Wireless Communication

Posted by PITHOCRATES - December 18th, 2013

Technology 101

When a Current passes through a Wire it creates an Electromagnetic Field around the Wire

Wireless communication.  A pretty amazing technology.  Allowing ships at sea for the first time in history to communicate with people on land.  While at sea.  Using Morse code.  Those dots and dashes that take a little translation to understand.  But we could translate anything we said into Morse code.  Most people may even know the universal distress signal.  SOS (· · · – – – · · ·).  Which sent ships racing to the ship in distress.  Instead of simply disappearing from the face of the earth.  Something we owe a deep gratitude for to Nikola Tesla.  Or Guglielmo Marconi.  Depending on which side you’re on in the great patent dispute.  Was Tesla first?  Or was Marconi?  Suffice it to say they were both great inventors.  And the world is a better place because of them.

Electromagnetic field and waves.  Fascinating technology.  But one that is a little difficult to understand.  Because they’re invisible.  You can’t see them.  But we can use them to do incredible things.  If you enjoy using a smartphone you can thank electromagnetic field and waves.  For this technology is what makes wireless communication work.

When a current passes through a wire it creates an electromagnetic field around the wire.  Which can induce a current in an adjacent wire.  This is how transformers work.  By electromagnetically coupling one circuit with another.  Wireless radio transmission is similar.  Only the two circuits are pretty far apart from each other.  Being far apart, though, requires a lot of power.  And the further apart the two circuits are the more power they require.

A Radio Transmitter takes the Source Signal and Modulates it on the Carrier Frequency

When you tune into your favorite radio station you’re tuning into the carrier frequency of that station.  Which is just a powerful sinusoidal wave at one frequency they pump out on an antenna.  If you listened to just this carrier frequency you would hear a single, constant tone.  Sort of like the sound you hear on the television when they show a test pattern.  It’s not interesting or entertaining.  But it is powerful.  And the antenna they broadcast on can create one powerful electromagnetic field.  Such that the antenna on any radio receiver in or near the same city that radio transmitter is in can tune into that frequency and ‘hear’ it.  Basically with a tuner that allows only the station frequency you want to hear to pass.  While blocking the myriad of other carrier frequencies in the atmosphere.

These two antennas are the two circuits electromagnetically coupled together.  The transmitter is basically sending a current into the transmitter antenna to ‘vibrate the air’ while the receiver antenna ‘picks up those vibrations’ and induces an electric current.  And the more powerful the transmitter the farther you could pick up those ‘vibrations’.  Ships at sea had powerful transmitters.  Powered by large generators driven by their powerful steam engines.  Which allowed these signals to travel from the middle of the Atlantic to a shore receiver.  But if you did not have access to a power source you could ‘plug into’ you greatly reduced the effective range.  Because you had to use batteries.  Walkie-talkies kids play with have a small battery.  So they can’t be too far from each other to talk to each other.  The first light-weight solid state radio the Army used—AN/PRC 77 (aka ‘prick-77’)—had a much greater range.  About 5 miles.  And a much, much heavier battery.  It was so heavy that soldiers wore it like a backpack.  Which was another reason to not want to carry it.  The other being that the enemy tried to shoot the people with the radio.

Of course, these radios just didn’t transmit those carrier frequencies.  For that wouldn’t be any fun for kids.  Or useful for soldiers in combat.  And it’s just not pretty music.  No, it’s what we ‘add to’ the carrier frequency that is fun, useful and pretty.  A radio transmitter takes the source signal (voice, music, data, etc.) and modulates it on the carrier frequency.  To better understand what this means without any technical explanation listen to the Rod Stewart song Mandolin Wind.  After he sings, “I don’t have much.  But what I’ve got is yours.  Except, of course, my steel guitar.  Ha, ’cause I know you don’t play.  But I’ll teach you one day.  Because I love ya” there is a brief steel guitar solo (starting at 2:36 on the above link).  It’s a rapid picking of strings as he slowly fingers different frets.  Changing the frequency of the rapidly picked strings.  Reproducing the ‘slower’ melody on the ‘faster’ vibrating strings.  This is basically what modulation is.  Imprinting a low-power signal (voice, music, data, etc.) onto a high-power signal (a carrier frequency).  The receiver then demodulates the original signal from the carrier wave.  So we can hear or use it.

