Page 236 - Build Your Own Transistor Radios a Hobbyists Guide to High-Performance and Low-Powered Radio Circuits

transconductance of a bipolar transistor mixer. Modified Bessel functions are rather

involved, and they generally are taught in senior year or graduate school university
classes. I wiU take a simplified approach instead, just showing the results of the
conversion transconductance as a function of oscillator signal injection voltage.
Simple Transistor Mixer and Its Conversion

Transconductance

Let me say at this point that I have probably overloaded quite a few readers with
equations and trigonometric identities to explain how distortion in amplifiers is used
in mixers or modulators. So this next section will detour back to a tabulated
approach. After all, the math can be interesting but also can sidetrack the reader.

See Figure 14-7, a simple one-transistor mixer. Figure 14-7 is a simp,le transistor
mixer circuit whereby the oscillator signal is combined with the RF signal to provide
typically an IF signal. Table 14-1 lists the tabulated ratios of conversion
transconductance to small-signal transconductance as a function of the oscillator
signa; I's peak amplitude.