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

>>

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

>>

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

>>

MComm Ch1 - 7

Comm System ElementsComm System Elements

Transmitter

Source

Modulator

Destination

Demodulator

ReceiverCommunications

Channel

>>

MComm Ch1 - 8

Simplex Vs. DuplexSimplex Vs. Duplex

• Simplex communications

• (Full) Duplex communications

• Half-Duplex communications

>>

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)

>>

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

>>

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

>>

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

>>