1. Radio History and Communications Elements
Chapter 1
Radio History and Communications Elements
Transmitter
Source
Modulator
Destination
Demodulator
Receiver
PowerPoint slides by
Stf/C Harl Porter, SN
Marine Electronics
Rear Commander for Electro-Mechanical Systems is
R/C Gene Danko, SN
Left is picture of Nikola Tesla, inventor of radio

2. Overview History Basic Communications System Simplex vs Duplex
Basic Transmitter
Decibels
Basic Receiver
Summary
Major sections in this chapter
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3. History Heinrich Hertz - 1st to produce radio waves
Nikola Tesla – alternating current power
Guglielmo Marconi transmitted (one way) from United Kingdom to Newfoundland
Reginald Fessenden – 1906 communications (both ways) between Scotland and Massachusetts
Hertz
Tesla
Marconi
Fessenden
Details in text first paragraph of History
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4. First Emergency Use 14 April 1912 from R.M.S. Titanic 1891-1956
R.M.S. stands for Royal Mail Ship
Upper left – Picture of Titanic Radio Room by Fr. Browne (who disembarked in Queenstown), probably of Harold Bride
5 KW rotary spark transmitter
4 wire antenna, between masts
Lower left – Harold Bride, 2nd Radio Operator age 21
Died in Scotland in 1956
Lower center – John G. Phillips, Chief Radio Officer, age 25
Died of hypothermia near lifeboat B, body never recovered
Upper right - Movie Set from James Cameron’s Titanic
Lower right – from Titanic movie
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5. Timeline 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
First one way transatlantic communications was in 1901
Fessenden also invented Depth Sounders
No formal education in electricity
Once worked for Thomas Edison
Armstrong’s also “invented” the super regenerative receiver while in school
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6. Basic Comm Systems Sender Receiver
Transmission
Channel
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
Three parts of a Basic Communications System:
Sender
Transmission Channel
Receiver
Transmission channels for phones today is a a combination of metallic wires, microwave systems and fiber optic cables. Cell phones and some cordless phones also use radio frequencies.
Radio communications can be half-way around the world or between earth and space
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7. Comm System Elements Source Destination Demodulator Modulator Receiver
Looking one level inside the Basic Comm system.
Source is the Sender from the previous diagram. Modulator and transmitter place the information on the communications channel.
Destination is the Receiver from the previous diagram.
Receiver and Demodulator extract the information from the communications channel.
Transmission Channel has been replaced by Communications Channel.
Communications
Channel
Transmitter
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8. Simplex Vs. Duplex Simplex communications (Full) Duplex communications
Half-Duplex communications
Sub-Topics in this section
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9. Simplex Communications
Transmitter
Receiver
Receiver(s)
RF Freq 1
Transmitter and Receiver(s) on same frequency
Transmitter converts sender’s voice to modulated RF
Receiver converts modulated RF back to speech
Top level depiction of Simplex Communications.
One way communications are from origin (source) to destination (sink), with no feedback.
Only one frequency is required. Single transmitter can broadcast to one or many receivers.
Examples are broadcast radio and TV.
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10. (Full) Duplex Communications
Transmitter
Receiver
RF Freq 1
Receiver
Transmitter
RF Freq 2
As suggested by slide title, Duplex Communications are sometimes called Full Duplex Communications. There are also Half-Duplex Communications, which are covered next.
Two frequencies are required and both parties can talk and listen at the same time. Normally the two frequencies are located fairly close to each other.
Both can talk and listen at same time
Requires two frequencies
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11. Half-Duplex Communications
Transmitter
Receiver
RF Freq 1
Receiver
Transmitter
PTT switch
Half-Duplex Communications requires only one frequency. Either party can talk or listen, but not at the same time. Use the Push-to-Talk switch and “over” to communicate.
In receive mode, the antenna is connected to the receiver input, the transmitter is disabled and the receiver is enabled.
When the transmitter is “keyed,” the antenna is switched to the transmitter output, the transmitter is enabled (keyed) and the receiver is disabled. The PTT switch above only illustrates the switching of the antenna.
The big advantage of half duplex, over full duplex, is that it requires only one frequency.
Either talk or listen
Requires only one frequency
and Push to Talk (PTT) switch
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12. Basic Transmitter Transmitter RF Heat Audio DC
Audio – 300 to 3,000 Hz DC – 12 to 14 VDC RF
Transmitter Black Box showing Inputs and Outputs
Audio is bandpass filtered inside transmitter to 300 to 3,000 Hz
DC power in is about twice RF power output; the difference is given off as heat.
Heat – just a few watts
Chapter 3 will look inside the VHF-FM transmitter
Chapter 7 will look inside the MF/HF SSB transmitter
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13. Decibels 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
The unit Bel or Decibel (one-tenth of a Bel) was named in honor off Alexander Graham Bell.
The scale is based on a logarithmic system as shown in the formula.
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14. Basic Receiver Receiver RF DC – 12 to 14 VDC Audio RF Heat DC
Audio – 300 to 3,000 Hz
Receiver Black Box showing Inputs and Outputs
Audio is 300 to 3,000 Hz (determined by transmitter) at 3 watts
DC power in is about twice the audio power output; the difference is given off as heat.
Heat – just a few watts
Chapter 3 will look inside the VHF-FM receiver
Chapter 7 will look inside the MF/HF SSB receiver
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15. Summary 1st emergency use of radio Half Duplex used by VHF-FM
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
The Titanic used Continuous Wave modulation to transmit Morse Code; AM was invented in 1906 but not used at sea.
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