Having Cellular Towers all over the place Greatly Reduces the Amount of Power our Mobile Devices Need

The AN/PRC 77 and walkie-talkies are half-duplex devices.  They use the same carrier frequency to transmit and receive.  So only one person can talk at a time.  Which required people to say ‘over’ when they finished what they were saying to let the other person know they could start talking.  When the person said all he or she was going to say they said ‘out’ to let the other person know they were done with this communication (they NEVER said ‘over and out’.  That was only in movies with poor military consultants).  It was a great system.  Far better than earlier battlefield communications.  Such as the telegraph.  Or the messenger.  It changed the way we fought wars.  But it didn’t translate well to cellular phones.  Because this isn’t the way we talk in social situations.

Also, people just aren’t going to throw something heavy like an AN/PRC 77 on their back when they leave the house.  For the thing weighed nearly 14 pounds.  Because of the batteries.  And what would this funny way of talking and this heavy weight give you?  The ability to talk to someone 5 miles away.  There’s a reason why people don’t use these half-duplex devices for our mobile telephones.  Because there’s something better.  Cellular technology.  Where they made the use of mobile devises more user-friendly by greatly expanding the cellular infrastructure.  That thing our mobile devices talk to.  Instead of requiring a powerful transmitter and receiver (and a large antenna) in our mobile phones we built cellular towers all over the place.  So we are no further than 5 miles (approximately) from a cellular tower.  Which is all the distance our wireless signal needs to travel.  For once it reached a tower your call switched over to the landline system.  And could reach anyplace in the world.  Even to another mobile device.  As long as it is within 5 miles (approximately) of another cellular tower.

Having cellular towers all over the place greatly reduces the amount of power our mobile devices need.  Allowing a small and very light battery to power them.  Making these mobile devices very light weight.  In fact, the batteries are so light that these devices can transmit and receive on two carrier frequencies.  Allowing full-duplex communication.  Where both people can talk at the same time.  Just like in casual conversation.  They are so user friendly and convenient that today many people use their mobile phone far more than any landline telephone.  Something that would no doubt bring great satisfaction to Nikola Tesla and Guglielmo Marconi if they were alive today.  Who have given us the gift of wireless communication.  Well, at least one of them.



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Music, Radio Transmitters, Radio Receivers, CD Players, Compression, MP3 Players, Internet, YouTube, Live Streaming and Music on Demand

Posted by PITHOCRATES - February 29th, 2012

Technology 101

The Roaring Twenties brought Electrical Power and Broadcast Radio into our Homes

We take music for granted today.  We can listen to pretty much anything we want to.  At any time.  In any place.  In the home.  In the car.  At the gym.  It’s nice.  You can listen to some of the most beautiful music at your convenience and leisure.  It wasn’t always like this, though.  During the time Edvard Grieg composed his masterpieces few could listen to them.  Unless you attended a live performance.  Which weren’t that readily available.  Unless you lived in a big city.  Where a symphony orchestra could include some of his music in a performance.  But you had to listen to what they played.  And what they played was the only music you were familiar with.  Unless you had a friend with a piano.  Who could read sheet music.  And was a concert-level pianist.  Again, something not that common.

But today you can click on a computer link and listen to almost any obscure piece of music there is.  From Grieg’s beautiful Bådnlåt (At the Cradle), lyric piece for piano, Op. 68/5.  To something really esoteric like Sparks’ As I Sit Down To Play The Organ At The Notre Dame Cathedral.  You can listen to them.  You can buy them.  Download them to a portable MP3 player.  And take them anywhere.  Just imagine trying to do this in 1899.  Going to the lake.  And wanting to listen to Grieg’s new lyric piece for piano.  Opus 68.  Number 5.  At the Cradle.  Unless you took a piano and a concert-level pianist with you that just wasn’t going to happen.  But this all changed.  Beginning around the dawn of the 20th century.

Nikola Tesla had recently won his war with Thomas Edison.  His AC power replaced Edison’s DC power as the standard.  And in the 1920s we were electrifying the country.  We began to generate and transmit AC power across the land.  To businesses.  And to homes.  Where we could plug in the new electrical appliances coming to market.  We were working on another new technology during this time.  Something that could plug in at home to the new electrical power.  The radio.  This technology had something to do with electromagnetic fields and waves.  Transmitted between antennas.  One on a transmitter.  And one on a receiver.  As long as the transmitter and the receiver were tuned to the same frequency.  The first use of this new technology was in the form of a wireless telegraph.  Which few people had in their homes.  These were more useful to communicate with others who were not connected by telegraph lines.  Like ships at sea.  Where we sent Morse code (those dots and dashes that spelled words).  Which worked well.  As long as all the ships didn’t tried to communicate at the same time on the same frequency.  But transmitting speech or music was a different manner.  Because everyone talks more or less in the same band of frequencies.  And notes played on one violin tend to play at the same frequency on another violin.  So if some radio transmitters broadcasted different concerts at the same time you wouldn’t hear a nice concert on your radio.  You’d hear a cacophony of noise.  To get an idea what that would sound like open up three or four browser windows on your computer.  And play a different song on YouTube in each.  What you hear will not be music.  But noise.

