Hello All, its the 27th of Oct. 2014
We discussed receivers. A bit on transmitters with vacuum tubes. But before we proceed, we have to covered two topics. Electromagnetic waves(EMW) and modulation.
EMW
Also called radio waves. It is a sine wave which goes positive then negative in one cycle. With tubes, it became possible to build oscillators and with crystals, it became possible to create an oscillator with a fixed frequency. Tubes not only created oscillators but also served to amplify the signal.
The TX coil is like a primary coil in a transformer. The oscillator creates how many cycles are generated in a second. Our wall AC supply for example has an oscillation of 60 Hertz, very low and hardly at radio waves frequency. The MW broadcast band ,AM, is around 1 Mhz. The CB radio is at 27Mhz. Today the new band is at 2.4 Gigahertz.
The receiver coil is like a secondary coil in a transformer. So, what the TX generates, the RX can still pick it up at great distances but in a very minute form, in microvolts. In a transformer, the coils are not in resonance and current is induced to the secondary via the metal core. In radio, there is no core but space. The coil being in resonance permits the RX coil to "hear" at great distances.
Sunday, October 26, 2014
Tuesday, October 21, 2014
It's Wed, 10-22-14. I don't know if my computer calendar has adjusted. Good Morning to All.
Our last topic was radios in the 30's and 40's. The first radios were using earphones, then speakers. The dominant design then was the direct conversion receiver, the signal was rectified then fed to an amplifier. Then Armstrong discovered a way to improve reception and his designed became popular for quite sometime. he introduced the Reflex radio circuit wherein the signal is fed back into an earlier stage as to cause an oscillation at a frequency. There a knob to adjust the feedback to a ax point. Reception dramatically improved when someone not only amplified the RF signal before detection but but also greatly improved selectivity, keeping s station tuned and rejection neighboring channels. This technique was mixing the incoming frequency with a locally produced signal. Then the differential signal was sent to s series of tuned amplifiers, before detection. The result was amazing. No more fussing of the feedback knob. This design was called the superheterodyne system. Superhet for short.
Our last topic was radios in the 30's and 40's. The first radios were using earphones, then speakers. The dominant design then was the direct conversion receiver, the signal was rectified then fed to an amplifier. Then Armstrong discovered a way to improve reception and his designed became popular for quite sometime. he introduced the Reflex radio circuit wherein the signal is fed back into an earlier stage as to cause an oscillation at a frequency. There a knob to adjust the feedback to a ax point. Reception dramatically improved when someone not only amplified the RF signal before detection but but also greatly improved selectivity, keeping s station tuned and rejection neighboring channels. This technique was mixing the incoming frequency with a locally produced signal. Then the differential signal was sent to s series of tuned amplifiers, before detection. The result was amazing. No more fussing of the feedback knob. This design was called the superheterodyne system. Superhet for short.
Monday, October 20, 2014
Hi October 21, 2014. How time flies even tho it has no wings.
Good Morning.
We were discussing the Sprtk Gap and the great innovation in the receiver section with the intro o f the galena diode(actually a Schottsky!) and vacuum tubes. A bit on vacuum tubes or valves as the British called them. Credit should really be given to Edison. He invented the light bulb and the vac tube came about with experiments on his vac lights. Names like Fleming, De Forest, etc were associated with the vac tubes.
In the beginning, there was only the light bulb. A filament inside a vacuum which lighted up and did not burn up since there was no oxygen. A second element was placed inside and when a battery with voltages in the 45 V range was place across the lighted filament and the second element, lo and behold, current was transferring from the filament to the second element to be later called the Plate. This was the diode! And better thna the galena crystal. so, tubes were first used as diodes to convert AC RF to DC. A mid element was then place in between the filament and the Plate. Plus was on the Plate. It was called the Grid. It was discovered that when the Grid was given a very tiny plus current, it speed up the rush of current from the filament, to be later called the Cathode, to the Plate. Eventually, the Cathode was a separate element around the filament which heated up with no physical contact to one another. This was the TRIODE! And this was the first AMP. A tiny signal can control a stronger flow of current. There was an explosion of radio tubes in the 30's and 40's. Five tube table radio receivers became a household item and soon the hi fi's were in vogue. Two way radios became realities in WW2 which also saw the use of valves to control rockets built in Germany. But the tubes were bulky, fragile and heated up. They consume lots of power. In the late 1940's, the Americans discovered transistors. By the 1950's, small pocket radios started to appear using no more than 4 cells or a 9V battery. Sony Corp was in fact at the forefront selling its pocket radio. The transistor was a 3 element device using germanium. Bell Labs started with PNP's. The emitter goes to ground, thus most of the Japanese radios were PNP radios using Germanium transistors with the suffix 2SA for RF trannies and 2SB for audio trannies. For higher current trannies, the 2SC and the 2SB trannies appeared which were now NPN'c and Silicon. Silicon is cheaper and soon, trannies were plentiful and cheap.
