## Common ground
All options describe passive RF devices that split or combine signals with a 90-degree phase difference, commonly used in communication and signal processing systems.
## Options at a glance
**8517.79 – Data/network use**
- **Defining trait:** Designed specifically for data communication or networking equipment.
- **Typical examples:** Couplers in Ethernet switches, wireless routers, or fiber-optic transceivers.
- **Best fit when:** The device is integrated into a networked system where signal routing and data integrity are key.
**8534.00 – PCB form factor**
- **Defining trait:** Built as part of a printed circuit board (PCB), not a standalone module.
- **Typical examples:** Embedded couplers on a motherboard or RF PCB assembly.
- **Best fit when:** The device is permanently mounted on a circuit board and not intended for separate installation.
**8543.70 – 90° RF coupler with SMA ports**
- **Defining trait:** A discrete, metal-housed, four-port passive RF component with SMA connectors, specifically for phase-splitting in microwave/radar systems.
- **Typical examples:** Radar signal combiners, antenna feed networks, test equipment.
- **Best fit when:** The product is a standalone, ruggedized RF module used in high-frequency or high-power applications.
## Key differences
| Feature | 8517.79 (Data use) | 8534.00 (PCB form) | 8543.70 (SMA metal housing) |
|---------------------|--------------------|--------------------|-------------------------------|
| Form factor | General module | Integrated on PCB | Standalone, discrete |
| Connector type | Not specified | Not specified | Female SMA ports |
| Primary application | Data networks | Embedded electronics | RF/microwave systems |
## How to choose
- Is it used in data communication or networking gear? → 8517.79
- Is it built directly into a circuit board (not removable)? → 8534.00
- Does it have four SMA ports on a metal case and handle RF/microwave signals? → 8543.70
## Overlaps & pitfalls
A device could fit multiple categories: e.g., an SMA-based coupler embedded in a PCB might qualify under both 8534.00 and 8543.70. If the product is used in a networked system, it may also match 8517.79.
**Priority rule:** Use the **main function or physical form** as the deciding factor. If it’s a standalone RF module with SMA connectors for radar/antenna use, choose 8543.70. If embedded in a PCB, choose 8534.00. If used in data systems, prioritize 8517.79