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Lecture 2: AM TransmissionPowerPoint Presentation

Lecture 2: AM Transmission

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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

ELC 222

AM Fundamentals

- Lower-Side Frequency (fc – fi)
- Carrier Frequency (fc)
- Upper-Side Frequency (fc + fi)

ELC 222

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.

ELC 222

Example 2-2

- Determine the %m for the following conditions for an unmodulated carrier of 80V peak-to-peak (p-p).

ELC 222

Example 2-3

- Determine the maximum sideband power if the carrier output is 1 kW and calculate the total maximum transmitted power.

ELC 222

Example 2-4

- A 500-W carrier is to be modulated to a 90 percent level. Determine the total transmitted power.

ELC 222

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?

ELC 222

Example 2-6

- The antena current of an AM transmitter is 12A when unmodulated but increases to 13A when modulated. Calculate %m.

ELC 222

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?

ELC 222

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.

ELC 222

Mathematical Representation of Sine Wave

- v = Vp sin(t + )
- Where v = instantaneous value
- Vp = peak value
- = angular velocity = 2f
- = phase angle
- AM: Amplitude Modulation
- FM: Frequency Modulation
- PM: Phase Modulation

ELC 222

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