Kits and Parts Universal Wideband Small Signal RF Amplifier

Specs

• Kits and Parts Universal Wideband Small Signal RF Amplifier
• 22+ dBm power gain from 2-30 MHz
  • Measured +25-27 dBm gain - fairly flat response
  • +20 dBm gain up to 80 MHz
• 50 ohm input and 50 ohm output.
• 100 milliwatt maximum output.
• 0.031A at 12V = 370mW

Schematic

• 2SC5551A Datasheet

Transformer

• FT37-43 Toroid

LTSPICE Simulation

• 2SC5551A LTSPICE Model

.model 2SC5551A NPN(IS=4.58f BF=150 NF=1.003 VAF=35 IKF=1.2 ISE=5f NE=1.6 BR=35 NR=1.001 VAR=20 IKR=10.98m ISC=255.9f NC=1.5 RB=1.5 IRB=300.0m RBM=300m RE=280m RC=1.25 XTB=0 EG=1.11 XTI=3 CJE=2.36p VJE=199.0m MJE=73.20m TF=30.50p XTF=13.45m VTF=280.0m ITF=25.80m PTF=25.7 CJC=3.08p VJC=520.0m MJC=380.8m .15m TR=1.38n FC=1.51m )

• Without transformer

• With transformer

PCB

Build Instructions

1. Align the SMD 2SC5551A RF Transistor onto Q1 pad in the center of the PCB. Using a temperature controlled solder pencil, solder without overheating.
2. Align the four 100n SMD capacitors on the PCB and solder.
3. Install resistors R1, R2, R3 and R4 on the PCB and solder.
4. Install Toroids Transformer T1, Twist the Red & Green wires together to about 4 twists per inch. Wind 10 turns of the twisted wires onto the toroid. The magnet wire is heat stripable; trim each wire end to 3/4 inches. Prepare the toroid wires for soldering.
5. Magnet Wire Soldering Details Here: One of each colored wires connects under the toroid and one of each colored wires connects on the outside of the toroid. One color wire should connect to J3/C4 and the other color connects to Q1. You should also have 2 different color wires connecting under the toroid via a PCB trace.
6. R5,6,7 (not included) are used to attenuate the rf output. Place a jumper wire across R6.
7. Connect the RF Amplifier via J1(input), J2(output) and J3(power).

NanoVNA Measurements

• Tried 30 dB Attenuator in and out sides of RF Amplifier with different results

Attenuator Before Amp

• NanoVNA
  • Sweep settings, Attenuator in port CH1 (s21) in dB: 30.0
• Attenuator - 30 dB
  • Below are with 30 dB attenuator between NanoVNA CH0 (output) and RF Amp input
• Built four Amplifiers, identical results

At 1, 9 and 30 MHz

• 30 dB attenuator between NanoVNA CH0 (output) and RF Amp input

S21 Gain

• 30 dB attenuator between NanoVNA CH0 (output) and RF Amp input

SWR

• 30 dB attenuator between NanoVNA CH0 (output) and RF Amp input
• Very good match into attenuator (as would be expecteed)

Attenuator After Amp

• 30 dB attenuator between NanoVNA CH0 (output) and RF Amp input
• 20 dB gain at 80 MHz

At 1, 9 and 30 MHz

• NanoVNA
  • Repeated with 30 dB attenuator between RF Amp output and the NanoVNA CH1 (input)
• Attenuator - 30 dB

S21 Gain

SWR

Key Point data

1-300 MHz

References

• PI Attenuator Calculator
• Pi Attenuator Calculator