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Homework 5 - AM Transmission
Problem 1.
For an amplitude modulated double sideband full carrier (DSBFC) modulator with a carrier
frequency of 100kHz and a maximum modulating signal of 5kHz, determine (a) the frequency
limits for the upper and lower sidebands, (b) the bandwidth, (c) the upper and lower side
frequencies produced when the modulating signal is a single frequency tone at 3kHz, and
(d) sketch the output frequency spectrum.
{ Solution }
Problem 2.
What is the maximum modulating signal frequency that can e used with an AM double sideband
full carrier system with a bandwidth of 20kHz.
{ Solution }
Problem 3.
If a modulated RF wave with an average voltage of 20 volts peak changes in amplitude plus or
minus 5 volts, calculate the minimum and maximum envelope amplitudes, the modulation
coefficient, and the percent modulation.
{ Solution }
Problem 4.
Sketch and label appropriately, the envelope for Problem 3.
{ Solution }
Problem 5.
Provided a 30 volt peak carrier amplitude, find the maximum upper and lower side frequency
amplitudes for an amplitude modulated double sideband full carrier envelope.
{ Solution }
Problem 6.
For a maximum positive envelope voltage of +12 volts and a minimum positive envelope
amplitude of +4 volts, determine the modulation coefficient and percent modulation.
{ Solution }
Problem 7.
Draw and label all necessary voltage levels for the RF envelope for Problem 6.
{ Solution }
Problem 8.
Form an AM DSBFC envelope with a 40V positive maximum voltage and a 10V positive minimum voltage,
determine (a) the unmodulated carrier amplitude, (b) the peak change in amplitude of the
modulated wave, and (c) coefficient of modulation and percent modulation.
{ Solution }
Problem 9.
For an un-modulated carrier amplitude of 16V and a modulation coefficient of m = 0.4,
determine the amplitudes of the modulated carrier and side frequencies.
{ Solution }
Problem 11.
For an AM envelope shown in Figure 1, determine (a) the peak amplitude of the upper and lower
side frequencies, (b) the peak amplitude of the carrier, (c)the peak change in the amplitude
of the envelope, (d) the modulation coefficient, and (e) the percent modulation.
{ Solution }
Problem 12.
One input to an amplitude modulated double sideband full carrier modulator is an 800kHz
carrier with an amplitude of 40V peak. The second input is a 25kHz modulating signal whose
amplitude is sufficient to produce a plus and minus 10V change in the amplitude of the
envelope. Calculate the following:
Problem 13.
For a modulation coefficient of m = 0.2 and an unmodulated carrier power of 1000 watts
calculate, (a) the total sideband power, (b) the upper and lower sideband power, (c) the
modulated carrier power, and (d) the total transmitted power.
{ Solution }
Problem 14.
Determine the maximum upper, lower, and total sideband power for an unmodulated carrier power of 2000 watts.
{ Solution }
Problem 15.
Determine the maximum total transmitted power for an AM system defined in Problem 14.
{ Solution }
Engineering key words: AM, amplitude modulation, Tx, transmission, frequency spectrum,
carrier frequency, bandwidth, sideband, tone, pulse, full carrier, radio frequency, RF,
voltage level, modulation coefficient, spectrum envelope, carrier signal, amplitude,
waveform, peak to peak, power.
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