Choose the coaxial cable impedance specified by the connected equipment. Most RF transmitters, antenna systems, wireless devices, and RF test instruments use 50 Ohm coaxial cable, while CATV, satellite television, broadcast video, CCTV, and broadband distribution systems normally use 75 Ohm coaxial cable. The equipment port, cable, connector, adaptor, and termination need to follow the same nominal impedance across the signal path.
Start with the Equipment Impedance
50 Ohm and 75 Ohm describe the characteristic impedance of a coaxial cable, not the DC resistance of its conductor. Characteristic impedance is determined by the cable geometry and dielectric material, so cable diameter or connector appearance cannot confirm the impedance by itself.
The first check is the equipment specification. Confirm the nominal impedance of the source, load, cable, connector, adaptor, and termination before comparing cable loss, flexibility, or installation requirements.
50 Ohm vs 75 Ohm Coaxial Cable at a Glance
The table below summarizes the usual selection path. Individual cable and connector specifications still need to be confirmed for the required frequency, length, power level, and installation environment.
| Comparison Item | 50 Ohm Coaxial Cable | 75 Ohm Coaxial Cable |
|---|---|---|
| Normal system type | RF transmission, wireless communication, antenna links, radio equipment, and RF measurement | CATV, satellite television, broadcast video, CCTV, broadband, and signal distribution |
| Common equipment | Transmitters, receivers, antennas, wireless modules, RF test instruments, and communication equipment | Cable modems, television systems, satellite receivers, video equipment, and broadband distribution devices |
| Common cable families | RG58, RG174, RG316, RG213, and 50 Ohm low loss coaxial cables | RG6, RG11, RG59, and broadcast grade 75 Ohm coaxial cables |
| Common connector interfaces | SMA, N Type, TNC, and 50 Ohm BNC | F Type, IEC, and 75 Ohm BNC |
| Common design focus | RF power transfer, impedance matching, and repeatable RF measurement | Video or broadband signal distribution, impedance matching, and attenuation control |
| Loss review | Compare attenuation at the required frequency and length | Compare attenuation at the required frequency and length |
| Connector check | Confirm that the connector version, cable size, and equipment port are 50 Ohm | Confirm that the connector version, cable size, and equipment port are 75 Ohm |
| Information to confirm | Impedance, frequency, length, insertion loss, power, shielding, connector, and environment | Impedance, frequency, length, attenuation, shielding, connector, and equipment port |
Impedance alone does not show which finished cable assembly has lower attenuation. Cable diameter, conductor construction, dielectric material, shielding, frequency, length, connector transition, and termination quality can all change the final insertion loss.
Choose 50 Ohm or 75 Ohm by Application and Port Type
Choose 50 Ohm for RF Transmission and Measurement Systems
Use 50 Ohm coaxial cable when the transmitter, receiver, antenna, RF module, or test instrument specifies a 50 Ohm interface. This impedance is common in wireless communication, antenna feeder, cellular, GPS, Wi-Fi, radio, and RF measurement systems. The connected cable and connector need to maintain the same impedance as the equipment ports.
RG58, RG174, RG316, RG213, and larger low loss cable families are available in 50 Ohm versions, but their diameter, attenuation, flexibility, temperature range, and power capability differ. A short internal jumper may focus on flexibility and cable diameter. A long antenna feed may require lower attenuation.
Choose 75 Ohm for Video and Broadband Distribution Systems
Use 75 Ohm coaxial cable when the connected equipment is designed for CATV, satellite television, broadband distribution, broadcast video, CCTV, or another 75 Ohm signal path. RG6, RG11, RG59, and broadcast grade 75 Ohm cables are common options, although their attenuation, shielding, jacket, and usable frequency range can differ considerably.
RG6 may suit a building distribution run, while RG11 may be considered when the route is longer and the available installation space can accept a larger cable. RG59 remains common in video and CCTV connections where its size and system specification are suitable. The final cable model still needs to match the equipment port, route length, frequency, and permitted signal loss.
How to Compare Cable Loss
A 75 Ohm design can have lower attenuation than a geometrically similar 50 Ohm design, but this comparison does not apply automatically to different cable sizes and constructions. A larger 50 Ohm low loss cable can have lower attenuation than a smaller 75 Ohm cable at the same frequency.
Compare cable models at the same frequency, length, temperature, and measurement unit. Review the attenuation chart at the highest required operating frequency, then calculate the cable section loss for the finished length. For a completed cable assembly, include connector loss, adaptor loss, and mismatch loss in the insertion loss review.
A cable with suitable bulk attenuation can still produce an unsatisfactory assembly result when the connector transition is poorly matched or the termination process changes the cable geometry. For applications with defined RF performance limits, review insertion loss and return loss data for the finished cable assembly.
What Happens When 50 Ohm and 75 Ohm Components Are Mixed
A coaxial cable is only one part of the signal path. The connector, adaptor, antenna, radio, modem, receiver, transmitter and test equipment should follow the same impedance target wherever possible. When a 50 Ohm system is connected to a 75 Ohm cable, or a 75 Ohm system is connected to a 50 Ohm cable, the signal sees an impedance change at the connection point. That impedance discontinuity reflects part of the signal toward the source instead of delivering it to the load.
At one ideal impedance transition from 50 Ohm to 75 Ohm, the magnitude of the reflection coefficient is 0.2. This corresponds to approximately 4 percent reflected power, a VSWR of about 1.5:1, and a return loss of approximately 14 dB. These figures describe one impedance discontinuity. They do not represent the total loss of every mixed impedance cable assembly.
A complete signal path may contain an impedance change at each cable end, additional connector transitions, adaptors, and frequency dependent phase effects. These discontinuities can combine into insertion loss variation, response ripple, measurement error, reduced delivered power, or poorer return loss. The result needs to be evaluated across the required operating frequency range.
How to Connect a 50 Ohm Device to a 75 Ohm System
When a 50 Ohm device needs to interface with a 75 Ohm system, the matching method depends on frequency range, bandwidth, power level, acceptable insertion loss, and the required measurement accuracy. The solution may use a resistive matching pad, transformer, or another impedance matching network.
An ideal resistive minimum loss pad designed to transform 50 Ohm to 75 Ohm introduces approximately 5.7 dB of insertion loss before cable and connector losses are added. This loss needs to be included in the signal level calculation. A mechanical coaxial adaptor changes the connector interface, but it provides impedance conversion only when its specification includes a defined matching function.
Connector Compatibility in 50 Ohm and 75 Ohm Systems
Connector family and connector impedance need to be checked separately. BNC connectors are available in both 50 Ohm and 75 Ohm versions. Some 50 Ohm and 75 Ohm BNC connectors can physically mate, but that does not make them electrically interchangeable.
SMA connectors are normally used in 50 Ohm RF systems, while F Type connectors are designed for 75 Ohm coaxial applications. Before using a connector in the signal path, confirm its exact part number, nominal impedance, compatible cable, and frequency rating rather than relying on connector appearance alone.
FAQ
Conclusion
Choose 50 Ohm coaxial cable for equipment and signal paths specified as 50 Ohm, and choose 75 Ohm coaxial cable for equipment and signal paths specified as 75 Ohm. After confirming the impedance, compare the operating frequency, finished length, attenuation, power requirement, shielding, routing space, and connector termination. Connector appearance or a mechanical adaptor does not confirm electrical compatibility. If a mixed interface or custom cable assembly is required, confirm the equipment port, cable length, connector requirements, and test limits before finalizing the assembly.