Kits and Parts Lowpass Filter

Kits and Parts Universal Filter Board

• 7-pole Universal Low Pass Filter for HF - Kits and Parts webpage
  • $4 PCB
  • Handles toroid inductor sizes up to T80
    • 125W power
  • 0.2" lead spacing for caps
  • (4) 4-40 mounting holes

CWAZ filter

• 2nd-Harmonic-Optimized LPFs by By Ed Wetherhold, W3NQN
  • Much better performance than standard 3C/3L filter at 2nd harmonic
  • Only needs one additional capacitor across center inductor
  • Other L/C values are a bit different to compensate

Other References and Topologies

• Introduction to LPFs by Paul Hardin, NA5N
• 7 Element Chebyshev standard value capacitor LPFs
• LC Filter Design Tool
• Toroid Coil Winding Calculator

K&P Schematic

K&P PCB

CWAZ 40M, 7 MHz Filter

• Based on 2nd-Harmonic-Optimized LPFs by By Ed Wetherhold, W3NQN - Built this one

SPICE Simulation

• GitHub repo
• -6 dB at 7 MHz
• -68 dB at 1st harmonic (14 MHz)
• -75 dB at 2nd harmonic (21 MHz)

T37-2 Inductors

• T37-2 Toroid Specs and turns calculator

INDUCTANCE - L1, L3

• Desired: 1.34 uH
• Calculated: 1.3 uH (97% of desired) Turns required: 18
• CORE
• Part number: T-37-2 (Red)
• Frequency Range: 1 to 30 MHz
• u: 10
• AL: 40 uH/100 turns

INDUCTANCE - L2

• Desired: 1.22 uH
• Calculated: 1.2 uH (95% of desired) Turns required: 17
• CORE
• Part number: T-37-2 (Red)
• Frequency Range: 1 to 30 MHz
• u: 10
• AL: 40 uH/100 turns

Measured on NanoVNA

• 7 MHz LP filter
• Built with junk box low voltage ceramic disc caps

Rebuild - Higher Power

• T80-2 Inductors
  • Larger gauge wire
  • Integer turns values
  • T80-2 Toroid Specs and turns calculator

Simulation

Measured with NanoVNA

• Excellent performance!!!
• 7 MHz
  • S21 = -1.55 dB
  • VSWR = 1.008
• 14 MHz - 1st harmonic
  • S21 = -55.8 dB
  • VSWR = 5.181
• 21 MHz - 2nd harmonic
  • S21 = -69 dB
  • VSWR = 15.225

CWAZ - 20M, 14MHz LP Filter

• SPICE Simulation

• Toroid T80-2

• T80-2 has Optimum Resonant Circuit Range for highest Q and lowest core loss
  • 250 KHz - 10 MHz
• T80-6 has better characteristics
  • Optimum Resonant Circuit Range for highest Q and lowest core loss
  • 3 MHz - 40 MHz
• Don't have any T80-6 but I do have T37-6

NanoVNA caps

Ceramic Disc Caps

• High voltage quality caps
  • Ceramic - should these be silver mica caps?
  • Ceramic caps are 10x cheaper than silver mica caps
    • 100pF, Silver Mica cap, P/N: CDV16FF101JO3F, $1.40 (per, qty 10)
    • 100pF, Ceramic cap, P/N: CC45SL3AD101JYNNA, $0.14 (per, qty 10)
  • Will the ceramic caps cause Microphonics or is that only an issue in gain stages?
    • SL caps are single layer

Capacitance (pF)	Mfr. #	Manufacturer	Description
10	S100K33SL0R63K7R	Vishay	Ceramic Disc Capacitors 10pF 3000V 10% SL0 7.5mm LS
33	CC45SL3AD330JYNNA	TDK	Ceramic Disc Capacitors D: 5.5mm 1kV 33pF SL 5% LS:5mm
47	CC45SL3AD470JYVNA	TDK	Ceramic Disc Capacitors D: 5.5mm 1kV 47pF SL 5% LS:5mm
82	CC45SL3AD820JYNNA	TDK	Ceramic Disc Capacitors D: 6mm 1kV 82pF SL 5% LS:5mm
100	CC45SL3AD101JYNNA	TDK	Ceramic Disc Capacitors D: 6.5mm 1kV 100pF SL 5% LS:5mm
120	CC45SL3AD121JYNNA	TDK	Ceramic Disc Capacitors D: 7mm 1kV 120pF SL 5% LS:5mm
200	S201K33S3NN63L6R	Vishay	Ceramic Disc Capacitors 200PF 1KV 10%
270	CC45SL3AD271JYVNA	TDK	Ceramic Disc Capacitors D: 9mm 1kV 270pF SL 5% LS:5mm
330	S331K33Y5PR63K7R	Vishay	Ceramic Disc Capacitors 330pF 3000V 10% Y5P 7.5mm LS
390	CC45SL3AD391JYVNA	TDK	Ceramic Disc Capacitors D: 10.5mm 1kV 390pF SL 5% LS:5mm
470	D471K20Y5PH6UJ5R	Vishay	Ceramic Disc Capacitors 470pF 100V 10%
680	S681K29Y5PN63J5R	Vishay	Ceramic Disc Capacitors 680pF 1000V 10% Y5P 5.0mm LS