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 107Harl@sc.rr.com Rear Commander for Electro-Mechanical Systems is R/C Gene Danko, SN Left is picture of Nikola Tesla, inventor of radio

Overview History Basic Communications System Simplex vs Duplex Basic Transmitter Decibels Basic Receiver Summary Major sections in this chapter >>

History 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 1857-1894 Tesla 1856-1943 Marconi 1874-1937 Fessenden 1866-1932 Details in text first paragraph of History >>

First Emergency Use 14 April 1912 from R.M.S. Titanic 1891-1956 1887-1912 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 >>

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 >>

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 >>

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 >>

Simplex Vs. Duplex Simplex communications (Full) Duplex communications Half-Duplex communications Sub-Topics in this section >>

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. >>

(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 >>

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 >>

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 >>

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. >>

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 >>

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. >>