1. Lecture 2: AM Transmission
Prof. Park
ELC 222
Essex County College
Prof. Park
ELC 222

2. Modulation
Modulation is the process of impressing a low-frequency intelligence signal onto a higher-frequency carrier signal.
The low-frequency intelligence signal
Intelligence
Modulating Signal
Information Signal
Audio Signal
The high-frequency carrier signal
Radio-Frequency (RF) Signal
Three Characteristics of Signal
Amplitude
Frequency
Phase
Prof. Park
ELC 222

3. AM Fundamentals Lower-Side Frequency (fc – fi) Carrier Frequency (fc)
Upper-Side Frequency (fc + fi)
Prof. Park
ELC 222

4. Example 2-1
A1.4 MHz carrier is modulated by a music signal that has frequency components from 20 Hz to 10 kHz. Determine the range of frequencies generated for the upper and lower sidebands.
Prof. Park
ELC 222

5. Example 2-2
Determine the %m for the following conditions for an unmodulated carrier of 80V peak-to-peak (p-p).
Max. Vp-p
Min. Vp-p
(a)
100 60
(b)
125 35
(c)
160
(d)
180
(e)
135
Prof. Park
ELC 222

6. Example 2-3
Determine the maximum sideband power if the carrier output is 1 kW and calculate the total maximum transmitted power.
Prof. Park
ELC 222

7. Example 2-4
A 500-W carrier is to be modulated to a 90 percent level. Determine the total transmitted power.
Prof. Park
ELC 222

8. Example 2-5
An AM broadcast station operates at its maximum allowed total output of 50 kW and 95 percent modulation. How much of its transmitted power is intelligence?
Prof. Park
ELC 222

9. Example 2-6
The antena current of an AM transmitter is 12A when unmodulated but increases to 13A when modulated. Calculate %m.
Prof. Park
ELC 222

10. Example 2-7
An intelligence signal is amplified by a 70% efficient amplifier before being combined with a 10-kW carrier to generate the AM signal. If you want to operate at 100% modulation, what is the dc input power to the final intelligence amplifier?
Prof. Park
ELC 222

11. Example 2-8
A transmitter with a 10-kW carrier transmits 11.2 kW when modulated with a single sine wave. Calculate the modulation index. If the carrier is simultaneously modulated with another sine wave at 50% modulation, calculate the total transmitted power.
Prof. Park
ELC 222

12. Mathematical Representation of Sine Wave
v = Vp sin(t + )
Where v = instantaneous value
Vp = peak value
 = angular velocity = 2f
 = phase angle
AM: Amplitude Modulation
FM: Frequency Modulation
PM: Phase Modulation
Prof. Park
ELC 222