This simple little circuit can be used for AM, FM, and Shortwave. On the shortwave band this active antenna is comparable to a 20 to 30 foot wire antenna.
R1 = 1M
C1 = 470pF
C2 = 470pF
L1 = 20uH to 470uH
Q1 = MPF102, 2N4416, or NTE451
L1 can be selected for the application. A 470uH coil works on the AM band, for shortwave try a 20uH coil. This unit can be powered by a 9 volt alkaline battery. If a power supply is used, bypass the power supply with a 0.04uF capacitor to prevent noise pickup. The antenna used on this circuit is a standard 18 to 48-inch telescoping whip .The heart of this circuit is Q1, a JFET-N-Channel, UHF/VHF amplifier in a TO-92 case. Although many different types of FET’s may be used–such as the MPF102, or the 2N4416–bear in mind that the overall high-frequency response is set by the characteristics of the FET amplifier. The direct replacement for the MPF102 is the NTE451. Output is taken from jack J1 and run to the antenna-input of your receiver.
This can be easily built on a small multi-use pcb and I have added a switch to switch in and out the inductor. It can make a difference to signal levels depending on the antenna being used. Use a banana or so-239 jack on the output for J1.