The post explains a simple circuit which will boost the weak FM signals into stronger signals and will allow an FM radio to work more efficiently even in remote areas where the FM signals are unable to reach adequately.
Main Features
There are simple solutions for boosting the level of FM signals, such as the aerial amplifier. This amplifier has negligible noise at 1.6 dB and a gain of 22 dB.
Since the gain is more than three times higher than the noise level, the amplifier is able to keep the degradation of the signal to noise ratio at minimum proportions.
The amplifier’s BFT66 transistor (T1) has a common emitter configuration.
To balance the base bias, a current source (T2) is provided to stabilize the operation.
Please remember that the transistor should have low noise to keep the FM signals significantly traceable.
How to Wind the Inductors
The value of L1 is usually around 6 µH. However, we may choose to use any r.f. choke of 5.6 µH or 6.8 µH. A copper coil, L2, which has five to six turns of 0.25 mm is also used.
This coil is wound over a 5 mm former which is removed once the coil makes a solid circular pattern of 5 mm diameter. This wounded coil is then elongated or stretched to 10 mm for use.
To keep inductance and capacitance at the lowest levels, all components and leads should be made as short as possible.
The final circuit has to be mounted in a metal box within the minimum separating distance from the aerial.
An IC Voltage regulator can also be used to make the amplifier more reliable and compact. If there is no IC regulator, one can use a simpler circuit of a 680 Ω resistor in between C5 and C6.
It is also necessary to fit a 12V / 400 mW zener Diode and a 10 Ω / 16 V electrolytic capacitor in a parallel circuit with C5.
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