictures, play movies, in fact do almost any thing the other devices can.
Seems that we are collecting little boxes. Video Cassette Recorders, Digital tuners, Satellite tuners, DVD players, CD players, Radio tuners, MP3 record players, Audio amps, Speakers. Many requiring a remote control as well! The TV is not just a TV. It can really be the Monitor into which you feed video and audio signals from all those little boxes. Interconnection becomes a bunch of wires all tangled up behind. Need some help here. 'SCART' connections help. But then there is also Audio/Video connections (AV), Camcorder (DV) etc. All using different forms of signal.
MY LITTLE BOOK OF ELECTRICKERY
Over the years I wrote these interesting facts and figures in my little black book.
Resistor Colour Code. (Which you should know by heart!)
I knew and used this for many years. It is used to mark the value of RESISTANCE on the resistor. 3 Bands of colour are used, the first 2 gives a number, the 3rd. is the multiplier or the number of 0's.. For Example 100 R = Brown Black Brown, 3400 R(3k4) = Orange Yellow Red. , 67000 R(67k) = Blue Violet Orange
Black = 0, Brown = 1, Red = 2, Orange = 3, Yellow = 4
Green = 5, Blue = 6, Violet = 7, Grey = 8, White = 9
1,000,000,000 = Giga(9)
1,000,000 = Mega(6)
0.001 = milli(-3)
0.000,001 = micro(-6)
0.000,000,001 = nano(-9)
0.000,000,000,001 = pico(-12)
Radio waves travel at the speed of light. 300,000,000 Meters / Second.
Frequency = Speed/Wavelength. Wavelength = Speed/Frequency.
Frequency Wavelength Band
300,000 MHz 0.1 cm EHF
30,000 MHz 1 cm EHF
3,000 MHz 10 cm SHF
1,400 MHz 21 cm Frequency of hydrogen atoms. Space noise.
1,000 MHz 0.30 m UHF
800 MHz 0.37 m UHF TV
400 MHz 0.75 m UHF TV
100 MHz 3 m VHF FM Radio (Audio frequency responce 50 Hz / 15 KHz).
80 MHz 3.75 m VHF FM Radio.
8,000 KHz 37.5 m HF Short Wave Radio.
1,000 KHz 300 m MF Medium Wave Radio (Audio frequency responce 100 Hz / 5 KHz)
200 KHz 1,500 m LF Long Wave Radio.
30 KHz 10 Km VLF.
20 KHz Hi Fi. High frequency.
18 KHz You may be able to hear this if youre very young, a cat or dog!
10 Khz Highest frequency you can get off cassette tape. Treble
4 KHz Sound of a Piccolo.
3 Khz Top frequency you get on the phone.
1 KHz Standard Audio Frequency (0 dBm). Mid range
880 Hz A Music.
440 Hz A Music.
100 Hz Bass Drum. Bass
50 Hz Hi Fi. Low frequency.
Audio (sound) Volume is measured in Decibels (dB).
1 dB is the smallest detectable change in volume. An increase of 10 dB doubles the sensation of sound.
0 dB Threshold of hearing. 10 dB Normal breathing. 20 dB Leaves rustling in breeze. 30 dB Empty Cinema. 40 dB Residential neighbourhood. 50 dB Quiet Restaurant. 60 dB Two person conversation. 70 dB Busy traffic. 80 dB Vacuum cleaner. 90 dB Niagara Falls. 100 dB Underground train. 120 dB Threshold of pain.
The EAR can detect a range of 120 dB. A CD has a dynamic range of 100 dB. A live orchestra produces a range of 70 dB. FM radio program has a dynamic range of 60 dB.
STANDARD METRIC UNITS
LENGTH: Metre m :- A length equal to 1,650,763.73 wavelengths of radiation from Krypton 86
MASS: Kilogram kg :- Is the weight of 1000 cc (litre) of water. 1 cc weighs 1 gram.
FORCE: Newton N :- Is the force required to give a mass of 1 Kilogram an acceleration of 1 m/s squared. (Kg m/s/s). (After the 1st second speed is 2 m/s). As gravity is about 10 m/s/s a Newton is about 100 grams.
HEAT: Joule J :- Calorific value given in MJ/Kg or MJ/m squared. Coal = 34, Natural Gas = 36, Butane Gas = 120.
ENERGY: A force of 1 Newton acting over a distance of 1 meter.
POWER: Watt W :- 1 W = 1 Joule / second. = Volts X Amps. 1 horsepower is 745.7 W (J/s)
CURRENT: Ampere A :- 1 Amp is said to be passing through two wires each 1 meter apart when the force between them is 2 X 10-7 Newtons.
TEMPERATURE: Centigrade :- 0 c Freezing water, 100 c Boiling water.
TEMPERATURE: Kelvin K :- Is based on Centigrade scale. 0 degrees K = -273.15 C. (At this temperature the atoms have stopped moving.)
LUMINOS: Candela cd :- 1 cd is the radiation given off 1/60 sq cm of rough black surface at the melting point of platinum.
A unique code for 16 different states using 4 data lines.
4 Bit Binary 8. 4. 2. 1.... Decimal.