Good Morning.
We were discussing the Sprtk Gap and the great innovation in the receiver section with the intro o f the galena diode(actually a Schottsky!) and vacuum tubes. A bit on vacuum tubes or valves as the British called them. Credit should really be given to Edison. He invented the light bulb and the vac tube came about with experiments on his vac lights. Names like Fleming, De Forest, etc were associated with the vac tubes.
In the beginning, there was only the light bulb. A filament inside a vacuum which lighted up and did not burn up since there was no oxygen. A second element was placed inside and when a battery with voltages in the 45 V range was place across the lighted filament and the second element, lo and behold, current was transferring from the filament to the second element to be later called the Plate. This was the diode! And better thna the galena crystal. so, tubes were first used as diodes to convert AC RF to DC. A mid element was then place in between the filament and the Plate. Plus was on the Plate. It was called the Grid. It was discovered that when the Grid was given a very tiny plus current, it speed up the rush of current from the filament, to be later called the Cathode, to the Plate. Eventually, the Cathode was a separate element around the filament which heated up with no physical contact to one another. This was the TRIODE! And this was the first AMP. A tiny signal can control a stronger flow of current. There was an explosion of radio tubes in the 30's and 40's. Five tube table radio receivers became a household item and soon the hi fi's were in vogue. Two way radios became realities in WW2 which also saw the use of valves to control rockets built in Germany. But the tubes were bulky, fragile and heated up. They consume lots of power. In the late 1940's, the Americans discovered transistors. By the 1950's, small pocket radios started to appear using no more than 4 cells or a 9V battery. Sony Corp was in fact at the forefront selling its pocket radio. The transistor was a 3 element device using germanium. Bell Labs started with PNP's. The emitter goes to ground, thus most of the Japanese radios were PNP radios using Germanium transistors with the suffix 2SA for RF trannies and 2SB for audio trannies. For higher current trannies, the 2SC and the 2SB trannies appeared which were now NPN'c and Silicon. Silicon is cheaper and soon, trannies were plentiful and cheap.
Tuesday, October 14, 2014
Hi, it is Wed morning. To continue, for a while, Spark Gaps were used but at the receiver, the diode detected the signal. Morse was used. By the 20th century, the vacuum tube arrived. Thnks to Edison for inventing the light bul which led to vacuum tubes. Receivers were built with vacuum tubes which has improved receiving tremendously. Then came the new transmitters. Vacuum tubes and no more huge sparks.
REFLECTION
The transmitter and receiver were like a transformer. The Tx was the primary P and the RX was the secondary S. It was air cored and the P and S were at great distances. Any current induced in P will create a magnetic field around the coil and will radiate Electro Magnetic Waves. The S will sense the EMW and will absorb some energy from it. The further the S , the weaker the sensed current..
The concept of the oscillator was born. To produce sine waves, a coil is paralleled to a condenser. A vacuum tube was used to continously pump current into this pair called a TANK CIRCUIT. The tank circuit has a unque behaviour in that the coil stores energy and transfers it to the capacitor. The capacitor then discharges into the coil. If not for the vacuum tube, the oscillation will decay. Evenrtually,semiconductors or transistors took over the job of the vacuum tubes. The tube/transistor has basically three elements where one element can control the flow of current in the other two elements.This characteristic allows the oscillation to keep re triggering the tube/transistor. Our first project is to demonstrate this oscillator.
REFLECTION
The transmitter and receiver were like a transformer. The Tx was the primary P and the RX was the secondary S. It was air cored and the P and S were at great distances. Any current induced in P will create a magnetic field around the coil and will radiate Electro Magnetic Waves. The S will sense the EMW and will absorb some energy from it. The further the S , the weaker the sensed current..
