40 MHz Wideband RF Amplifier

Figure 1 

The objective of the circuit is to design an amplifier that will be used under radio frequency range with a wideband frequency of 40 MHz.

• Radio Frequency (RF) – a rate of oscillation or frequency that operates within the range of 3 Hz to 300 GHz
• Wideband – a transmission or communication channel or medium which consists of a wider bandwidth than one voice channel with a carrier wave of a certain modulated frequency and is capable of transmitting more information than narrowband but less than broadband
• AF125 – a high frequency germanium PNP transistor operating at 75 MHz, with voltage of 20 V at 10 mA current, enclosed in a TO-72 package, and used for RF & IF amplifier, preamplifier mixer, FM mixer, and oscillator up to 900 MHz

The input of the circuit comes from the BNC jack where the sensitivity of the receiver can be adjusted to increase accordingly. This can be achieved in the presence of interference between the circuit and the aerial source of the RF amplifier. The resonant circuit used in the amplifier circuit is made to be suitable for mid waves and for the low waves which oscillates up to 40 MHz.
The circuit is consuming a total of 7 mA of current while the gain is in the measurement of 20 dB. All these values are due to the presence of a 12 V up to 15 V DC supply. The input and the output of the circuit are designed to be compatible with coaxial cables with complex resistance of 75 Ohms. Short coaxial cables are being used for ham radio setups, home video equipment, and in measurement electronics while long coaxial cables are used for connecting television, radio networks or telephone companies. There are some problems that have been encountered in using coaxial cables such as ground loops, common current and radiation, induction, signal leakage, and transformer effect.

Figure 2 

The idea behind the construction of wideband RF amplifiers may be found in RF measuring equipment, communication receivers like GPS receivers, and other related devices. They are designed to operate in conjunction with its series of waveform generators that will provide a solution for wideband, high-voltage applications.

Source:users.otenet.gr/~athsam/RF_amp_wide_band.htm

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