BNC Cable Buyer’s Guide: Choosing Between 50 Ohm and 75 Ohm

When sourcing a BNC cable for your laboratory, manufacturing floor, or broadcast studio, it is easy to assume that “a cable is just a cable.” Because the Bayonet Neill–Concelman (BNC) twist-and-lock connector looks physically similar across different applications, procurement teams often buy whatever is cheapest or readily available.

This is a critical mistake. BNC cables are manufactured with specific coaxial wires designed for completely different industries. Buying the wrong impedance will cause severe signal loss, data corruption, or video ghosting. This guide will help you procure the exact BNC cable your engineering team actually needs.

Quick Comparison Table: 50 Ohm vs. 75 Ohm

Specification	50 Ohm BNC Cable	75 Ohm BNC Cable
Common Cable Types	RG-58, RG-174, RG-213	RG-59, RG-6, RG-179
Primary Industry	RF Testing, Telecommunications, Data	Broadcast Video (SDI), CCTV, Audio
Signal Focus	Maximum power transfer	Minimum signal attenuation (loss)
Center Pin (Connector)	Thicker	Noticeably thinner

1. 50 Ohm BNC Cables: The RF and Lab Standard

If your company builds, tests, or deploys Radio Frequency (RF) equipment, you need 50 Ohm BNC cables. This impedance is the internationally agreed-upon compromise between power handling and signal loss.

• Main Applications: Connecting oscilloscopes, signal generators, network analyzers, and amateur radio transceivers.
• Buyer’s Tip: When purchasing 50 Ohm BNC cables (like RG-58), pay attention to the cable’s dielectric material. Higher-quality dielectrics ensure a more stable Velocity Factor, meaning the RF signals travel through the cable at a highly predictable speed—a crucial metric for precise phase measurements in the lab.

2. 75 Ohm BNC Cables: The Video and Broadcast Standard

If your application involves transmitting video or audio signals over long distances, you need 75 Ohm BNC cables. At 75 Ohms, a coaxial cable exhibits the lowest possible signal attenuation, making it ideal for preserving weak analog or digital video streams.

• Main Applications: HD-SDI/4K video routing in broadcast studios, closed-circuit television (CCTV) security systems, and digital audio (S/PDIF).
• Buyer’s Tip: Look for RG-6 or RG-59 cables. For modern 4K or 8K SDI video, ensure the BNC cable is explicitly rated for “12G-SDI” to guarantee it can handle the massive bandwidth without dropping frames.

3. What Happens If You Mix Them?

Never use a 75 Ohm BNC cable to connect two 50 Ohm RF instruments, or vice versa.

While a 50 Ohm connector and a 75 Ohm connector can sometimes physically mate, the impedance mismatch creates a reflective barrier. A portion of your signal will bounce back to the source. In a high-power RF setup, this reflection can overheat and destroy the transmitter. In a video setup, this mismatch causes “ghosting” (faint double images) or complete loss of the digital sync signal.

Procurement Checklist

Before clicking “buy,” verify these three parameters with your engineering team:

1. Impedance: 50 Ohm (for RF/Data) or 75 Ohm (for Video)?
2. Cable Jacket: Do you need PVC (standard indoor), Plenum-rated (for running through air ducts/ceilings), or PE/Polyethylene (for outdoor/UV exposure)?
3. Shielding: For environments with high electromagnetic interference—or when connecting sensitive low noise amplifiers (LNAs)—specify “double-shielded” or “100% foil + braid shield” BNC cables to prevent external noise from corrupting your signal.

Conclusion

A BNC cable is a precision transmission line. By strictly separating your 50 Ohm RF cables from your 75 Ohm video cables and selecting the appropriate shielding and jacket materials, you will eliminate the most common source of system errors and ensure your equipment operates at peak performance.

Frequently Asked Questions (FAQ)

Q1: How can I tell if an existing BNC cable is 50 Ohm or 75 Ohm?

The easiest way is to read the text printed on the cable jacket. Look for “RG-58” (which means 50 Ohm) or “RG-59” / “RG-6” (which means 75 Ohm). Alternatively, inspect the BNC connector itself; 50 Ohm connectors have a white plastic ring (dielectric) around the center pin, while 75 Ohm connectors often have an air gap.

Q2: Are BNC cables better than RCA cables?

Yes, significantly better. BNC cables feature a locking bayonet mechanism that prevents accidental disconnection. Furthermore, BNC cables are true coaxial cables with strictly controlled impedance, providing far superior shielding against interference compared to consumer RCA cables.

Q3: Can I use a BNC adapter on the end of a BNC cable?

Yes, BNC adapters are frequently used on the ends of BNC cables to convert the interface to SMA, N-Type, or RCA. However, you must ensure that the adapter matches the impedance of the cable (e.g., only use a 50 Ohm BNC-to-SMA adapter on a 50 Ohm BNC cable).