The concept of the oscillator was born. To produce sine waves, a coil is paralleled to a condenser. A vacuum tube was used to continously pump current into this pair called a TANK CIRCUIT. The tank circuit has a unque behaviour in that the coil stores energy and transfers it to the capacitor. The capacitor then discharges into the coil. If not for the vacuum tube, the oscillation will decay. Evenrtually,semiconductors or transistors took over the job of the vacuum tubes. The tube/transistor has basically three elements where one element can control the flow of current in the other two elements.This characteristic allows the oscillation to keep re triggering the tube/transistor. Our first project is to demonstrate this oscillator.
Monday, October 13, 2014
Good Morning. It is Tuesday Morning, Oct. 14, 2014
Well, I discussed waves and resonance. Human ears can hear up to the khz range only. electrical waves came to be know as Electro Magnetic Waves. We all know that magnetism and electricity are inter-related.
magnets can generate electricity and vice versa.
A bit of history. Man was amazed by lightning but in the old days, didn't really understand it, much less harness it. In the 19th century, Man began creating mini lightnings in the form of sparks. A spark sent out waves of different frequencies. It was like a shotgun. It was discovered that these waves were also magnetic. Iron fillings inside a glass tube aligned and freeze up in the presence of these waves. The transmitter was called the SPARK GAP and the Receiver was called the COHERER TUBE. Since the fillings lined up and made contact with one another, electrical conduction took place. The first transmitter and the first receiver were conceptualized and were actually made. A man actually controlled a floating balloon inside a theatre controlled by these TX and RX! Single channel and very broadband. From 1886 to 1916, telegraphs used Spark Gap transmitters. Marconi used this type of transmitter to send a telegraph message across the Atlantic.
Then the Galena crystal! The Galena Crystal was the first semiconductor device. It was a Schottky Hot Carrier Diode! It converted the Alternating RF current to Pulsing DC, pulsing based on the modulation at the TX.
Well, I discussed waves and resonance. Human ears can hear up to the khz range only. electrical waves came to be know as Electro Magnetic Waves. We all know that magnetism and electricity are inter-related.
magnets can generate electricity and vice versa.
A bit of history. Man was amazed by lightning but in the old days, didn't really understand it, much less harness it. In the 19th century, Man began creating mini lightnings in the form of sparks. A spark sent out waves of different frequencies. It was like a shotgun. It was discovered that these waves were also magnetic. Iron fillings inside a glass tube aligned and freeze up in the presence of these waves. The transmitter was called the SPARK GAP and the Receiver was called the COHERER TUBE. Since the fillings lined up and made contact with one another, electrical conduction took place. The first transmitter and the first receiver were conceptualized and were actually made. A man actually controlled a floating balloon inside a theatre controlled by these TX and RX! Single channel and very broadband. From 1886 to 1916, telegraphs used Spark Gap transmitters. Marconi used this type of transmitter to send a telegraph message across the Atlantic.
Then the Galena crystal! The Galena Crystal was the first semiconductor device. It was a Schottky Hot Carrier Diode! It converted the Alternating RF current to Pulsing DC, pulsing based on the modulation at the TX.
Sunday, October 12, 2014
Oct. 13, 2014
Hi good afternoon.
Theoretical physicists are now saying that different matters in the universe are just waves, waves of different frequencies. The universe is alive with oscillations. If you look at the wave spectrum or frequency spectrum, we can go down to one kilohertz and even lower and the upper end are gamma rays. It between are sound waves, radio waves, light waves, x rays etc. Light waves are waves visible to our eyes. But we cannot see radio waves. We can feel some waves, the heat waves. There is one light wave that we cannot see:infrared.
When we drop a pebble in a lake, the waves travel outward in ripples. Waves travel and therefore, it must have speed. Radio waves and Light waves travel at 300 Million meters per second or at 300 x 10 to the 6. It takes the light from the sun 8 seconds to reach earth. All images in the sky took years traveling at the speed of light to reach our eyes.
WAVES VARY IN LENGTH
Waves have lengths and is called wavelengths. The wavelength is inversely proportional to its frequency.
When we say 2 Meter band, the WL is 2 meters.What is the frequency. Well, it is easier to view it this way. If the wave traveled 300 M meters in one second, and the wavelength is 2 meters, there are 300M meters/2 repetitions as it travels in one second. Thre frequency therefore is 150 million hertz or 150 Mhz. so, the formula is:
WL=300 M/ Freq. in Mega hertz. Thus at a frequency of 150 Mhz, it is 300 M/150 Mhz= 2 meters.
