How to make VHF antenna amplifier without coils?

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dondon pramis
Location: Philippines
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Joined: Sun Feb 12, 2017 8:28 am

How to make VHF antenna amplifier without coils?

Fri Nov 30, 2018 12:50 am

The following receiving amplifier can be used for any kind of signal in the HF and VHF bands from about 1 MHz to 400 MHz. It offers quite linear gain across this band width without using any LC tuned circuits. Therefore it can be used for shortwave, FM and VHF signals and even AM band can be received, because the gain at 500 kHz is not less than 18dB. The circuit does not use coils. However, a choke will be required if you will power the amplifier through the feed cable.
The circuit uses five RF transistors with a cut-off frequency of at least 600 MHz. The PCB is designed for the (S)S9018 transistors (EBC pinout), but you can use any kind of low power RF NPN transistors, even the old types like BF200 or BF214 (pay attention to pinout). S9018 transistors are cheap and widely available (you can find them in transistor packs).
VHF-Antenna-Amplifier-without-coil.png (50.73 KiB) Viewed 360 times
The amplifier's input is unbalanced and it can be connected to any kind of antenna (after the balun if it is necessary). Because Q5 is placed in a common base configuration, the input impedance is high, thus the amplifier can be used with whip antennas too (they usually have high impedance at low frequencies). The output is 75 ohms unbalanced. The overall gain of this amplifier is 20 dB.



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