RF Amplifiers

A linear amplifier is an electronic circuit whose output is proportional to its input, but capable of delivering more power into a load. The term usually refers to a type of radio-frequency (RF) power amplifier, some of which have output power measured in kilowatts, and are used in amateur radio. Other types of linear amplifier are used in audio and laboratory equipment. An RF linear amplifier can be based on either solid state or vacuum tube technology.

Most commercially manufactured one to two kilowatt linear amplifiers used in amateur radio still use vacuum tubes (valves) and can provide between 10 to 20 times RF power amplification. For example, a transmitter driving the input with 100 watts will be amplified to 2000 watts (2 kW) output to the antenna. Solid state linear amplifiers are more commonly in the 500 watt range and can be driven by as little as 25 watts. However, AM radio broadcast transmitters of up to 50 kW are now solid state.

Large vacuum valves are still used for international long, medium, and shortwave broadcast transmitters between 500 kW up to 2 MW. The basic applications of the RF power amplifier include driving to another high power source, driving a transmitting antenna, microwave heating, and exciting resonant cavity structures. Among these applications, driving transmitter antennas is most well known. The transmitter–receivers are used not only for voice and data communication but also for weather sensing (in the form of a RADAR).

Microwave or RF heating is an industrial application which is also benefiting our homes in the form of microwave ovens. Class-A operation is characterized by a constant DC collector (or drain) voltage and current. This class of operation is required for linear amplifiers with severe linearity requirements including: Drivers in SSB transmitters where a 2-tone 3rd-order intermodulation of at least -40 dB is required. Drivers in TV transmitters where the contribution to the gain compression must be very low, i.e. not more than a few tenths of a dB.

UHF TV Linear Amplifier (450-800MHz)

UHF TV Linear Amplifier (450-800MHz)

This structure is an amplifier RF, covering the range of UHF and intended for small TV transmitters, working in the channel UHF. The amplifier can enhance any video signal to the region UHF (450-800MHz). The circuit operates in class A and uses the known transistor BFQ68. The construction, though simple, we can say that is quite critical, due to the nature of the high frequencies. The construction is a double-sided printed circuit with conventional materials, although we used only two capacitors surface mount. We preferred not to use it anywhere a surface support, to enable easier the reader to make the construction. The strengthening of the transistor is 13dB, for an operating frequency of 800MHz, voltage emitter and collector Vce = 15n and current func tioning 240mA. If you give him a driving force 100mW, then the output will providing a power of about 2W. ..

CMOS inverters linear amplifier circuit

CMOS inverters linear amplifier circuit

CMOS inverters can be used as linear amplifiers where negative feedback is applied. Best linearity is achieved with feedback applied around three inverters which gives almost perfect linearity up to a dynamic output of 5 V peak to peak with a 10 V supply rail The gain is set by the ratio of Rl and R2 and the values are typical for a gain of 100. The high frequency response with the values given is almost flat to 20 kHz. The frequency response is determined by Cl and C2.. ..

1W Linear FM Booster

1W Linear FM Booster

That RF Amplifier is for boosting small fm transmitters and bugs. It use two Philips 2N4427 and its power is about 1Watt. At the output you can drive any linear with BGY133 or BLY87 and so on. Its power supply has to give 500mA current at 12 Volts. More voltage can boost the distance but the transistors will be burned much earlier than usual.! In any case do not exceed the 15Volts. ..

Wide band 10MHz 500MHz RF amplifier

Wide band 10MHz 500MHz RF amplifier

This paper describes an RF amplifier circuit which is suitable for the frequencies between 10MHz and 500MHz. These kind of amplifiers are called wide band amplifiers. Wide band amplifiers are used in communication receivers, RF measuring equipment and tons of other devices. The circuit described here uses a state of the art transistor to get maximum performance at high frequencies. It can be used as a low noise pre-amplifier due to his low noise characteristics. ..

