Description
Sold as a kit; assembly is required. Please consult the table below for the component layout. Capacitors are 1206 size SMD. This size is reasonable for hand soldering. All supplied magnet wire (0.3 mm) is solder heat stripable. Improved assembly and technical documentation is coming soon.
T30 Size
| Band | Passband Attenuation | 2nd Harmonic Attenuation | 3rd Harmonic Attenuation | C1 (pF) | C2 (pF) | C3 (pF) | C4 (pF) | L2 | L1 | Toroid |
|---|---|---|---|---|---|---|---|---|---|---|
| 6m | TBD | TBD | TBD | 68 | 120 | 68 | 10 | 10 turns (180nH) | 12 turns (260nH) | T30-17 (blue/yellow) |
| 10m / 12m / 15m | <0.9 dB | 50 dB / 31 dB / 18 dB | 47 dB / 46 dB / 50 dB | 100 | 180 | 82 | 22 | 13 turns (270nH) | 14 turns (314nH) | T30-17 (blue/yellow) |
| 17m / 20m | <0.7 dB | 40 dB / 22 dB | 54 dB / 62 dB | 180 | 330 | 180 | 27 | 16 turns (410nH) | 18 turns (520nH) | T30-17 (blue/yellow) |
| 30m / 40m | <1 dB | 39 dB / 15 dB | 40 dB / 37 dB | 270 | 470 | 180 | 82 | 23 turns (850nH) | 25 turns (1000nH) | T30-17 (blue/yellow) |
| 60m / 80m | <0.8 dB | 43 dB / 14 dB | 55 dB / 43 dB | 680 | 1200 | 680 | 100 | 21 turns (1.59uH) | 23 turns (1.90uH) | T30-6 (yellow) |
Features
Designed with compact size, low weight, and ease of deployment in mind, these filters are ideal for portable amateur radio operations, including SOTA, and POTA.
- Most of these filters use the component values provided by the QMX assembly manual.
- Attenuation measurements are from NanoVNA (see picture gallery).
- The shape of the frequency response will be verified with an oscilloscope. However, the attenuation values from the oscilloscope are less accurate due to losses in the measurement setup. I would trust the VNA’s values more.
- Additional testing and characterization are in progress. More detailed test results will be added as they become available.
- My LPF bypass modification for the QMX will provide 80m–6m operation with three of these filters for any of the available band versions.
Important Information
- Kit is sold unassembled. Assembly is required.
- Component layout is provided in the table.
- Documentation is currently being improved and expanded.
- Components may vary from images due to availability.
- No returns on assembled kits.
- Shipping is limited to the lower 48 United States.
- Contains lead.
These filters are designed with portable operation in mind and prioritize small size, light weight, and quick deployment. They are a great option for operators looking to add external harmonic filtering to a compact or portable station.
Designed and sold by AD8C
The Fine Print
Use at Your Own Risk: This is an independent project and is provided as-is. This kit is intended for educational, evaluation, or hobbyist assembly. By purchasing and assembling this board, you accept all risks. The creator/seller accepts no liability from the use or misuse of this product.
Trademark Notice: QMX is a registered trademark of QRP Labs. This project is entirely independent and is not affiliated with, authorized, or endorsed by QRP Labs.
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