BNC Connector Guide: Test Equipment, Security Cameras, and Two-Way Radios

The BNC connector was introduced in the late 1940s and it's still on virtually every oscilloscope, spectrum analyzer, signal generator, and commercial two-way radio sold today. Its quarter-turn bayonet locking mechanism is fast, reliable, and nearly impossible to accidentally connect incorrectly. Understanding what's connected to your BNC port — and what impedance it expects — is essential before ordering cables for test bench, CCTV, or radio applications.

What BNC Is

BNC stands for Bayonet Neill-Concelman, named after engineers Paul Neill and Carl Concelman. The bayonet coupling uses two pins on the male connector that engage L-shaped slots on the female connector body, locking with a quarter turn. The body is approximately 14mm in diameter. BNC is rated from DC to 4 GHz (beyond that, connector geometry starts to cause reflections). It's rated for 500V RMS isolation and typically handles 80W of RF power at low frequencies.

The connector's age and ubiquity mean you'll find it in almost every RF-adjacent domain: laboratory equipment, broadcast video, CCTV, military and commercial portable radios, amateur radio handhelds, and older networking equipment. The same quarter-turn mechanism that made BNC the first-choice connector in 1949 is still why technicians prefer it on equipment that gets connected and disconnected frequently.

50-Ohm vs 75-Ohm BNC: Physically Identical, Electrically Different

This is the most important thing to know about BNC: both 50-ohm and 75-ohm versions exist, and they are physically identical. A 75-ohm BNC cable will mate perfectly with a 50-ohm BNC port. The connectors will lock, the center pin will contact — but the impedance mismatch will cause a reflection coefficient of about 0.2, which represents roughly 4% of power reflected. This is measurable but minor in most applications.

The practical risk is buying cheap 75-ohm BNC cables from a camera supply store and using them in a 50-ohm test bench setup. For oscilloscope work and audio frequency signals, the mismatch usually doesn't matter. For calibrated RF measurements, it introduces error. Always check the impedance marking on the device and on the cable before assuming they match. Most test equipment and radio equipment uses 50-ohm BNC. CCTV cameras and video distribution equipment use 75-ohm BNC.

Equipment That Uses 50-Ohm BNC

Oscilloscopes (Tektronix, Keysight, Rigol, Siglent) use BNC on all input channels. Spectrum analyzers have BNC inputs on older and smaller instruments. Signal generators and function generators use BNC for their output. Vector network analyzers (VNAs) at the lower price point (NanoVNA, NanoVNA-H4) use SMA, but many bench-grade VNAs use BNC or N-type. SDR receivers in older designs sometimes use BNC.

Commercial two-way radios from Motorola's classic lines — the HT750, HT1250, GP300, and GP380 — use BNC antenna connectors. Kenwood TK-series commercial handhelds also use BNC. Military handheld equipment has historically used BNC extensively. Some amateur radio handhelds, particularly older Icom and Yaesu HTs, use BNC.

Equipment That Uses 75-Ohm BNC

Analog CCTV cameras almost universally use 75-ohm BNC for video output. DVR and NVR inputs are 75-ohm BNC. Video distribution amplifiers, video switchers, and broadcast video patchbays all use 75-ohm BNC. If you're working with security camera systems or broadcast video infrastructure, all your BNC cables should be 75-ohm.

BNC to N-Type: Test Bench to Antenna

Connecting BNC test equipment to an N-type antenna or N-type feedline is one of the most common bench cable needs. This comes up constantly when characterizing antennas with a spectrum analyzer or VNA that has BNC inputs, or when testing a signal through an N-type feedline on a BNC-equipped signal generator. Cable choices matter here: RG400 and RG142 use PTFE dielectric, which provides better phase stability across temperature and humidity than RG58's polyethylene dielectric — important for calibrated measurements.

RG58 BNC to N-Male  |  RG400 BNC to N-Male  |  RG142 BNC to N-Male

BNC to SMA: Instruments to Modern RF Devices

SDR dongles, GPS modules, and newer compact instruments use SMA. When your oscilloscope or signal generator has a BNC port and your target device has SMA, you need a BNC-to-SMA cable. RG58 is adequate for most general-purpose bench connections.

RG58 BNC Male to SMA-Female

BNC to TNC: Military and Tactical Use

TNC is essentially a threaded version of BNC — same diameter, same internal geometry, but with threads instead of bayonet locking. Military and aviation equipment often specifies TNC over BNC precisely because the threaded connection resists vibration and cannot be inadvertently bumped loose. BNC-to-TNC cables are common in military depot maintenance environments where BNC test equipment interfaces with TNC-equipped field radios.

RG58 BNC to TNC  |  RG142 BNC to TNC

BNC to PL-259: Test Equipment to Ham Radio Feedlines

When using a BNC-equipped VNA or antenna analyzer to check the SWR of a ham radio feedline (which terminates in PL-259), you need a BNC-to-PL-259 adapter cable. RG400 is the better choice here for its PTFE dielectric stability, which reduces phase error during SWR measurements.

RG400 BNC Male to PL-259

BNC-to-BNC: Bench Jumpers and Test Loops

BNC-to-BNC jumpers are used on test benches to connect instruments together, create through-cable paths for calibration, and provide loopback connections for testing. RG400 is preferred for test bench BNC-to-BNC jumpers due to its PTFE dielectric and double-braid construction — it holds calibration better than RG58 across temperature changes in a lab environment.

RG400 BNC Male to BNC Male

Cable Choice for BNC Applications

RG58: General-purpose, polyethylene dielectric, adequate for most bench and field use. Use for general BNC connections where phase stability is not critical.

RG400: Military-specification double-braid coax with PTFE dielectric. Better phase stability with temperature, higher power handling, more mechanically durable. Use for test and measurement where calibration accuracy matters, or any application that sees heat cycling (vehicle engine bays, outdoor equipment).

RG142: Single-braid PTFE coax. Between RG58 and RG400 in cost. Common in military and aerospace applications. Use for precision lab work where RG400's double braid would be over-specified.

Quick Visual Identification

BNC connectors are easy to identify: round body approximately 14mm in diameter, two small pins protruding from the shell of the male connector that engage L-shaped slots in the female. The bayonet lock requires a quarter turn to engage and disengage. The body is usually nickel-plated or silver-plated. No threads visible on the outside (that would be TNC). No visible solder cup or sleeve (that would be PL-259).