Radio Waves and Signals

Week 4

We imagine radio signals/waves travel as sine waves.

The ripple of these waves are started by the vibration of an electron

The signal is produced in thecircuits of the radio, once the vibration leaves the radio through the antenna it becomes a radio wave.

Radio waves are just one part of the electromagnetic spectrum

An electromagnetic wave consists of a vibrating electric field and a vibrating magnetic field.

It is the electromagnetic wave that carries the radio signal between the transmitting and receivingstations.

The EM wave oscillates in such a way to mimic the signal that generated the wave.

A cycle is one complete vibration.

This diagram actually shows 3 cycles.

Wavelength (l) is the distance the wave travels in 1 complete cycle

The number of vibrations per second is the frequency.

Frequency is measured in Hertz (Hz): 1 vibration/sec is 1 Hz

1 second

What is the frequency of each wave?

2 Hz

10 Hz

AM stations broadcast in kilohertz (kHz)1330 KVOL broadcasts at 1,330,000 Hz

FM stations broadcasts in megahertz (MHz)96.5 KPEL broadcasts at 96,500,000 Hz

Test Question Alert!

What type of wave carries radio signals between transmitting and receiving stations?

Electromagnetic

Test Question Alert!

What is the name for the distance a radio wave travels during 1 complete cycle?

Wavelength

Test Question Alert!What term describes the number of times per second that an alternating current reverses direction.

frequency

In what unit is frequency measured?

Hertz

A Hertz is ____ vibration(s) per _____ second(s) 1 1

Test Question Alert!

What are the two components of a radio wave? (or any other wave in the electromagnetic spectrum)

Electric and magnetic fields

All radio waves travel at the speed of light (c) through a particular type of medium.

The speed of light through space is 300,000,000 m/s

Since all radio waves travel at the speed of light no matter what their frequency happens to be the following is true:

When length increases then frequency decreases

or

when length decreasesthen frequency increases.

Radio waves can be referred to by wavelength or frequency because the two are related by the speed of light.

c

f l

A wave with a length of 2 m means it has a frequency of 150,000,000 Hz

because

300,000,000 / 150,000,000 = 2

This frequency typically would be referred to as 150 MHz

The formula for converting frequency to wavelength in meters is : Wavelength in meters = 300 divided by frequency in megahertz.

300

f in MHz

lin m

To convert frequency to wavelength in meters divide 300 by frequency in MHz.

96.5 KPEL broadcasts at 96.5 MHz so the length of the waves is 300/96.5. The waves are approximately 3 meters in length.

What property does wavelength refer to?

The distance a wave travels during 1 complete cycle.

How fast does a radio wave travel? (Two acceptable ways to answer)

Speed of light or

300,000,000 meters/second

Describe the relationship between wavelength and frequency.

inverse

wavelength frequency

or

wavelength frequency

What is the formula for converting frequency into wave length (in meters)?

300 / Mhz

Approximate wavelengths are often used to identify the different frequency bands.

All types of radio frequency signals are referred to by the abbreviation RF, but for convenience the entire range is spilt into sub-ranges.

3000 MHZ

Communications at VHF and UHF are generally “line of sight” communications.

That is they travel directly from the transmitting station to the receiving station.

Normally used for local communication.

Direct (not via a repeater) UHF signals are rarely heard from stations outside your local coverage area because UHF signals are not reflected by the ionosphere.

The radio horizon is the distance at which radiosignals between two point are blocked by the curvature of the Earth.

The radio horizon is somewhat farther than the visual horizon because the earth seems less curved to radio waves than light waves.

UHF signals are often more effective from inside buildings than VHF signals because the shorter wavelength allows them to more easily penetrate the structure of buildings.

When using a hand-held transceiver inside a building you might want to choose to operate in a UHF band.

Knife-edge propagation is the term used to describe when signals are partially refracted around solid objects exhibiting sharp edges.

You might be able to use this phenomenon to get your signal around a building in an urban setting.

3 – 30 MHz

30 – 300 MHZ

300 – 3000 MHz

What is the name assigned to each of these frequency ranges?

Why are UHF frequencies usuallylimited to local communications?

UHF signals are not reflected by the ionosphere.

What do we call the distance at which radio signals are blocked by the curvature of the Earth?

Radio Horizon

Why is the radio horizon somewhat farther that the visual line of sight distance between two stations?

The earth seems less curved to radio waves than to light waves.

Why should you choose to use frequencies in the UHF band when using a hand-held receiver inside a building?

The shorter waves length allows them to more easily penetrate the structure of the building.

What do we call the phenomenon in which signals are partially refracted (bent) around solid objects with sharp edges?

Knife-edge propagation