Ham Radio: Impedance-1: Why

[last updated: 2021-01-06]
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go to: Impedance-2: What
go to: Impedance-3: Reactance
go to: Impedance-3a: Reactance Physics
go to: Impedance-4: Coordinate Systems
go to: Impedance-5: Imaginary Numbers
go to: Impedance-6: Inverse quantities

go to: Impedance-?: Extra class Exam Questions

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Why do hams care about impedance?
• Hams use radio waves to communicate to other hams thousands of miles away.
• To do that, they need three things:
  • First they need a radio, that is, a transmitter that creates radio waves.
  • Second they need an antenna, to send the radio waves out into the air.
  • And third they need a "transmission line" to connect the radio to the antenna.
• There are a lot of options for each of these things - lots of different transmitters, lots of different antennas, and lots of different transmission lines.
• But all of them have a property called impedance.
  For example you might have heard that a typical coax cable (transmission line) might have 50 ohms of impedance,
  or that a perfectly balanced dipole antenna has an impedance of 72 ohms.

• Here's the clincher:
  • If you connect two things together
    that have different impedances, at the least you'll lose power - wasted as heat in your wires,
    and at the worst you can damage your transmitter.

  • This is why you care about impedance:
    so that whenever you connect two things together,
    you know they have the same impedance, so the power transfer between them will be efficient
    without a lot of wasted heat.
    You'll maximize your propagation (the distance away that your signal can be heard)
    while using a minimum amount of transmitter power.

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So that's why we care, but what exactly IS impedance???
Impedance-2: What

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