Instruction manual

SM100 • 4

INTRODUCTION

From the earliest days of radio until the present, news, sports, and “talk”

radio broadcasts have been transmitted using an (A)mplitude (M)odulated

waveform. This type of transmission ensured reliable broadcasts with a large

transmission range. In fact, large AM transmitters are used on the shortwave

radio bands to send signals around the world! Sounds almost to good to be

true? Well, there are a few disadvantages.

Lets take a look at an AM waveform. It consists of two parts, the “carrier”

frequency, which is the frequency that you tune on your radio dial, and the

“modulation,” or intelligence that is transmitted like your favorite talk show or

Buffalo Bills game.

The inherent problem with AM is that this

audio information is encoded in the

amplitude of the waveform, making it

susceptible to a variety of outside

interferences. Have you ever noticed the

crackle on your AM receiver during a

lightening storm? Or how about the car

radio when we pass beneath a high

tension power line? What you are actually

hearing is an electrostatic waveform that is overpowering the AM detector, or

decoder. The burst of electrostatic energy actually becomes part of the AM

waveform.

Also, even though AM signals can carry great distances, a transmitter with a

powerful carrier signal can overpower a more distant station operating on or

near the same frequency. In some cases, the transmitter power is turned

down at sunset to avoid such interference.

In addition to the electrostatic field generated by the transmitter, an

Low Frequency Audio Waveform

High Frequency Radio Carrier

Amplitude Modulated Signal

noise "spikes"

encoded in wavefor