In the Eighties we traded our Phonograph Needles for Laser Beams in our CD Players

Of course, this didn’t stop the development of commercial broadcast radio.  For we tune radio transmitters and radio receivers to the same resonant frequency.  The transmitter transmitting at one frequency all of the time. While the radio receiver could tune in to different frequencies to listen to different radio broadcasts.  When you turned the radio tuning dial you changed what resonant frequency your receiver ‘listened’ to.  Which was basically a filter to block all frequencies but the tuned frequency from entering your radio.  We call that frequency the carrier signal.  Typically just a plain old sinusoidal wave form at a one frequency that we imprint the information of the speech or music on.  The transmitter takes the music waveform and modulates it on the carrier signal.  Then broadcasts the signal on the broadcast antenna.  The receiver then captures this signal on its antenna.  And demodulates it.  Pulling the musical imprint from the carrier signal.  And restoring it to its original condition.  Which the radio than amplifies and sends to a speaker.  I left some steps out of the process.  But you get the gist.  The key to successful broadcast radio was the ability to transform the source signal (speech or music) into another signal.  One that we could transmit and receive.  And transform back into the source signal.

The Roaring Twenties was a Neil Armstrong moment on earth.  It was one giant leap for mankind.  For it was in this decade that the modern world began.  Thanks to Nikola Tesla and his AC power.  Which allowed us the ability to plug in radios in our homes.  And power the great radio transmitters to get the signal to our houses.  Tesla, incidentally, created radio technology, too.  Well, Tesla, and Guglielmo Marconi.  (Patent disputes flared between these two greats about who was first.)  Great technological advancement.  Created during a time of limited government and low taxes.  That unleashed an explosive amount of creativity and invention.  The Eighties was another such decade.

The Eighties launched the digital age.  The world of bits and bytes.  1s and 0s.  Digital watches.  Clocks.  Calculators.  PCs.  And, of course, our music.  For the Eighties gave us the compact disc.  The CD.  Music that didn’t wear out like our vinyl records.  And didn’t pop or hiss with age.  Because a CD player didn’t have a phonograph needle.  That rode the groves on our vinyl records.  It had something far more futuristic.  A laser beam.  That reads information encoded into the CD.  Information encoded onto a reflective layer through a series of pits.  During playback the laser either reflects or doesn’t reflect.  This information is than processed into a series of 1s and 0s.  Then converted into the analog waveform of the source material.  And becomes music again.

The Eighties gave us the Digital Age which led to the Internet and Music on Demand

This process is similar to the process of broadcast radio.  Not in any technological way.  But by changing a source signal into something else.  And then converting it back again.  In the case of the CD we sample an analog signal (i.e., an audio recording).  By taking ‘snapshots’ of it at regular intervals.  Then convert these snapshots into a digital format.  And then transfer this digital information to the reflective layer on a CD.  Those 1s and 0s.  When we play it back the laser reads these 1s and 0s.  Then converts these digital snapshots back into the original audio signal.  Sort of like modulating and demodulating a signal.  Only instead of modulating we’re converting from analog to digital.  Then vice versa.

The quality of the digital format depends on how much information each snapshot contains.  And the interval we sample them at.  Larger chunks of information taken in short intervals contain a lot more information.  And improve the quality of the sound.  But it will also take up a lot of space on those CDs.  Limiting the number of songs we can encode on them.  Which lead to compression.  And MP3s.  Which worked on the premise that there’s a lot of music in music.  But we don’t necessarily hear all of that music.  Some sounds mask out other sounds.  Certain frequencies we barely hear.  So while the CDs tried to reproduce the music as faithfully as possible, we learned that we could discard some of the information in the music without reducing the quality of the music much.  This saved a lot of space on CDs and portable MP3 players.  Allowed faster downloads on the Internet.  And live streaming.

The Roaring Twenties changed our world.  Modernized it.  And gave us many things.  Including broadcast radio.  And music in our homes we never had before.  And the Eighties also changed our world.  Further modernizing it.  Giving us the digital age.  That led to the Internet.  And music on demand like we never had before.  Where we can listen to anything.  No matter how obscure.  It’s now all available at our fingertips.  To listen online.  Or to buy and download to a portable device.  From Grieg to Sparks.  And everything in between.



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