Coax Connector Types: F, BNC, RCA and N Explained

A coax connector does two jobs: it makes the electrical connection and it maintains the cable’s impedance through the joint. A connector that matches neither the cable nor the system undoes the work the cable was chosen to do.

The types are not interchangeable, and the rule that governs them is simpler than the variety suggests.

Quick answer

Connector	Impedance	Typical use	Notes
F	75 ohm	Television, satellite, CCTV, cable TV	Threaded, cheap, needs the right size for the cable’s dielectric
BNC	50 or 75 ohm	HD analog CCTV, SDI, test equipment	Bayonet fit; 50 and 75 ohm versions look alike
RCA (phono)	75 ohm in video and coax digital audio	Consumer video, coaxial S/PDIF	Also used for line-level audio, where impedance practice differs
N	50 ohm	Antennas, outdoor radio runs	Weatherproof, larger, higher power
SMA / MCX	50 ohm, mostly	Small radio and instrumentation links	Not for distribution systems
PL-259 / SO-239	50 ohm	Amateur radio	Often paired with an adapter to a smaller cable

The rule that decides compatibility

A connector has to match three things: the cable’s impedance, its center conductor diameter, and its dielectric diameter and shield type.

The third is where installations fail. F connectors in particular are made in sizes keyed to the dielectric: one for standard RG6, one for quad shield RG6, one for RG59, and one for RG11. Using a standard RG6 connector on a quad shield cable often means the connector cannot slide over the foil and braid layers properly, and the shield ends up folded back or barely making contact.

The result is a joint that passes a continuity test and performs badly. If you are buying connectors for a job, the listing should name both the cable type and the shield type it fits.

F connectors

The F connector is the workhorse of television, satellite and CCTV, and it is a 75 ohm family. It exists in three termination styles, and they are not equivalent.

Style	How it works	Where it belongs
Compression	A ferrule is compressed over the cable’s shield by a tool	Permanent installations. The most reliable of the three
Crimp	A crimp ring is closed over the braid	Permanent installations, with the correct tool and die
Twist-on	The connector is screwed onto the cable	Temporary work and diagnostics only

Compression is the standard for installed work because it makes a consistent mechanical and electrical joint, and because the tool is inexpensive. Twist-on connectors depend on the center conductor making contact by friction, and they degrade with movement.

BNC connectors, and the 50/75 trap

BNC appears in two impedances that are mechanically compatible and internally different. They look the same, mate with each other, and are not interchangeable electrically.

That matters in installations where both worlds meet — a CCTV rack next to radio equipment, or a test bench with a signal generator and a video monitor. Buying by part number rather than by appearance is the only reliable approach, and the impedance mismatch is covered in more detail here.

BNC is also available as a compression and a crimp termination, and in versions designed for specific cable diameters. The same sizing rule applies as for F connectors.

RCA connectors

RCA is a consumer connector used for two different things, which is why it causes confusion.

In video and coaxial digital audio, it carries a 75 ohm signal and is a legitimate coax connector. Cable intended for this has the same impedance discipline as any other 75 ohm run.

In line-level analog audio, the same connector carries a low-level signal on a screened cable where 75 ohm practice does not apply in the same way. A stereo pair of RCA leads is not a pair of 75 ohm transmission lines.

The practical consequence is that an RCA cable sold for video and an RCA cable sold for audio may look identical and be built differently. Where the application is video or digital audio over coax, buy cable specified for it.

N, SMA and the small connectors

These are 50 ohm families from the radio world. The N connector is the weatherproof, larger option for outdoor antenna runs; SMA and MCX are small connectors for instrumentation and short internal links.

None of them belongs in a video distribution system, and none of them accepts the cable used there.

Termination quality is where runs actually fail

The connector is the highest-risk part of a coax run, for three reasons.

The shield connection. The whole point of the shield is that it is continuous and well bonded. A connector that grips the foil poorly, or where the braid is folded back untidily, leaves an impedance discontinuity and a path for interference.

The center conductor. It must be captured reliably. A center conductor that is slightly too short, or that has been scored while stripping, makes a joint that works and then stops working.

Return loss. An imperfect joint reflects part of the signal. On a digital service that shows up as errors; on analog video, as a ghost.

Two habits prevent most of it. Strip the cable with a tool set to the right depth rather than by eye, and pull-test every connector before the cable goes back in the ceiling.

Scenarios

A CCTV installation with RG6 quad shield. Compression F connectors sized for quad shield, one per camera and one per DVR port, all pull-tested.

A satellite dish run. Compression F connectors rated for the cable, with the outdoor joints weatherproofed. Moisture in a connector is a slow, intermittent fault.

A rack with 75 ohm video and 50 ohm radio in the same bay. Separate labeled connector stocks, and cable ends labeled with the impedance. This is the situation where a wrong BNC gets used.

A short patch between a wall plate and a television. A ready-made lead is appropriate, and it should be sold as a 75 ohm video lead rather than an audio lead.

FAQ

Which coax connector is best? The one whose impedance, center conductor size and dielectric size match both the cable and the equipment.

Can I use a twist-on F connector permanently? It will work for a while. Compression is the standard for installed work because it does not depend on friction.

Are all BNC connectors 75 ohm? No. BNC exists in 50 and 75 ohm versions that look identical and mate with each other.

Is an RCA cable a coax cable? For video and coaxial digital audio, yes, and it should be a 75 ohm cable. For line-level audio, the connector is the same but the impedance practice is different.

Do I need a different connector for quad shield RG6? Often yes. Connectors are sized to the cable’s dielectric and shield, and a standard connector may not fit quad shield correctly.

Does the connector affect signal quality? It affects it more than most people expect, because the joint is a discontinuity. A poor connector can spoil an otherwise good run.