TBARC Extra
Class
Radio Signals
and
Measurements
DAZ 4/18/09
Sine Wave
Measurement Domains
• Time Domain
– Time on horizontal axis
– Amplitude on Vertical axis
– Common oscilloscope display
• Frequency Domain
– Frequency on horizontal axis
– Amplitude on vertical axis
– Spectrum analyzer display
Other Common Waveforms
• Sawtooth Wave
– Fast rise, slow fall or vice versa
– All harmonics, decreasing amplitude
• Square Wave
– Abrupt change between two voltages
– Odd harmonics only, decreasing amplitude
Radio Related Waveforms
• Speech
– Irregular Waveform
• Pulse waveforms
– Narrow bursts of energy
– Periods of no signal
– CW is an example
Definitions
• Peak to peak
– Voltage from maximum positive to maximum
negative
– Significant for evaluating class A amplifiers
• Peak
– Maximum positive or maximum negative
voltage
– Equal to ½ Peak to peak
– Equal to 1.414 times RMS voltage
More Definitions
• RMS (Root mean square)
– Value of DC voltage that will cause the same
heating in a resistor as the ac voltage
– Equal to 0.707 times the peak of a sine wave
– Effective voltage of an AC wave
• Average
– Voltage measured by a D’arsonval voltmeter
– Equal to 0.637 times the peak of a sine wave
Calculation Example 3
• What is the peak value of a sine wave with
an RMS value of 120 volts?
• VP = 120 x 1.414 = 170 volts
Calculation Example 4
• What is the peak to peak value of a sine
wave with an RMS value of 65 volts?
• VP = 65 x 1.414 = 91.9 volts
• VP-P = 2 x 91.9 = 184 volts
Calculation Example 5
• What is the peak value of a sine wave of
34 VRMS
• VP = 34 x 1.414 = 48 v
Calculation Example 6
• What is the peak to peak value of a sine
wave with an RMS value of 120 v?
• VP = 120 x 1.414 = 170 v.
• VP-P= 170 x 2 = 340 v
Calculation Example 7
• What is the RMS value of a sine wave
whose peak to peak value is 340 v?
• VP = ½ VP-P = ½ x 340 = 170 v
• VRMS = 0.707 x 170 = 120 v
RF Signal Power
• Unmodulated (CW, FM, PSK31)
– Power = VRMS2/R
• Peak Envelope Power (SSB)
– PEP = (PEVx 0.707)2/R
Calculation Example 9
• VRMS = VP x 0.707 = 35 x0.707 = 24.7V
• PAVG = 24.7/50 = 12.2 Watts
• What is the average power in a 50Ω load
during one complete RF cycle if the peak
voltage is 35 volts?
Calculation Example 11
• What is the PEP output power of a
transmitter that has a PEV of 30 volts
across a resistive load of 50Ω?
• PEP = (30 x 0.707)2/ 50 = 9 Watts
Electromagnetic Fields
• Radio waves are similar to light waves
• Composed of electric fields and magnetic
fields
• E fields and M fields are perpendicular to
each other
• Waves travel at the speed of light
– ~ 300 million meters per second
Field Polarity
• Polarity is defined as the orientation of the
electric field compared with the surface of
the earth
• Circular polarity is defined as rotating
polarity, may be right hand or left hand