small active antenna

This small active antenna published in the German magazine Funkamateur, 1999, № 7 is designed for receivers operating in the range from 6 to 30 MHz, provides radio stations in several radio and amateur radio bands . Active antenna has an input impedance of 50 ohms and is a frame , the frame is set to the operating frequency of a variable capacitor (C1). Frame active antenna is connected to the amplifier using bipolar transistors and field . FETs provide high input impedance and low input capacitance . This allows you to completely connect the frame to the amplifier and get a high transmission factor devices , as well as a large block without switching bandwidth. The amplifier of an active antenna used high field and bipolar transistors with a cut frequency of about 5 GHz. If the transformer T1 is made correctly you can get the bandwidth of the amplifier 1 ... 100 MHz. Transfer coefficient with its input to the load 50 ohm - about 1. Inductor L1 circuit FET drain VT1 and VT3 need to increase the input impedance of the amplifier at the high operating frequency portion of an active antenna . Chain of diodes VD1-VD6 need for voltage stabilization ( 4volta ) on the bases of bipolar transistors . Application Zener is not justified , since they generate a high-frequency noise stabilization mode can negate all the advantages of the amplifier. Current consumption of less than 3 mA , so it can be powered by compact battery 9 V . Transformer T1 is made on the annular yoke size K13h7 , 9h6 , 4 mm of ferrite with an initial permeability of 800 . I contain three winding coil and the winding II and III - 20 turns. Wire - Litz wire . Frame active antenna is formed from copper tubing with a diameter of 16 mm and has a ring shape with a slit 1m diameter , which is placed in the variable capacitor C1. Conclusions from the stator is connected to the frame and the rotor or not connected to anything . This minimizes the impact of hands when setting the operating frequency of the antenna . Frame mounted vertically on the insulating base on which you installed the capacitor C1 and the other elements of the amplifier , the battery power to the switch . The upper part of the frame is supported by a vertical bar insulation . Along it to the amplifier goes wire removal from the frame (just from its center ) . Q-factor framework for the 6 MHz - about 1000 . This provides a high transmission ratio device as a whole , and good filtering interfering radio signals . If the interfering station is receiving a strong signal and operates at a frequency close to the resonant frequency of the active antenna amplifier nonlinear effects manifest . Since the frame has a spatial selection , then these problems can be eliminated partially optimal orientation of the frame.