4W HF Bands QRP RF Linear Amplifier

HF Bands QRP RF Linear Amplifier based power transistor 2N5590.

This is a rather unusual QRP power RF 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.

This PA will deliver 4 watts continuously (with a suitable heatsink), and may be loaded into a short-circuit or open circuit without causing damage. This makes it almost the ideal PA for outdoor/field use. Above is the full circuit diagram of the RFPA and the coil winding pattern. This PA may be used for for SSB, as well as CW (and AM?).

Set RV1 to MINIMUM resistance and apply 12volt power supply with NO DRIVE. Adjust RV1 for about 250mA DC total supply current. This may be be reduced to a much smaller current if lower output powers (reduced drive) is used.

RF Amplifier VHF FM 87.5- 108 MHz based MOSFET BLF245

This is the RF amplifier for VHF/FM range frequency of 87.5- 108 MHz. The circuit built using power transistor MOSFET BLF245.

The achievement of this 30W RF amplifier was designed 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 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.

Parts List:

C1,C4 = 47nF50v
C2,C8 = 4,7uF63v
C3,C5 = 22nF50v
C6,C7 = 1nF50v
C9 = 100nF50v
C10,C15 = 2,2nF
C11 = 27pF
C12,C18 = 82pF
C13 = 120pF
C14 = 8,2pF
C16 = 22pF
C17 = 47pF
D1,D2 = ZENER 3,9v
L1 = 2,4uH
L2 = 360nH
L3,L4,L5 = STRIP-LINE
Q1 = BLF245
R1,R3 = 5,6 Ohms
R2,R7 = 1,8Kohms
R4 = 6,8Kohms
R5,R6 = 10Kohms
R8,R9 = 12 Ohms
R10 = 220 Ohms
T1 = TRANSFO COAXIAL
T2 = TRANSFO 2x500nH

Visis this page for detailed explanation and tutorial of the RF amplifier circuit.

40Mhz RF Amplifier Circuit

This is the 40Mhz RF amplifier circuit. The sensitivity of a receiver may be significantly increased if this circuit is inserted between the receiver and the antenna. The amplifier circuit does not use resonant circuits and is suitable for both medium and for the short waves, up to 40 MHz.

The gain of this RF amplifier is 20db and it consumes 7mA electric current, when it is supplied with 12 until 15V dc. The input and the output should be connected with coaxial cable, resistance 75ohm.

Parts List:

R1 = 75ohm R2 = 10Kohm R3-7 = 5.6Kohm R4-5 = 4.7Kohm R6 = 820ohm R8 = 470ohm R9 = 2.2Kohm R10 = 68ohm

C1-3 = 47nF/100V C2-4 = 10nF/100V C5-6 = 47nF/100V Q1-2-3 = AF125 J1-2 = Jack BNC