RF Attenuators

Purchased Attenuators

Programmable Attenuator

• PE4302 RF Attenuator board in my enclosure design

Triple Attenuator

• 0/10/20/30 dB Attenuator

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

Attenuator Design - Rev 2

• SMA connectors
• Resistors
  • 1206
    • 1/4W
  • 1% values

Parts

Mfr. #	Manufacturer	Customer #	Qty	R1/R2	Description
RK73H2BTTE17R8F	KOA Speer	ATTEN_03DB	1	R1	Resistors - SMD 1/4W 17.8 ohms 1%
RC1206FR-07294RL	YAGEO	ATTEN_03DB	2	R2	Resistors - SMD 294 ohms 1/4W 1206 1%
RK73H2BTTD37R4F	KOA Speer	ATTEN_06DB	1	R1	Resistors - SMD 1/4W 37.4 ohms 1%
CRCW1206150RFKEAC	Vishay	ATTEN_06DB	2	R2	Resistors - SMD 1/4Watt 150 ohms 1%
RC1206FR-0771R5L	YAGEO	ATTEN_10DB	1	R1	Resistors - SMD 71.5 ohms 1/4W 1206 1%
RC1206FR-0797R6L	YAGEO	ATTEN_10DB	2	R2	Resistors - SMD 97.6 ohms 1/4W 1206 1%
RK73H2BTTD1070F	KOA Speer	ATTEN_13DB	1	R1	Resistors - SMD 1/4W 107 ohms 1%
RC1206FR-0778R7L	YAGEO	ATTEN_13DB	2	R2	Resistors - SMD 78.7 ohms 1/4W 1206 1%
AC1206FR-07249RL	YAGEO	ATTEN_20DB	1	R1	Resistors - SMD 249 ohms 1/4W 1206 1%
RK73H2BTTDD61R9F	KOA Speer	ATTEN_20DB	2	R2	Resistors - SMD 61.9 ohms 1%
RK73H2BTTD7870F	KOA Speer	ATTEN_30DB	1	R1	Resistors - SMD 1/4W 787 ohms 1%
AC1206FR-0753R6L	YAGEO	ATTEN_30DB	2	R2	Resistors - SMD 53.6 ohms 1/4W 1206 1%
RC1206FR-072K49L	YAGEO	ATTEN_40DB	1	R1	Resistors - SMD 2.49k ohms 1/4W 1206 1%
RK73H2BTTD51R0F	KOA Speer	ATTEN_40DB	2	R2	Resistors - SMD 1/4W 51 ohms 1%
RK73H2BTTDD49R9F	KOA Speer	ATTEN_50_60DB	2	R2	Resistors - SMD 49.9 ohms 1%
RC1206FR-077K87L	YAGEO	ATTEN_50DB	1	R1	Resistors - SMD 7.87k ohms 1/4W 1206 1%
RC1206FR-0726K1L	YAGEO	ATTEN_60DB	2	R2	Resistors - SMD 26.1k ohms 1/4W 1206 1%

Measurements

• NanoVNA
• S21 gain
• 1-900 MHz scan
• Calibrated with cable on thru

40 dB Attenuator

• Flat from 1-600 MHz
• Higher attenuation past 600 MHz
• -39.9 dB at 14 MHz
• S21

• Flat from 1-30 MHz
• S21

• s11
• 1-900 MHz

• VSWR
• 1-900 MHz

DC Block

• Use same PCB
  • Install 0.1uF cap between the two SMAs
• S21 of -0.8 dB at 50 KHz
• S21 of 0.44 dB at 900 MHz

Attenuator Charts

References

• Attenuator Calculator - Le Leivre.com
• Attenuator Calculator - Pasternak

• Heavily inspired by Alan (W2AEW) video