Post on 26-Dec-2015
transcript
MComm Ch1 - 1
Chapter 1Chapter 1
Radio History and Communications
Elements
Transmitter
Source
Modulator
Destination
Demodulator
Receiver
MComm Ch1 - 2
OverviewOverview
• History
• Basic Communications System
• Simplex vs Duplex
• Basic Transmitter
• Decibels
• Basic Receiver
• Summary
>>
MComm Ch1 - 3
HistoryHistory
• Heinrich Hertz - 1st to produce radio waves
• Nikola Tesla – alternating current power
• Guglielmo Marconi - 1901 transmitted (one way) from United Kingdom to Newfoundland
• Reginald Fessenden – 1906 communications (both ways) between Scotland and Massachusetts
Hertz
1857-1894Tesla
1856-1943
Marconi
1874-1937Fessenden
1866-1932
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MComm Ch1 - 4
First Emergency UseFirst Emergency Use14 April 1912 from R.M.S. Titanic
1891-1956 1887-1912>>
MComm Ch1 - 5
TimelineTimeline
• Originally Continuous Wave (CW) in 1901 Morse Code
• 1st Amplitude Modulation (AM) 24 Dec 1906 by Reginald Fessenden from Brant Rock, MA
• Frequency Modulation (FM) patented in 1933 by Edwin Armstrong
• In 1943 Tesla named as inventor of radio by United States Supreme Court
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MComm Ch1 - 6
Basic Comm SystemsBasic Comm Systems
• Voice communications over short distances Transmission channel is sound wave
• Telephones over long distances Traditionally connected by metallic wires
• Radio communications over long distances Transmission channel is a radio frequency wave Interconnection requires
Common frequency Common modulation scheme
Sender ReceiverTransmission
Channel
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MComm Ch1 - 7
Comm System ElementsComm System Elements
Transmitter
Source
Modulator
Destination
Demodulator
ReceiverCommunications
Channel
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MComm Ch1 - 8
Simplex Vs. DuplexSimplex Vs. Duplex
• Simplex communications
• (Full) Duplex communications
• Half-Duplex communications
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MComm Ch1 - 9
Simplex CommunicationsSimplex Communications
• Transmitter and Receiver(s) on same frequency
• Transmitter converts sender’s voice to modulated RF
• Receiver converts modulated RF back to speech
Transmitter ReceiverRF Freq 1
Receiver(s)
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MComm Ch1 - 10
(Full) Duplex Communications
(Full) Duplex Communications
• Both can talk and listen at same time• Requires two frequencies
Transmitter ReceiverRF Freq 1
Receiver TransmitterRF Freq 2
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MComm Ch1 - 11
Half-Duplex Communications
Half-Duplex Communications
• Either talk or listen• Requires only one frequency
and Push to Talk (PTT) switch
Receiver Transmitter
PTT switch
Transmitter ReceiverRF Freq 1
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MComm Ch1 - 12
Basic TransmitterBasic Transmitter
Audio – 300 to 3,000 HzDC – 12 to 14 VDC
TransmitterAudio
DC
RF
Heat
RF
Heat – just a few watts
Chapter 3 will look inside the VHF-FM transmitter
Chapter 7 will look inside the MF/HF SSB transmitter>>
MComm Ch1 - 13
DecibelsDecibels• Unit used to compare two power
levels• Equation dB = 10 log P1/P2
• Important ratios Twice the power is +3 dB Ten times the power is +10 dB Half the power is -3 dB One-tenth the power is -10 dB
• What is approx ratio between 1 watt & 25 watts? Answer – slightly over 13 dB
1 to 10 is 10 db, 10 to 20 is 3 more dB>>
MComm Ch1 - 14
Basic ReceiverBasic Receiver
RF DC – 12 to 14 VDC
ReceiverAudio
HeatRF
DC
Audio – 300 to 3,000 Hz
Heat – just a few watts
Chapter 3 will look inside the VHF-FM receiver
Chapter 7 will look inside the MF/HF SSB receiver
>>
MComm Ch1 - 15
SummarySummary
• 1st emergency use of radio 1912 from Titanic
• Half Duplex used by VHF-FM One shared frequency
Either talk or listen Push-to-Talk
Say “Over” when you want the other party to talk
• Decibels are used to compare power levels Twice the power is +3 db One tenth is -10 db
>>