This is a simple active antenna circuit, for the radio receiver SW/MW/FM band. It is a circuit to try to work on many brands of radios. This circuit has a only 18-inch antenna, when used with short wave The radio receiver will be able to receive signals from stations around the world more clearly.
In experiments using this unit with a short wave radio listening is comparable as well. The antenna for shortwave radio with a length of 20-30 feet. When used with a The radio receiver frequency broadcast mw general, from the reception of some stations is poor. Will become a strong and clear signal better. And when using the FM tuner will make for a better signal than the antenna attached to the receiver.
This circuit is simple because it is untuned, and output high impedance able to work well with cheap radio. Which is designed for use with an antenna that is not tuned attached a that radio in the car. The active antenna, this will lead to a radio receivers amateur Which has low impedance input that does not work well.
-Important to select the L1, which is the Shock Coil (RFC) to the appropriate the band to use.
The prototyping machines coil L1 using the 470uH because want to the amplify the so signal at lower frequencies.
For those who want to apply to short-wave the band are may be to less L1 value as 20 uH.
-This circuit can be packed into a plastic box. If a metal box would be better for reduce noise that may occur better. To make a circuit can work well in the circuit wiring and connect the antenna cable into the jack and the output should be as short as possible.
-The coaxial cable 50ohm or 75 ohm is connected to the radio receivers should be the shortest. Do not lose the signal, too. The cable is used should be the low capacity in the car and the radio should not be used without a shield cover.
-This circuit used power supply between 6VDC to 15VDC.
In the case of some problems such as:
– Its strident On hearing of the stations may be possible that it oscillate with the active antenna and radio receivers. how to editor you reduced L1 to less down.
– If there are problems the battery voltage is less than normal, they should change the Q1 a new.
– Quiescent current is normally of Q1 (MPF 102) about 5mA, but may be increased to up to 20mA, which makes the demand on battery power.
– To use an external power supply circuit, a capacitor 0.047uF is connected across the power supply filter the based on circuit. Should be placed close to the Q1.
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