Sine wave - nature's clock.
Waves in fluids : Sound, electro-magnetic (light, radio waves), ocean waves.
Physical movement : pendulums, springs.
Sine wave may loose power/amplitude when transmitted over distance,
but it won't distort unless influenced by an external force.
Technique : ASK (amplitude-shft keying) - Amplitude modulation (AM)
Embed the data in a carrier that provides a timing signal.
Vary amplitude to embed data.
For AM, Carrier frequency non-varying.
Bits represented by varying amplitude.
More useful for transmitting analog data.
More susceptible to interference.
Cost effective for voice but poor quality for music.
* walkie-talkies, short-wave radio.
Uses more power than other technologies.
Reception and demodulation devices cheaper than other technologies.
Short-wave is AM. Transmission distances of 1000's of miles.
Sometimes combined with other modulation methods to increase data density.
Technique : Frequency-shift keying (FSK) - Frequency modulation (FM)
Embed the data in a carrier that provides a timing signal.
Vary frequency to embed data.
Two frequencies (1 double the other) to represent 1 and 0.
More commonly offset on either side of a higher frequency carrier.
* More efficient, vary by a percentage either side of carrier frequency.
* 4 MHz main carrier, 3.8 MHz - zero, 4.2 MHz - one.
*
* 802.11n 300 Mbps transfer, 5.4 GHz
* 3x10^8 bits/sec on 5.4 * 10^9 cycles/sec
* Carrier almost 20X the data rate.
In practice, using signals that are whole modulus of each other can
induce harmonic distortion, so more commonly high frequency may be 2.3x
or some other odd partial multiplier.
Less susceptible to interference (noise).
Sinodal nature less susceptible to attenuation.
Data transmission over phone lines, modems, wireless broadcast.
Even DSL over copper phone lines uses an analog FM carrier.
DSL carrier signals > 25KHz.
Voice carrier signals 300 Hz - 3.4 KHz.
* Human hearing 12Hz - 20KHz. Ideal hearing.
FM in the audio frequency range was used in earliest modems and allowed
300 bits/s. A set of frequencies were picked that had least distortion
and were such that sending and receiving data didn't interfere with each
other.
Because most phone circuits were designed to handle a maximum of 3KHz.,
this also limited the baud rate.
***************************
From the movie "Almost Famous"
Ben Fong-Torres: "It's called a Mo-Jo, it's a very high-tech machine
that transmits pages over the telephone! It only takes eighteen minutes
a page!"
For AM, Carrier frequency non-varying.
Bits represented by varying amplitude.
More useful for transmitting analog data.
More susceptible to interference.
Cost effective for voice but poor quality for music.
* walkie-talkies, short-wave radio.
Uses more power than other technologies.
Reception and demodulation devices cheaper than other technologies.
Short-wave is AM. Transmission distances of 1000's of miles.
Sometimes combined with other modulation methods to increase data density.
Technique : Frequency-shift keying (FSK) - Frequency modulation (FM)
Embed the data in a carrier that provides a timing signal.
Vary frequency to embed data.
Two frequencies (1 double the other) to represent 1 and 0.
More commonly offset on either side of a higher frequency carrier.
* More efficient, vary by a percentage either side of carrier frequency.
* 4 MHz main carrier, 3.8 MHz - zero, 4.2 MHz - one.
*
* 802.11n 300 Mbps transfer, 5.4 GHz
* 3x10^8 bits/sec on 5.4 * 10^9 cycles/sec
* Carrier almost 20X the data rate.
In practice, using signals that are whole modulus of each other can
induce harmonic distortion, so more commonly high frequency may be 2.3x
or some other odd partial multiplier.
Less susceptible to interference (noise).
Sinodal nature less susceptible to attenuation.
Data transmission over phone lines, modems, wireless broadcast.
Even DSL over copper phone lines uses an analog FM carrier.
DSL carrier signals > 25KHz.
Voice carrier signals 300 Hz - 3.4 KHz.
* Human hearing 12Hz - 20KHz. Ideal hearing.
FM in the audio frequency range was used in earliest modems and allowed
300 bits/s. A set of frequencies were picked that had least distortion
and were such that sending and receiving data didn't interfere with each
other.
Because most phone circuits were designed to handle a maximum of 3KHz.,
this also limited the baud rate.
***************************
From the movie "Almost Famous"
Ben Fong-Torres: "It's called a Mo-Jo, it's a very high-tech machine
that transmits pages over the telephone! It only takes eighteen minutes
a page!"