Difference between revisions of "SSB6 Design"
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** Add SMA connectors | ** Add SMA connectors | ||
* Measured with 200 ohm resistors at input caps to ground | * Measured with 200 ohm resistors at input caps to ground | ||
| − | * Measure transformer | + | * Measure transformer impedances from NanoVNA |
| − | ** 48.9-j0.900 Ohms | + | ** Input |
| − | * VSWR 1:1.031 | + | *** 48.9-j0.900 Ohms |
| + | *** VSWR 1:1.031 | ||
| + | ** Output | ||
| + | *** 48.7-j0.714 Ohms | ||
| + | *** VSWR 1:1.031 | ||
* Flat over passband | * Flat over passband | ||
Revision as of 22:05, 17 October 2021
Contents
Design
- 6 element filter
- W7ZOI Crystal Filter paper has several crystal filter designs
- Narrow bandwidth bandpass filters for SSB
- Used for transmit/receive
- 9 MHz nominal frequency
- 50 Ohms in/out impedance
- 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 on Kits and Parts Boards
- Other filter builds
- 5 or less crystals
W7ZOI SSB6 Schematic
- Response curve
Build
- SSB6 filter is too big for Kits and Parts board (5 crystals limit)
- 2500 Hz bandwidth
Schematic
Dishal Values
- Impedance = 195.9
RefDes Dishal RefDes W7ZOI Ck12 87.3 C3/C9 82 Ck23 110.9 C4/C8 100 Ck34 114.4 C6 100 Cs1 110 C2/C10 120 Cs3 369.5 C5/C7 470
3D Image
Measured Crystal Values
- 6 crystals within 7 Hz of each other
- Selected from 50 purchased
Number Freq Delta from average 09 8.997791 -7.7 12 8.997791 -7.7 41 8.997793 -5.7 06 8.997794 -4.7 21 8.997798 -0.7 38 8.997798 -0.7
Enclosure 80x50x20
- Fits in 80x50 extruded enclosure
- Material: Aluminum
- Color: black
- Size: approx.80*50*20mm
- Thickness: approx.1mm
Performance Measurements
Overall
- NanoVNA
- 2.5 KHz / div
Detailed
- 1 KHz/div
- Bandpass looks about 2500 KHz = good
- Left freq = 8.99762 MHz
- Right freq = 9.00005 MHz
- Delta = 2.43 KHz
- Center frequency = 8.99885 MHz
- Implies crystals are properly matched?
- Insertion loss at "best" point (red marker) -5.14 dB = OK
- Deep skirts = good
- Ripple looks bad
- Right side low
Compared to SSB4
- Fcenter = 8.998MHz
- Span = 10KHz
- 1 KHz/div
- Skirts much deeper on SSB6 than SSB4
- -90 dB on SSB6 at window edges
- -60 dB on SSB4 at window edges
- Passband much flatter on SSB4
- Insertion loss lower on SSB4
- SSB4
Improvements
No impact
- Cleaned board
- Removed wires on transformer that were not clipped flush-ish
- No effect - same ripple, same drop at the right side, same insertion loss
Incremental Build
- Start with unpopulated board
- Add SMA connectors
- Measured with 200 ohm resistors at input caps to ground
- Measure transformer impedances from NanoVNA
- Input
- 48.9-j0.900 Ohms
- VSWR 1:1.031
- Output
- 48.7-j0.714 Ohms
- VSWR 1:1.031
- Input
- Flat over passband
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 (QRP Labs)
