This simple little circuit can be used for AM, FM, and Shortwave(SW). On the shortwave band this active antenna is comparable to a 20 to 30foot wire antenna. It is further more designed to be used on receivers that use untuned wire antennas, such as inexpensive units and car radios.
L1 can be selected for the application. A 470μH coil works on lower frequencies and lie in AM, for shortwave try a 20μH coil. This unit can be powered by a 9 volt alkaline battery. If a power supply is used, bypass the power supply with a 0.04μF capacitor to prevent noise pickup. The antenna used on this circuit is a standard 18-inch telescoping type, but a thick piece of copper, bus-bar, or piano wire will also work fine.
The heart of this circuit is Q1, a JFET-N-Channel, UHF/VHF amplifier in a TO-92 case.It can be replaced with an NTE451.Output is taken from jack J1 and run to the input on the receiver.