HF 1-30MHz linear amplifier

HF 1-30MHz linear amplifier

This project was a particular surprise for me in that the BC547 (equiv 2N2222) can be used to build a 500mW linear amplifer covering the entire HF band with excelent spectral purity and no neutralising at all. Ugly-bug construction was used but I dare say that the good results are partly to do with the method of construction. The circuit is fairly straight-forward and does not even need any form of RF neutralising. Two pairs of BC547 transistors are used in a push-pull type of output stage, biassed by a single diode and resistor. The driver is also very conventional using T1 to transform the drive impedance to a very low value for the output pairs. ..

HF SSB CW AM RF Linear amplifier

HF SSB CW AM RF Linear amplifier

This is a rather unusual QRP Power Amplifier design, with a wide frequency response; within three dB's from 300KHz to 30MHz. Overall gain is in the region of 16dB and the final output power may be well over four watts. The wide bandwidth is a result of the construction of the RF transformers, T1 and T2. These are wound on 2-hole ferrite balun cores as commonly found in the old fashioned valve TV sets (e.g. Phillips 4322-020-31520). Twist 2 lengths of 22 SWG enamelled wire together and wind as shown. Connect the end of the "A" winding to the start of the "B" winding. Use this junction as the centre-tap of the transformer. ..

10 Watt CB Linear amplifier

10 Watt CB Linear amplifier

It is quite easy to get a watt or more with very simple equipment, but to get more than 5 watts becomes a little more difficult. This article describes a 10 watt linear amplifier that is capable of delivering over 15 watts into 50 ohms and uses cheap plastic transistors that are used in CB equipment. If you have difficulty in finding 2SC2078 then lift the lid of your CB set to find a suitable alternative. The bias generator transistor, TR4, is marked TIP31 in the circuit diagram, but here you can use just about anything that will fit. You could even use another 2SC2078, if you had money to burn, but more practical components would be TIP41, TIP3055, MJE3055. All that matters is that it will pass up to 1 Ampere and have the correct base details in a TO220 case...

2 Watt VHF linear amplifier

2 Watt VHF linear amplifier

Once again my collection of projects creation has been interrupted by another necessity. Patrick and other people have asked me for a circuit of a VHF power amplifier. These circuits are my "standard" building blocks that can be used to amplify RF power signals, from 50MHz to 170MHz, just a few component changes are required. The circuit diagrams shown are "normalised" for 100MHz and will tune about 80MHz through to 120MHz. Simply scale the components up or down if you want to go down or up in frequency bands. The circuits as shown will give a gain of about 14dB with an output power of about 2 Watts (input = 100mW). With an output power of 20 watts the gain falls off to just 12dB at 100MHz or just 10dB at 170MHz...

450 watts / 3.5-30 MHz Linear amplifier

450 watts / 3.5-30 MHz Linear amplifier

This is the circuit of a 500 watt linear amplifier, based upon a design by Frits Geerligs, PA0FRI, who has his own homepage at http://home.planet.nl/~fhvgeerligs. The circuit uses four PL519 TV line output valves in a very simple circuit that will deliver over 450 watts at 3.5 MHz (350 watts at 30 MHz). PL519 (40KG6A) is a more robust replacement for the earlier PL509 (40KG6) tube. Both valves will work well in this circuit. The input drive power is about 50 - 100 watts so it is compatible with most amateur radio HF transmitters. Not shown in the circuit is the cooling fan that is required to force air around the valves to cool them. In operation the 1K0 pot is adjusted to set the total valve anode current to around 50mA to 70 mA. ..

