RF Attenuators
Contents
Attenuator Charts
Homebrew RF Attenuators
30 dB Attenuator
- 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
10 dB Attenuator
File:Atten 10dB P115-720px.jpg
- Build
- Standard 5% resistor values
- R1 = 2 of 150 in parallel also in parallel with 1.5K = 71.43 ohms (0.3% error)
- R2 = 3 of 330 Ohm 1/4W parallel resistors paralleled with 810 ohms = 96.85 ohms (0.62% error)
- Flat from 0-30 MHz
- Measured attenuation is flat
- Input Impedance - tbd ohms, tbd nF
- SWR tbd
- 3/4W max (9.1 V max, 0 ohm source)
File:10dB Attenuator NanoVNA Setup Curve 900MHz.PNG
File:10dB Attenuator NanoVNA Data 900MHz.PNG
- 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
References
- Heavily inspired by Alan (W2AEW) video