Crystal Filter Design

Design

• Butterworth, Chebyshev filters
• Narrow bandwidth bandpass filters for CW or SSB
• 9 MHz nominal frequency
• Several crystal filer designs
• Bin crystals using Colpitts Crystal Oscillator
  • Hand select close values from a pile of crystals
  • Can get much closer than 10% of bandwidth with 50 crystals

W7ZOI Filters

• 9 MHz Filters With Inexpensive Crystals - W7ZOI paper

CW3 Crystal Filter on Kits and Parts Board

• 9 MHz nominal
• Measured values
  • 8.997836
  • 8.997836
  • 8.997838

• 330 Hz bandwidth
• Built onto Kits and Parts board

• Schematic from W7ZOI paper

• W7ZOI Measurements

• Modified K&P schematic

• K&P Board

• NanoVNA Capture / Analysis

• Bandwidth
  • 400 Hz -3dB measured
  • 600 Hz -6dB measured

CW 5 Crystal Filter on Kits and Parts Board

• 9 MHz nominal
• Measured values
  • 8.997782
  • 8.997783
  • 8.997784
  • 8.997784
  • 8.997785
• 500 Hz bandwidth
• Built onto Kits and Parts board

• Schematic from W7ZOI paper

• W7ZOI Measurements

• XF2 Modifications

• K&P Board
  • Cut etch from X2 to X3
  • Cut etch from X4 to X6
  • Add wire across C1
  • Add wire across C8

• NanoVNA Capture / Analysis

CW3 VS CW5 Filter Comparison

• 5 KHz span
• 5 Crystal filter is wider in bandpass but has sharper skirts than the 3 crystal filter

SSB 4 Crystal Filter on Kits and Parts Board

• 9 MHz nominal
• Measured values
  • 8.997800
  • 8.997801
  • 8.997802
  • 8.997803
• 2KHz bandwidth
• Built onto Kits and Parts board

• Schematic from W7ZOI paper

• W7ZOI Measurements

• XF2 Modifications

• K&P Board
  • Cut etch from X1 to X2
  • Add wire across C1
  • Add wire across C8
  • Add wire across C9
  • Install X1 at X1a position

• NanoVNA Capture / Analysis

SSB 6 Crystal

References

• Crystal ladder filters – Software
• Crystal Ladder Filters for All - ARRL QEX
• DISHAL software by DJ6EV
• A Practical Test Set for Comprehensive Crystal Testing
• Crystal characterization and crystal filter design
• Crystal parameters Written by Hans Summers

Kits and Parts dot Com Crystal Filter Kit

• Kits and Parts dot Com Crystal Filter

Schematic

PCB

Notes

• T1 & T2 are optional matching transformers.
• Typical transformer type will be a BN-43-2402 using 34 gauge magnet wire
• C3a,C4a,C5a,C6a are optional trimmer capacitors for fine tuning the crystal filter
• Typical trimmer caps are GKG50015

Sorted 9 MHz Crystals

• Bought 50 crystals
• Marked with numbered labels
• Mouser #: 449-LFXTAL064523BULK
• Mfr. #: LFXTAL064523Bulk
• Mfr.:IQD
• Description: Crystals 9MHz 30pF -10C 60C
• Datasheet

Number	Freq	Delta Freq	Abs delta f
33	8.997668	-130.7	130.7
43	8.997704	-94.7	94.7
17	8.997707	-91.7	91.7
42	8.997707	-91.7	91.7
40	8.997726	-72.7	72.7
03	8.997733	-65.7	65.7
36	8.997742	-56.7	56.7
23	8.997753	-45.7	45.7
25	8.997755	-43.7	43.7
05	8.997761	-37.7	37.7
27	8.997767	-31.7	31.7
15	8.997776	-22.7	22.7
39	8.997782	-16.7	16.7	CW5
35	8.997783	-15.7	15.7	CW5
10	8.997784	-14.7	14.7	CW5
18	8.997784	-14.7	14.7	CW5
04	8.997785	-13.7	13.7	CW5
20	8.997788	-10.7	10.7
49	8.997788	-10.7	10.7
09	8.997791	-7.7	7.7
12	8.997791	-7.7	7.7
41	8.997793	-5.7	5.7
06	8.997794	-4.7	4.7
21	8.997798	-0.7	0.7
38	8.997798	-0.7	0.7
07	8.997800	1.3	1.3
32	8.997800	1.3	1.3	SSB4
14	8.997801	2.3	2.3	SSB4
47	8.997802	3.3	3.3	SSB4
34	8.997803	4.3	4.3	SSB4
08	8.997809	10.3	10.3
30	8.997810	11.3	11.3
48	8.997812	13.3	13.3
50	8.997814	15.3	15.3
31	8.997818	19.3	19.3
46	8.997822	23.3	23.3
22	8.997825	26.3	26.3
26	8.997836	37.3	37.3	CW3
44	8.997836	37.3	37.3	CW3
28	8.997838	39.3	39.3	CW3
02	8.997840	41.3	41.3
45	8.997840	41.3	41.3
29	8.997846	47.3	47.3
19	8.997851	52.3	52.3
01	8.997858	59.3	59.3
24	8.997858	59.3	59.3
11	8.997868	69.3	69.3
16	8.997872	73.3	73.3
13	8.997879	80.3	80.3
37	8.997937	138.3	138.3
Average	8.997799	Deviation	36.34

Videos

Charlie Morris

• Jan '21 - Simple SSB Rig: Part 3 - Crystal Filter

• Mar '20 - CW Rig. Part 1 - Homebrew CW Crystal Filter

• Aug '18 - Homebrew 80/40m SSB/CW Rig - #4b CW Crystal Filter

• Jan '18