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 (0.33 mm) is solder heat stripable. Improved assembly and technical documentation is coming soon.
| 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 | <1 dB | 50 dB / 31 dB | 47 dB / 46 dB | 100 | 180 | 82 | 22 | 13 turns (270nH) | 14 turns (314nH) | T30-17 (blue/yellow) |
| 15m / 17m / 20m | TBD | TBD | TBD | 180 | 330 | 180 | 27 | 16 turns (410nH) | 18 turns (520nH) | T30-17 (blue/yellow) |
| 30m / 40m | TBD | TBD | TBD | 270 | 470 | 180 | 82 | 23 turns (850nH) | 25 turns (1000nH) | T30-17 (blue/yellow) |
| 60m / 80m | TBD | TBD | TBD | 680 | 1200 | 680 | 100 | 21 turns (1.59uH) | 23 turns (1.90uH) | T30-6 (yellow) |
QMX Internal LPF Mod
Use pin 61 (LPF_5, an unused LPF output) of the STM32 on your QRP Labs QMX to switch in another LPF. This enables seamless operation with an additional LPF while preserving the QMX’s internal LPFs for normal operation. There’s no need to modify the internal LPFs.
This modification allows you to continue using your QMX normally while expanding its operating frequency range to one, two, or even three additional bands.
Installation
The mod fits entirely within the standard QMX enclosure.
This modification is specifically designed for the QMX and is rated for operation up to 5W.
Kit & Assembly Requirements
At this time, this modification is available only as a kit.
Assembly requires soldering several small SMD components, including:
- 0805
- 1206
- SOT-23-3
- One pad of a 0603 capacitor C512
- A direct connection to a pin on the STM32
The STM32 pins are extremely small, making this installation significantly more challenging than the soldering required to assemble the QMX itself. This kit is not recommended for beginners. You should be comfortable with fine-pitch SMD soldering and working with small components before attempting this modification.
Soldering to the STM32 may not be needed as the PTT_P pin can be used as a substitute. Please note that this would prevent the operation of an external amplifier that requires the use of this pin (the QMX PA 50W for example). In addition, this obviously can only be used by one mod. If you already use or plan to use my other mods that would normally require the use of the unused LPF pins on the STM32, you would not be able to without performing the more difficult soldering for those mods. In your band config you would then enable PTT Positive on BOTH transmit and receive. This will need to be done on each band that you plan to use an external LPF.
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.
Add one, two, or even three additional bands to your QMX with this mod. Check out my LPF Bypass Mod to open up your QMX from 2200m to 6m when using an appropriate external LPF (and BPF mod).
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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