Homebrew RF Attenuators

Homebrew RF Attenuators

30 dB Attenuator

• Pi Attenuator Calculator

• Built
  • Standard 5% resistor values
  • R1 = 820 in parallel with 22K = 790.6 ohms
  • R2 = 2 paralleled 120 Ohm 1/4W resistors paralleled with 470 ohms = 53.2 ohms
  • Flat from 0-30 MHz
  • Measured attenuation is flat
    • -30.01dB at 1 MHz
    • -30.24dB at 30 MHz
  • Input Impedance - 53.1 ohms, 21.3nF
  • SWR 1.06
  • 1/2W max (5VDC max, 0 ohm source)

• NanoVNA scan data

• LTSPICE Simulation

20 dB Attenuator

• Build
  • Standard 5% resistor values
  • R1 = 2 of 510 in parallel also in parallel with 8.2K = 247.3 ohms
  • R2 = 2 paralleled 150 Ohm 1/2W resistors paralleled with 330 ohms = 61.11 ohms
  • Flat from 0-30 MHz
  • Measured attenuation is flat
  • Input Impedance - tbd ohms, tbd nF
  • SWR tbd
  • 1W max (8.6 V max, 0 ohm source)

• LTSPICE Simulation

Attenuator Construction

• Single side copper clad PCB
  • Approx 2"x1"
• Clean with steel wool
• Solder SMA connectors
  • Use large alligator clips to hold while soldering
  • Solder on sides only

• Cut "T" Shaped pads
  • I used nibbler
• Center fits between connector ground pins
• Glue down pads with Superglue

• Solder center pin with big solder blob
  • A bit too high for direct contact
• Verify raised pad does not short to ground

• Solder side resistor(s)
• Leave room for center resistor(s)

• Measure side resistors from pad to ground
• Should match value
• Solder center resistor(s)

• Verify no shorts between centers and ground