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Basic Radio Set-Ups and Operations

Basic Radio Set-Ups and Operations. Compare Book Chapter 2 sections 2.4 and 2.5. A Basic Radio Set Up. A source of power Battery Power supply Cigarette Lighter A transceiver (the radio) A connecting line

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Basic Radio Set-Ups and Operations

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  1. Basic Radio Set-Ups and Operations Compare Book Chapter 2 sections 2.4 and 2.5

  2. A Basic Radio Set Up • A source of power • Battery • Power supply • Cigarette Lighter • A transceiver (the radio) • A connecting line • Coaxial cable most commonly used because its easy to use and does not have special installation requirements (T9C12) • Coaxial cable commonly has an “impedance” of 50 ohms (T9C11) • TV coax cable is 75 ohms – they are not interchangable • An Antenna

  3. The Antenna • Right Antenna is cheapest most effective way to get good performance • Antennas like string on a violin – length is related to what frequency they put out well • A dipole antenna works best when it is ½ the length of the radio wave it is sending • The Antenna becomes shorter as the frequency of the radio wave increases (ie as the radio wave gets shorter) (T9A05)

  4. Getting It Wrong • Feed lines need to be efficient • Small feed line going long distance eats up your power before it is ever sent out • If Antenna is a bad match the power will bounce back down the feed line (of course you loose power bouncing things back and forth down the line) • Power Lost in the Feed Line is Converted to Heat (T9C05)

  5. Measuring a Bouncing Wave In a Feed Line • If power is bouncing back and forth in a feed line it forms a wave that doesn’t move called a standing wave • A measure of the size of the wave is called a Standing Wave Ratio (SWR) • The Standing Wave Ratio is a measure of how well the load (feed line and antenna) is matched to the transmitter (T9C01) • If it is perfectly matched the SWR is 1 to 1 (T9C02) • Low SWRs are good – big SWRs are bad • It is important to have a good SWR because it allows an efficient transfer of power(T9C08) • Protection Circuits in solid state transmitters will start reducing transmitter power is SWR goes above 2 to 1 (T9C04)

  6. How Do You Measure SWR • With an SWR Meter! • SWR meters work by measuring power going forward down the line and then measuring power coming back down the line • Other than a SWR Meter you can measure how well your antenna and feeline match using a directional watt meter (T9C06) • Many SWR meters are cross needle type and in fact work directly off a directional watt meter

  7. Where do I get an SWR Meter? • You can order one from various radio suppliers • But you may have better things to do than spend $40 to $250 bucks on one • Since need them mostly when you first set up work together with people in ward (Rick Fletcher and I both have one) • SWR meters also good for trouble shooting • If you get erratic changes in SWR reading most likely cause is a loose connection in your antenna or feed line (T9C03)

  8. How Radios Code Signals into Radio Waves • Length of a radio wave is it’s wavelength • Height of a radio wave is it’s amplitude • I could code information by adjusting the height of a radio wave • Called Amplitude Modulation (AM) • Any guesses on how an AM radio works? • An AM radio sends out three close radio frequencies • The number of different close frequencies needed to code a message is called the bandwidth • Not using too much bandwidth leaves more space for other messages

  9. The AM Signal • Sends out a steady signal called the carrier • This is the exact frequency you tune to • Consider a voice transmission • Voice Transmissions are called “phone transmissions” in radio terms (T6A01) • Radio takes voice frequency and adds it to the carrier frequency sends it at just a little higher frequency than the carrier tone • Radio also takes voice frequency and subtracts it from the carrier frequency sends it just at just a little lower frequency than the carrier tone • Gives the Radio two copies of the same information

  10. Ideas for Conserving Band Width • What if we only send one of the three signals? • Best conservation of bandwidth is to just turn the carrier tone off and on. • Makes beeps – Morse Code – CW • The Emission Type with the narrowest bandwidth is CW (T6A06) • We Could Also Send Just One of the “Side Bands” – Called Single Side Band • When going for Longer Distance or using a weak signal VHF and UHF will commonly use SSB (Single Side Band) (T6A04) • VHF and UHF most commonly use the Upper Side Band (T6A07)

  11. Another Way of Coding A Signal • Can stretch out or shorten the wave length being sent • This is called Frequency Modulation (FM) • Any guesses on how an FM radio works? • Frequency modulation uses the most bandwidth • FM uses all the frequencies over a range of from 5 to 15 kilohertz (kilo hertz means 1000 hertz) (T6A10) • SSB by contrast uses only 2 to 3 kilohertz(T6A09) • The primary advantage of SSB over FM for voice transmission is that it uses much less bandwidth (T6A08) • FM is still the most commonly used form of modulation on most VHF and UHF repeaters (T6A04) • All the repeaters around here use it • Almost all radios you will commonly buy are FM

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