Look at the waves as a crawling caterpillar on a long stick. The caterpillar arches like a letter S and the distance its body covers is the WL. The shorter it is, the more cycles it has to make to cover a distance. A radio wave is a sine
Let us go to reality. The MW BC band in AM is around 1 Mhz in the middle (.640-1.640Mhz). What is the meter band for this band? It is 300/1 or 300 meter band. in the shortwave band, at 7.7Mhz, what is the WL? It is 300/7.5=40 Meter. The CB band is 11 meters (300/27). The FM band is around 3 Meter at 100 Mhz. As we go higher into the UHF band like the 430 Mhz for amateurs, the WL is about .7 meters. our cellphones are at 900 Megs, 1.8 Gigahertz and other services today are at 2.4 Gigahertz. They are in the microwave region.
Hi good afternoon.
Theoretical physicists are now saying that different matters in the universe are just waves, waves of different frequencies. The universe is alive with oscillations. If you look at the wave spectrum or frequency spectrum, we can go down to one kilohertz and even lower and the upper end are gamma rays. It between are sound waves, radio waves, light waves, x rays etc. Light waves are waves visible to our eyes. But we cannot see radio waves. We can feel some waves, the heat waves. There is one light wave that we cannot see:infrared.
When we drop a pebble in a lake, the waves travel outward in ripples. Waves travel and therefore, it must have speed. Radio waves and Light waves travel at 300 Million meters per second or at 300 x 10 to the 6. It takes the light from the sun 8 seconds to reach earth. All images in the sky took years traveling at the speed of light to reach our eyes.
WAVES VARY IN LENGTH
Waves have lengths and is called wavelengths. The wavelength is inversely proportional to its frequency.
When we say 2 Meter band, the WL is 2 meters.What is the frequency. Well, it is easier to view it this way. If the wave traveled 300 M meters in one second, and the wavelength is 2 meters, there are 300M meters/2 repetitions as it travels in one second. Thre frequency therefore is 150 million hertz or 150 Mhz. so, the formula is:
WL=300 M/ Freq. in Mega hertz. Thus at a frequency of 150 Mhz, it is 300 M/150 Mhz= 2 meters.
Look at the waves as a crawling caterpillar on a long stick. The caterpillar arches like a letter S and the distance its body covers is the WL. The shorter it is, the more cycles it has to make to cover a distance. A radio wave is a sine
Let us go to reality. The MW BC band in AM is around 1 Mhz in the middle (.640-1.640Mhz). What is the meter band for this band? It is 300/1 or 300 meter band. in the shortwave band, at 7.7Mhz, what is the WL? It is 300/7.5=40 Meter. The CB band is 11 meters (300/27). The FM band is around 3 Meter at 100 Mhz. As we go higher into the UHF band like the 430 Mhz for amateurs, the WL is about .7 meters. our cellphones are at 900 Megs, 1.8 Gigahertz and other services today are at 2.4 Gigahertz. They are in the microwave region.
Good Morning to all, it is Monday morning 10-13-14.
I will discuss today RESONANCE. Two objects are in resonance when one responds to the vibration of the other. One example is the guitar. The "box" is designed to resonate with the strings. A better example is demonstrating that one tuning fork banged will make a similar tuning fork vibrate nearby such as in a quiet gym. So far, we have discussed resonance of physical objects.
Radio waves at a certain frequency will be detected by a receiver in resonance with it. The transmitter has an oscillating coil and the receiver has a similar receiving coil. When these two coils are in resonance, the receiver reacts to the presence of the transmitter.
So, when you get a pair of similar coils and use one in a TX and another in an RX, you can communicate using radio waves.
I will discuss today RESONANCE. Two objects are in resonance when one responds to the vibration of the other. One example is the guitar. The "box" is designed to resonate with the strings. A better example is demonstrating that one tuning fork banged will make a similar tuning fork vibrate nearby such as in a quiet gym. So far, we have discussed resonance of physical objects.
Radio waves at a certain frequency will be detected by a receiver in resonance with it. The transmitter has an oscillating coil and the receiver has a similar receiving coil. When these two coils are in resonance, the receiver reacts to the presence of the transmitter.
So, when you get a pair of similar coils and use one in a TX and another in an RX, you can communicate using radio waves.
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