Active Shortwave Antenna PCB

Posted on Feb 4, 2014

The circuit of active shortwave antenna presented here boosts weak shortwave signals so that these can be heard with enhanced clarity over a shortwave receiver. Further, the receiver doesn`t require any physical connection as its placement in the vicinity (within 6 to 7 cm) of the circuit antenna will suffice. The circuit works well over a wide ra

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nge of supply voltage from 3 volts to 12 volts. Low-noise transistor T1 (BF494 or BF495) is connected as shown in the figure. Resistor R1 gives the DC bias to T1. R1`s value may lie anywhere between l00 kilo-ohms and 22 kilo-ohms; it determines the quiescent base-emitter current for transistor T1. Resistor R2 limits the current flowing through transistor T1 and, in conjunction with capacitor C2, determines the operating point for its stable operation. The number of turns in inductor L1 would have to be reduced as operation area shifts towards the upper end of the high-frequency band. A 180 H RFC in series with positive supply rail, along with a bypass capacitor to the ground, is recommended for reducing signal loss in the power supply. The current consumption is well below 10 mA. The transistor works well at maximum supply and so reduction of resistor R1`s value below 22 kilo-ohm is not recommended, as otherwise the transistor may burn off. This circuit works satisfactorily for boosting signals in 13m-49m band. However, as the frequency increases, its performance deteriorates. The same happens when the frequency decreases below that of the shortwave range. For input use a long wire as the antenna, while the output antenna wire may be limited to about 30 cm.

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