What is the difference between 50 ohm and 75 ohm coaxial cable and when do I use each?
50 vs 75 Ohm Coaxial Cable
The 50 ohm and 75 ohm standards are deeply embedded in the RF industry, with different connector ecosystems, test equipment, and design practices for each.
| Parameter | Semi-Rigid | Conformable | Flexible |
|---|---|---|---|
| Loss (dB/m at 10 GHz) | 0.8-2.5 | 1.0-3.0 | 1.5-5.0 |
| Phase Stability | Excellent | Good | Fair |
| Bend Radius | Fixed after forming | Hand-formable | Continuous flex OK |
| Shielding (dB) | >120 | >90 | >60-90 |
| Cost (relative) | 2-5x | 1.5-3x | 1x |
- Performance verification: confirm specifications against the application requirements before finalizing the design
- Environmental factors: temperature range, humidity, and vibration affect long-term reliability and parameter drift
- Cost vs. performance: evaluate whether the application demands premium components or standard commercial grades
Frequently Asked Questions
Can I use 75 ohm cable for a Wi-Fi antenna?
Technically yes, but it introduces a mismatch: the Wi-Fi radio output is 50 ohms, and the antenna is designed for 50 ohms. Using 75 ohm cable creates a 14 dB return loss at both ends. The mismatch loss is 0.18 dB per transition (0.36 dB total). For receive: the 0.36 dB additional loss is usually acceptable. For transmit: the reflected power returns to the PA, which may cause heating or damage at high power levels. Best practice: always use 50 ohm cable and connectors for 50 ohm systems.
Why does the cable TV industry use 75 ohm?
CATV is a receive-only application (from the subscriber perspective): minimum loss is the priority (signals travel long distances through the cable plant). Power handling is not a concern (signal levels are very low, typically -10 to +15 dBmV). The 75 ohm impedance provides 10-15% lower loss per meter than 50 ohm cable, which matters over long cable runs (100-500 ft from the tap to the TV). Additionally: the 75 ohm F-type connector is extremely cheap ($0.10), enabling mass deployment. The CATV industry ships billions of F-connectors per year.
What about 93 ohm and 95 ohm cables?
These are specialty impedances: 93 ohm (RG-62): used in some legacy data networks (ARCnet) and pulse/timing applications. Provides even lower loss than 75 ohm but with less power handling. 95 ohm: used in some military timing distribution systems. These impedances are rare in modern RF design. The industry has standardized on 50 ohm and 75 ohm with very few exceptions.