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

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

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

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

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

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

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

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

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

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

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