RF Pre Amplifier | Electronic Project Circuits

Posts Tagged ‘RF pre amplifier’

RF power amplifier 80W by C2782

This is a pretty conventional design, using bipolar transistors in a tuned class C circuit. Thanks to the use of two stages, the amplifier can be driven to full power with less than 1 watt driving power, so that a large gain margin results in this transmitter.

Bipolar VHF power transistors have a severe affinity for low frequency self-oscillation. To obtain stability in this amplifier, I employed several techniques, such as placing the resonances of base and collector chokes far apart, damping the chokes with resistors, using RC combinations for absorption of unwanted frequencies, using feedtrough capacitors for bypassing on the board, etc. It took some tweaking, but the amplifier ended up unconditionally stable.

The impedance matching network between the two transistors calls for such a low inductance, that it would be impractical to make it with actual wire. So I used a micro stripline etched on the PCB. Also, the power and SWR sensor at the output was made with micro striplines.

Read More Source:http://ludens.cl/Electron/fmtx/fmtx.html
Thank you.

Be the first to comment - What do you think? Posted by admin - January 30, 2008 at 10:06 am

Categories: RF-Radio Frequency Tags: FM amplifier, RF amplifier, RF pre amplifier

RF Preamplifier by 2N2219a , 2N4427 , 2N3553

Input needs only several mWatts (e.g. BF900) -> 300 mWatts OUT. This schematic is a often used buffer. It’s easy to build, clean and cheap. When you want even more power, you can replace the 2N2219a by a 2N4427 or 2N3553. You can lower the output by adding a little resistor (10..47 Ohm 1/2W) in the emitter line of the 2N2219a.

Read More Source:http://www.pulsarfm.nl/buffer1.htm

Be the first to comment - What do you think? Posted by admin - January 15, 2008 at 10:05 pm

Categories: Pre Amplifier, RF-Radio Frequency Tags: 2N3553, RF pre amplifier

SW RF Pre-Amplifier with 2N3819

A radio frequency amplifier to boost SW reception. Frequency range approximately 5 to 20 MHz.

Parts List:
R1 100k
R2 1k
R3 330
R4 47k
R5 68k
R6 4.7k
VR1 4.7k
C1 100n
C2 220p
C3 100n
C4 1n
C5 10n
VC1 500pF
L1 2.5m
J1 2N3819
Q1 BC108B

The problem with amplifying weak radio signals is that you also amplify the noise. What you can receive depends on how much background noise is present, whether it be man made interference or static. In this design the RF signal is first met by a resistive attenuator, this is necessary as strong signals could otherwise overload your receiver. The transformer T1 is would on a 1 inch diameter ferrite loop. The primary (antenna side) is 2 turns of 22 swg wire. The secondary is 4 turns of 22 swg wire. The 4 turns are spaced to occupy roughly half the coils circumference. The approximate inductance of the secondary is 20uH. To cover 5 to 20 Mhz a capacitor tuning from around 3pF to 200pF is required. A standard capacitor of 400 or 500pF (full mesh) can be used by including a series capacitor, C2 in the above Capacitors. Capacitors in series behave the same as resistors in parallel. The smallest capacitance is just less than the smallest capacitor in series and highest value also less than the highest capacitance. With a 220pF capacitor for C2 and a 500pF variable capacitor (that tunes down to 5pF) the effective capacitance tunes 143pF to about 4.8pF. This is roughly correct and not critical as the gain of the FET will amplify frequencies outside the tuned circuit range. The 2N3819 FET operates in common source. The series base resistor R1 is included to even out the response, the internal gate source impedance is thus increased by R1 at higher frequencies. The drain circuit includes a 2.5mH choke. A 4.7mH can also be used. As the Q factor of these coils are high, a series resistor R3 is introduced to flatten the response. The frequency response is shown below calculated at 10% increments of VC1:

Circuit : Andy Collinson
Email: anc@mitedu.freeserve.co.uk
Source: http://www.zen22142.zen.co.uk/Circuits/rf/swrfamp.htm