Very low noise transistor amplifiers in the u.h.f. band using the parametric conversion mode
Ulrich L. Rohde · Journal of the British Institution of Radio Engineers · 1962
The need for amplifiers with low noise and high gain in the ultra high frequency band led to the use of semiconductors in parametric amplifiers. Because such amplifiers are reciprocal devices, they must be used with isolators. This paper describes a new method of using available high-frequency transistors to achieve high conversion gain with extremely low noise figures in a small and simple non-reciprocal u.h.f. amplifier which avoids the expense of “varactor” diodes and isolators.