VHF preamplifier with BFY91

VHF preamplifier with BFY91

When the start switch is pushed, the output of the charger goes to 14.5 V. As the batttery approaches full charge, the charging current decreases and the output voltage is reduced form 14.5V to about 12.5V, terminating the charging process. Transistor Q1 then lights the led as a visual indication of a full charge. The actual preamplifier in this circuit is a practical wideband amplfier that gives about 15 - 20dB of gain from 1.8 MHz through to well over 200 MHz. You will no-doubt replace this circuit for your own favorite amplifier for the band you are interested in. The 2.2mH chokes should have an absolute minimum reactance of 5000 ohms at the lowest frequency to be used. For 145 MHz these may simply consist of a few turns of wire. I personally used a 10-turn 4mm Dia. coil in series with a 2.2mH torroidal inductor...

30MHz 500 watt linear tube amplifier

30MHz 500 watt linear tube amplifier

This is the circuit of a 500 watt linear amplifier, based upon a design by Frits Geerligs, PA0FRI. The circuit uses four PL519 TV line output valves in a very simple circuit that will deliver over 450 watts at 3.5 MHz (350 watts at 30 MHz). PL519 (40KG6A) is a more robust replacement for the earlier PL509 (40KG6) tube. Both valves will work well in this circuit. The input drive power is about 50 - 100 watts so it is compatible with most amateur radio HF transmitters. Not shown in the circuit is the cooling fan that is required to force air around the valves to cool them. In operation the 1K0 pot is adjusted to set the total valve anode current to around 50mA to 70 mA. ..

IF Amplifier using NE592

IF Amplifier using NE592

In this circuit, an NE592 acts as an IF amplifier. DC coupling between mixer and amplifier is practical beacuse different + 6 V and + 12 V supply voltages are used. The voltage at the differential input is about 4.5 V. A narrow bandpass filter for the intermediate frequency is achieved using only one crystal as the reactive element. Maximum IF gain is at the crystal series resonance, where the crystal impedance is very low. The capacitor across the amplifier input is intended to suppress mixing products that have a higher frequency than the IF. You cannot do without this cap because parasitic stray capacitance in parallel with the crystal causes unwanted amplification at frequencies higher than the crystal resonance, and thus degrades the IF selectivity...

RF Recieving Amplifier for 40MHZ

RF Recieving Amplifier for 40MHZ

The sensitivity of receiver it is possible to increase itself considerably, if is interfered, between this and his aerial, a amplifier RF. The amplifier of circuit, does not use in resonant circuits and for this is suitable, so much for mid waves, what for the low waves, up to the 40 MHZ. The gain his it is the order 20db and it consumes 7mA, when it is supplied with 12 until 15V dc. His entry and the exit are adapted with coaxial cable, complex resistance 75ohm. ..

100W FM Linear Amplifier

100W FM Linear Amplifier

This Power amplifier is equiped with a bipolar transistor,the famous MRF317. As lots of FM amplifier application ,the power transistor is in a C class bias. All the impedance networks (Input & Output) have been determined by using the software: Mimp.EXE. A 9 elements low pass filter ensures that we meet at least a 60 dB rejection from the carrier.(RF Simulation with RFSIM99). The FM amplifier has a 10 dB gain with a 60 to 65% efficiency. The Input VSWR is around 1.4 and there's no problem to reach the max power in all the FM band.. ..

30 Watt FM Linear amplifier with Mosfet BLF245

30 Watt FM Linear amplifier with Mosfet BLF245

The achievement of this 30 watt amp was thought to take place on a heatsink microprocessor PC. Equipped with its fans, the advantage of this method of cooling was chosen for the fact it is common and not very expensive. The size of the printed circuit will adapt quite easily to the type of sink that you have available, nine if possible, because often, those of recovery, the fans have already lived and the price of a new model remains very affordable. The amplification mode is class AB. Below is a description of the mounting frame. Ground planes are made of carnations, but it is also possible to achieve with simple crossings "legs of resistors," for example .. The circuit will be constructed from glass epoxy double-sided, 0.8 mm thick. The dimensions of the circuit must be respected at best, due to the presence of lines granted "strip-line. These dimensions are 73 mm wide and 63 mm in height...

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