14-20dB gain simple active antenna circuit diagram

  
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A very simple active antenna can be designed using this electronic circuit diagram. This active antenna is based on transistors and other few common electronic components. Because in practice of frequency short-wave reception, the general rule is that if the used antenna is longer, the stronger the received signal will be we need in some cases
14-20dB gain simple active antenna circuit diagram - schematic

( when we can not built a big antenna, because of some factors ). Antennas that are much shorter than 1/4 wavelength present a very small and highly relative impedance that is dependent on the received frequency. It is difficult to match impedances over a decade of frequency coverage. For this RF circuit a gain of 20dB is typical from 1-18 MHz, decreasing to 14dB at 30MHz. For this active antenna circuit many different types of JFET`s may be used, such as the MPF102, NTE451, ECG451 or 2N4416 and 2N3904 or 2N2222 transistor works well for Q2, Q3, and Q4. Transistor Q4 transform Q3`s relatively moderate output impedance into a low impedance, thereby providing sufficient drive for a receiver`s 50-ohm antenna-input impedance.



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