Radio Theory

Question 1

Electromagnetic Spectrum

Answer 1

● As far as the Electromagnetic Spectrum goes, radio waves have low energy, long wavelengths, and low frequencies.

Question 2

Characteristics of Radio Waves

Answer 2

● The section of the Electromagnetic Spectrum known as Radio Waves is subdivided by their wavelengths and frequencies into further sub-classifications:
➢ Low Frequency (LF) / Medium Frequency (MF).
➢ High Frequency (HF).
➢ Very High Frequency (VHF).
➢ Ultra High Frequency (UHF)

Question 3

LF / MF Frequency Bands

Answer 3

● Frequencies
➢ 190 to 415 and 510 to 535 KHz are used by NDBs
➢ 550 to 1 750 KHz are used by AM radio.

● Low Frequency radio waves operate from 30 to 3 000 KHz.
● These frequencies have the largest (longest) wavelengths.
➢ Remember that the lower the frequency the larger the wavelength.
● These would include things like non-directional beacons, commercial radio stations, and marker beacons

Question 4

High Frequency (HF)

Answer 4

● The High Frequency range operates from 3 000 to 30 000 KHz.
➢ Ham radio operators call these frequencies “short wave”.
● High frequency radio is used mainly for long range air and ground communications.
➢ Oceanic crossings and operations in the high North.
➢ Range is dependent upon conditions in the ionosphere.
➢ It is good to remember “Sun up Frequency up, Sun down Frequency down”.
● 5 680 KHz is used frequently in northern Canada where VHF communications cannot be established.
● HF is also utilized on Transatlantic flight

Question 5

Very High Frequency (VHF)

Answer 5

● These frequencies are used extensively in aviation for navigational aids and communications.
● Operate from 30 to 300 MHz

Question 6

VHF Bands

Answer 6

➢ 112.00 to 117.95 Mhz VOR (Canada).
➢ 118.00 to 137.00 MHz for Aviation Voice Communications (bigger data for bigger numbers)

Question 7

Ultra High Frequency (UHF)

Answer 7

● Operate from 300 to 3 000 MHz.
● Mostly used by military and government, however, DME is also
found in this range

Question 8

Ground Waves

Answer 8

● These are radio waves that follow along the surface of the earth.
● They are able to diffract or “bend” around obstacles and this causes them to follow the curvature of the earth.
● Surface attenuation is one way in which these waves follow the curvature of the earth.
➢ It can be thought of as part of the wave coming into contact with the surface of the earth and getting “slowed down”.
➢ This causes a downward tilt in the wave
- since it’s lf/mf, waves are longer and hit the earth less, so attenuate less

Question 9

Sky Waves

Answer 9

● These are radio waves that are sent up towards space and then reflected back to the earth from the ionosphere.
➢ This reflection allows the sky waves to travel a very long distance;
➢ Often far beyond where the ground waves stop.
● The area between where the ground waves end and the sky wave touches back down at the earth’s surface is called the skip zone.
➢ Within the skip zone the signal will be erratic or non-existent

● Sky waves will travel further at night than during the day.
● They can also be affected by solar activity and other electromagnetic disturbances.
● LF, MF, and HF utilize both ground and sky waves for propagation.
● VHF and UHF typically penetrate the ionosphere and speed out into space, due to this fact these frequencies are also known as line-of-sigh

Question 10

Line-of-Sight

Answer 10

● Very High Frequency waves do not bounce or bend along the ground like the Low, Medium and High Frequency waves.
➢ For this reason they are line-of-sight only.
● VHF is relatively free of atmospheric and precipitation static

Question 11

HF Single Sideband (SSB)

Answer 11

● In a normal AM signal we have three components.
➢ The carrier
➢ Two sidebands
○ They are called the Upper Sideband and the Lower Sideband.
● Single Sideband (SSB) is a type of HF radio transmission in which only one of the sidebands of the signal is allowed to be transmitted.
➢ The other sideband and the carrier are suppressed.
● Once the signal gets to the receiver the carrier can then be re-inserted.

● Why do we do this?
➢ A fully amplitude modulated (AM) signal has two thirds of its power sent out in the carrier and only one third in each of the sidebands.
➢ By eliminating the carrier and emitting only one sideband, the transmitter’s available power is used to greater advantage.
➢ These lower power requirements allow SSB messages to be transmitted over several thousand miles.
➢ SSB also compresses speech into a much narrower bandwidth.
(3 KHz as opposed to 9 KHz for a normal signal)
➢ Because of this SSB conserves spectrum space