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 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

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)

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)

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)

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

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)

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

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

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)

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