RF-Amp

RF Amplifier Features

• From Charlie Morris' (ZL2CTM) Go QRP Portable SSB Rig
  • Solid State Design for the Radio Amateur?
• +22 dB gain
• Input connectors: SMA or BNC
• 49x49mm card
• 4x 4-40 mounting holes

RF Amplifier Design

Schematic

DC Operating Point

• Ice = 10 mA
• Ve = 0.1 * Vcc = 1.2V

Input/Output Transformer

FT37-43 Toroid

• FT37-43
• Wideband Transformers 5 - 400 MHz
• Power Transformers 0.5 - 30 MHz
• 10 turns = 35uH

Tracks

Input Transformer

• • Input Transformer (T1 on Charlie's - T2 on this board)
    • 50:75.8 Ohms = 1 : 1.23 turns ratio
      • 9 turns primary, 11 turns on secondary

Output Transformer

• • Output transformer (T2 on Charlie's - T1 on this board)
    • 200:50 Ohms = 2:1 turns ratio
    • 10 turns primary (on transistor collector), 5 turns secondary (towards output)

LT Spice Simulation

• LTspice Simulation - GitHub source file

Transformers

Charlie Morris Schematics

• From Charlie Morris' (ZL2CTM) Go QRP Portable SSB Rig

IF AMP

From Charlie's notes with mods for my use

Beta DC

= Geometric mean min/max beta at operating current from 2N3904 data sheet

• • = sqrt(100*300) = 173

Beta AC

• Gain bandwidth product divided by operating frequency
  • Assume operating frequency of 10 MHz (my IF is actually at 9 MHz)
  • = 300/10 = 30

DC Operating Point

• CE current 10 mA
  • V(emitter resistor) = 1/10 Vcc = 1.2V
    • R(emitter resistor) = 1.2V/0.01A = 120 ohms
• VCE = 0.7V
• V(emitter) = 1.2V
• V(base) = V(emitter) + VCE = 1.9V
• Assume current in biasing resistors = 10x current needed by DC beta
  • 10 mA in C-E, beta DC less = 10 mA/173 = 48 uA
  • 10x the current in the biasing resistors = 480 uA
• R2 is 1.9V at 480 uA = 3.9K use 3.3K
• R1 sources current to R2 and BE junction
  • Voltage = Vcc (12V) - 1.9V = 10.1V
  • Current = 480 uA + 48 uA = 528 uA
  • R1 = 10.1 / .528 mA = 19K, use 15k
• Input resistance - parallel resistors R1, R2 paralleled with transistor input impedance
  • R1=15K, R2=3.3K
  • Transistor resistance = Beta AC (30) times re
    • re = 26 / Ie (10 mA in mA) = 26/10 =
    • Beta AC * re = 30*2.6 = 78 ohms - predominates
  • All in parallel are 75.8 ohms

Transformers

• T1 50:75.8 ohms
  • n = sqrt(Zout/Zin) = sqrt(75.8/50) = 1.23
  • 9:11 turns ratio
• T2 - different than Charlie's design since my Crystal filters are all 50 ohms in/out
  • 250:50 ohms
  • n = sqrt(250/50) = 2.23:1
  • 11:5 turns

Assembly Sheet

• RF Amplifier Assembly Sheet