Modulation 1-50

• Result of gain level being too high for signals entering the modulator: Distortion and splatter
• Amplitude modulation causes the amount of transmitter power to increase
• When a carrier is modulated 100%, the total power increases by 50% over that of the carrier alone
• When the amplitude of the modulating voltage is increased for AM, the antenna current will increase
• Modulation index will be increased by a factor of √2 when a second modulating tone with the same amplitude but a different frequency is added to the first at the input to the modulator
• Modulation methods used for a common-emitter configuration: Base modulation and collector modulation
• Unwanted sidebands in SSB equipment can be suppressed by phasing method and filter method
• Envelope detection is concerned with the process of rectification
• Diagonal clipping in envelope detection will result in distortion
• Product detection requires the process of heterodyning
• A sine wave that is coherent with the carrier has identical frequency and phase angle
• Frequency modulation and phase modulation are collectively referred to as angle modulation
• In FM, the change in carrier frequency is proportional to the amplitude of the modulating signal
• A louder sound generating the modulating waveform for FM will cause a greater frequency deviation
• Device whose capacitance is deliberately made to be a function of the applied voltage: Varactor diode
• Reactance modulator is one method of obtaining direct FM
• Device useful for direct FM and as one element in the phase-locked loop: VCO
• Frequency change process where phase deviation and frequency deviation are multiplied by some fixed constant: Multiplication
• Circuit that demodulates the frequency-modulated signal: Foster-Seeley discriminator
• Ratio detector is superior to the slope detector because it is less sensitive to noise spikes and interference causing AM
• One implementation of a pulse-averaging discriminator is a triggered multivibrator
• Two different signals can be coherent if they have the same frequency
• Quadrature detector requires that the inputs are coherent
• In a phase-locked loop, the VCO stands for voltage-controlled oscillator
• Advantages of a properly designed FM system: Relative immunity to atmospheric noise (lightning)
• Output of a balanced modulator: LSB and USB
• If the modulation index of an AM wave is changed from 0 to 1, the transmitted power is increased by 50%
• If the unmodulated level peak carrier amplitude is doubled in an AM signal, the perfect modulation is 100
• Balanced modulator circuit when inserted in the equivalent suppresses the carrier
• Carrier of a 100% modulated AM wave is suppressed, and the percentage power saving is 66.66%
• If the modulation index of an AM wave is doubled, the antenna current is also doubled, the AM system being used is J3E
• 100% modulation in AM means a corresponding increase in total power by 50%
• Single-tone amplitude modulated wave has 3 components
• Carrier signal has constant peak amplitude
• Modulating system is frequency modulation if the modulating frequency is doubled, the modulation index is halved, and the modulating voltage remains constant
• Modulation index of an FM signal if its modulating frequency is doubled is one-half the original index
• AM transmitter rated 1000 W at 100% modulation requires 666.6 W for the carrier
• Standard way of designating AM: A3E
• Circuit used to detect frequency-modulated signals: Discriminator
• Information signal sent directly without modulating any carrier: Baseband