HF & VHF antenna amplifier without coils

 Author:   Posted on:   Updated on:  2018-12-27T18:05:18Z

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, like MPSH10 and 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).

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.

HF & VHF antenna amplifier without coils

Here is the schematic of the amplifier. All capacitors are ceramic disc type. L1 RF choke can be omitted if you want to power the amplifier from a separate cable. If you will use the RF coaxial cable to power the amplifier (when it is mounted near the antenna), the RF choke is required.

Schematic of antenna amplifier without coils

Schematic of antenna amplifier without coils

It can be built on a single sided PCB of approximatively 32 x 76 mm. The PCB should be enclosed in a metal case and the entire amplifier should be mounted near the antenna for best performance. If you use L1, it can be built by winding 15-25 turns of 0.2-0.5 mm diameter copper wire on a 3-4 mm diameter ferrite rod. Or you can use a 5-10 microHenry inductor.

This is the component outline on PCB. My prototype photo above looks a bit different because it is a previous version.

Antenna amplifier PCB outline

Antenna amplifier PCB outline

The amplifier needs 6...12 V from a regulated power supply (max. 50 mA current draw). The gain is about 20 dB (according to LTspice simulation with MPSH10 transistor model).

Gain of antenna amplifier

Gain of antenna amplifier

The above circuit is based on an article from Romanian electronics magazine Tehnium.

Resources

4 comments :

  1. Hello sir, i amd low on circuits. Can i use it as gsm repeater?

    ReplyDelete
  2. Is it used to amplify RF signals and retransmit it ?
    I have a low powered FM transmitter, so can use this amplifier to increase the power of it?

    ReplyDelete
    Replies
    1. No! This is a receiving amplifier. You use it to boost signals from antenna and improve reception.

      Delete

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