Difference between revisions of "RF Attenuators"

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[[file:Atten_30dB_20dV_P1812-720px.jpg]]
 
[[file:Atten_30dB_20dV_P1812-720px.jpg]]
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== Attenuators ==
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[[file:Chart_mW_vs_dbM.PNG]]
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=== 30 dB Attenuator ===
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* [http://leleivre.com/rf_pipad.html Pi Attenuator Calculator]
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[[file:Atten30dB_P116-720px.jpg]]
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[[file:30dB_Attenuator.PNG]]
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* Built
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** Standard 5% resistor values
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** R1 = 820 in parallel with 22K = 790.6 ohms
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** R2 = 2 paralleled 120 Ohm 1/4W resistors paralleled with 470 ohms = 53.2 ohms
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** Flat from 0-30 MHz
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** Measured attenuation is flat
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*** -30.01dB at 1 MHz
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*** -30.24dB at 30 MHz
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** Input Impedance - 53.1 ohms, 21.3nF
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** SWR 1.06
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** 1/2W max (5VDC max, 0 ohm source)
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* NanoVNA scan data
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[[file:30dB_Attenuator_NanoVNA_Setup_Curve_900MHz.PNG]]
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[[file:30dB_Attenuator_NanoVNA_Data_900MHz.PNG]]
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* LTSPICE Simulation
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[[file:LTSPice_30dB.PNG]]
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=== 20 dB Attenuator ===
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[[file:Atten_20dB_P115-720px.jpg]]
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[[file:20dB_Attenuator.PNG]]
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* Build
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** Standard 5% resistor values
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** R1 = 2 of 510 in parallel also in parallel with 8.2K = 247.3 ohms
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** R2 = 2 paralleled 150 Ohm 1/2W resistors paralleled with 330 ohms = 61.11 ohms
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** Flat from 0-30 MHz
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** Measured attenuation is flat
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** Input Impedance - tbd ohms, tbd nF
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** SWR tbd
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** 1W max (8.6 V max, 0 ohm source)
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[[file:20dB_Attenuator_NanoVNA_Setup_Curve_900MHz.PNG]]
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[[file:20dB_Attenuator_NanoVNA_Data_900MHz.PNG]]
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* LTSPICE Simulation
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[[file:LTSPice_20dB.PNG]]
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=== 10 dB Attenuator ===
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[[file:Atten_10dB_P115-720px.jpg]]
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[[file:10dB_Attenuator.PNG]]
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* Build
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** Standard 5% resistor values
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** R1 = 2 of 150 in parallel also in parallel with 1.5K = 71.43 ohms (0.3% error)
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** R2 = 3 of 330 Ohm 1/4W parallel resistors paralleled with 810 ohms = 96.85 ohms (0.62% error)
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** Flat from 0-30 MHz
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** Measured attenuation is flat
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** Input Impedance - tbd ohms, tbd nF
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** SWR tbd
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** 3/4W max (9.1 V max, 0 ohm source)
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[[file:10dB_Attenuator_NanoVNA_Setup_Curve_900MHz.PNG]]
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[[file:10dB_Attenuator_NanoVNA_Data_900MHz.PNG]]
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* LTSPICE Simulation
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[[file:LTSPice_10dB.PNG]]
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=== Attenuator Construction ===
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* Single side copper clad PCB
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** Approx 2"x1"
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* Clean with steel wool
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* Solder SMA connectors
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** Use large alligator clips to hold while soldering
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** Solder on sides only
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[[file:Atten_01_SMAs_720px.jpg]]
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* Cut "T" Shaped pads
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** I used nibbler
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* Center fits between connector ground pins
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* Glue down pads with Superglue
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[[file:Atten_02_Pads_720px.jpg]]
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* Solder center pin with big solder blob
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** A bit too high for direct contact
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* Verify raised pad does not short to ground
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[[file:Atten_03_Solder CenterPads_720px.jpg]]
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* Solder side resistor(s)
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* Leave room for center resistor(s)
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[[file:Atten_04_Solder Side_Resistors_720px.jpg]]
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* Measure side resistors from pad to ground
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* Should match value
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* Solder center resistor(s)
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[[file:Atten_05_Solder Center_Resistors_720px.jpg]]
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* Verify no shorts between centers and ground

Revision as of 11:45, 7 September 2021

Homebrew Attenuators

Atten 30dB 20dV P1812-720px.jpg

Attenuators

Chart mW vs dbM.PNG

30 dB Attenuator

Atten30dB P116-720px.jpg

30dB Attenuator.PNG

  • 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

30dB Attenuator NanoVNA Setup Curve 900MHz.PNG

30dB Attenuator NanoVNA Data 900MHz.PNG

  • LTSPICE Simulation

LTSPice 30dB.PNG

20 dB Attenuator

Atten 20dB P115-720px.jpg

20dB Attenuator.PNG

  • 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)

20dB Attenuator NanoVNA Setup Curve 900MHz.PNG

20dB Attenuator NanoVNA Data 900MHz.PNG

  • LTSPICE Simulation

LTSPice 20dB.PNG

10 dB Attenuator

File:Atten 10dB P115-720px.jpg

10dB Attenuator.PNG

  • 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

LTSPice 10dB.PNG

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

Atten 01 SMAs 720px.jpg

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

Atten 02 Pads 720px.jpg

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

Atten 03 Solder CenterPads 720px.jpg

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

Atten 04 Solder Side Resistors 720px.jpg

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

Atten 05 Solder Center Resistors 720px.jpg

  • Verify no shorts between centers and ground
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