Page 256 - Build Your Own Transistor Radios a Hobbyists Guide to High-Performance and Low-Powered Radio Circuits
P. 256
FIGURE 15-4А Multiplied-unit-pulse-train signal with а "drawn" outline
to denote the envelope of the resulting sampled signal.
As stated in Chapter 14 for а single-transistor mixer, we found that increasing the
sinusoidal input into the transistor's base-emitter junction causes the collector
current to output а narrower and narrower pulse. And we found that the narrower
the pulse, the тоге harmonics were generated. For example, for а transistor mixer,
increasing the oscillator's signal level to 0.52 volt peak into the base-emitter
junction causes the second and third harmonic signal amplitudes to almost match
the amplitude of the fundamental. See ТаЫе 14-4, where the conversion
transconductances of the second and third harmonics аге within 20 percent of the
fundamental oscillator frequency for а O.52-volt peak sinusoidal waveform.
Thus we сап surmise that а pulse train of narrow pulses has frequency components
consisting of harmonics that аге almost the same amplitude as the fuлdаmепtаl.
Also, а positive-going pulse train also must have ап average ОС term.
А periodic pulse-train signal, where опе of the pulses is ап even function that is
centered at the origin at t = О, сап Ье written as
