barcode generator excel mac Figure 216 A single-sideband in Software

Printing UPC Code in Software Figure 216 A single-sideband

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The SSB transmitter (Fig 218) creates a single-sideband signal by inserting both the oscillator (OSC) generated carrier and a modulating audio signal from the AUDIO AMP into the balanced modulator The balanced modulator nonlinearly combines, or mixes, the carrier and baseband inputs, producing both lower and upper sidebands The modulator will also severely attenuate the carrier from the OSC stage by phase cancellation or common-mode rejection methods The ensuing double-sideband (DSB) suppressed carrier signal is then injected into the next stage, which is an upper sideband/lower sideband (USB/LSB) filter These filter stages of the SSB transmitter consist of very selective bandpass filters that have a center frequency to pass either the upper or lower sidebands There are nonfilter phase-cancellation methods that can be utilized to reject the undesired sideband by twin balanced modulators and phase-shifter circuits Either way, the SSB signal is then upconverted, amplified, and sent out through the antenna However, since the modulated signal will contain a nonconstant amplitude modulation envelope that can easily become distorted, linear amplifiers must be utilized throughout an SSB system s signal path The RF signal is then picked up at the SSB receiver s antenna, filtered, amplified, and downconverted (Fig 219) The signal is inserted into a type of nonlinear mixer called a product detector, along with the carrier oscillator [or beat frequency oscillator (BFO)] frequency to supply the missing carrier The

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output is the baseband signal, which is amplified and sent on to headphones or speakers Depending on the number of modulating tones and their amplitude, different time-domain outputs can be viewed on an oscilloscope If a single baseband tone is injected into an SSB modulator, a steady RF signal in both amplitude and frequency will be created, as in Fig 220 This is simply a CW signal However, a two-tone baseband signal will generate the consummate SSB modulation envelope display of Fig 221, with the amplitude of the modulation envelope dependent on the baseband modulation level The two-tone RF signal will start to flat-top (Fig 222) if overmodulation occurs, causing extreme distortion and spurious outputs

The measurement of output power in SSB is the same as in AM, the peak envelope power (PEP) being the measurement of the average peak power of the transmitted signal with 100 percent modulation PEP can be calculated by V 2RMS/R, or VRMS IRMS, or I 2RMS R, where V and I are those of the maximum modulated peak

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With the advent of digital modulation techniques, far higher data rates are possible within constrained bandwidths, and at higher reliability and noise immunity levels, than the older analog modulation methods of FM, AM, frequency shift keying (FSK), on-off keying (OOK), pulse width modulation (PWM), pulse position modulation (PPM), pulse amplitude modulation (PAM), etc The newer digital modulation has much in common with some of the older discrete digital/analog modulation methods, such as OOK and FSK, in that it has discrete states at discrete times whether these states are amplitude, phase, or amplitude/phase and these states define the information being transmitted, while the number of states possible governs the amount of data that can be transmitted across the link However, digital modulation may be considered to be only the QAM, QPSK, and BPSK modulations (defined below), and their many variants