Understanding BNC Connector Fundamentals
Wiring a BNC connector correctly is a fundamental skill for anyone working with radio frequency (RF) and video equipment, from CCTV installations to amateur radio setups. The Bayonet Neill–Concelman connector, named after its bayonet mounting mechanism and its inventors, Paul Neill and Carl Concelman, is designed for quick connect and disconnect while maintaining a stable 50 or 75-ohm impedance, which is critical for signal integrity. The most common types are the crimp, compression, and twist-on versions, each with its own advantages. Crimp connectors offer the most reliable and durable connection for permanent installations, while twist-on types are better for temporary fixes. Using the wrong type or a poor installation technique can lead to signal loss, reflected power (measured as Voltage Standing Wave Ratio or VSWR), and ultimately, system failure. For instance, a VSWR greater than 1.5:1 is often considered unacceptable in professional applications, as it indicates a significant impedance mismatch caused by a faulty connection.
Essential Tools and Materials
Before you begin, gathering the right tools is half the battle. Attempting a BNC installation with improper tools will almost certainly result in a subpar connection. You cannot achieve a professional result with a pair of household pliers. The specific tools required depend on the connector type, but a basic kit for a crimp-style BNC connector should include the following items. Using precision tools ensures the coaxial cable is prepared without damaging the delicate inner conductor or the braided shielding, which carries the ground signal.
| Tool/Material | Purpose | Critical Specification/Note |
|---|---|---|
| Coaxial Cable Stripper | To precisely remove the outer jacket, shield, and dielectric without nicking the center conductor. | Must be calibrated for your specific cable diameter (e.g., RG59 or RG6). A standard knife is not recommended. |
| Coaxial Cable Cutter | To make a clean, square cut on the cable end. | A sharp, dedicated cutter prevents cable deformation. |
| Crimping Tool | To permanently secure the connector to the cable. | Must have the correct die size for the BNC connector being used (e.g., for .240″ hex crimp). |
| BNC Connector | The connector itself, matched to the cable type. | Ensure it’s for the correct cable (e.g., RG59 75-ohm) and connector type (crimp/compression). |
| RG59 or RG6 Coaxial Cable | The cable being terminated. | RG59 is common for shorter-run video; RG6 has lower loss for longer runs or higher frequencies. |
Step-by-Step Wiring Procedure for a Crimp-Style BNC
This guide focuses on the crimp-style BNC connector for RG59 cable, a common scenario for CCTV systems. Follow these steps meticulously. The key is precision and avoiding any damage to the components.
Step 1: Prepare the Cable
Start by using the coaxial cable cutter to make a perfectly straight cut about 1/2 inch (12-13 mm) from the end of the cable. Any angle on the cut will make the subsequent steps difficult and can compromise the connection. A clean, square cut is non-negotiable.
Step 2: Strip the Outer Jacket
Select the appropriate setting on your coaxial stripper for RG59 cable. The goal is to remove the outer black PVC jacket to expose the braided copper shield beneath. A typical stripping depth is about 3/8 inch (9-10 mm). Insert the cable into the tool, rotate it a few times, and remove the jacket. Be careful not to cut into the braid. You should see a silvery braid surrounding a white dielectric foam.
Step 3: Prepare the Braid and Dielectric
This is the most delicate part. Gently fold the braided shield back over the remaining outer jacket. This creates a conductive surface for the outer part of the connector to grip. Next, use the stripper’s second blade to score and remove about 1/4 inch (6 mm) of the white dielectric foam, exposing the solid copper center conductor. Be extremely careful not to nick or scratch this conductor. Even a small nick can create a point of high impedance.
Step 4: Assemble the Connector Components
A crimp BNC connector typically consists of three parts: the main body, a ferrule, and a pin contact. Slide the ferrule onto the cable first, with the wider end facing the cable end. Then, carefully insert the center conductor into the hollow pin contact until it stops. The pin should have a small hole or slot; the center conductor should be visible through it. Using the crimping tool’s specific die for the pin, crimp the pin onto the center conductor. This creates the central electrical connection.
Step 5: Final Assembly and Crimping
Push the main body of the BNC connector onto the prepared cable end. The folded-back braid should slide between the connector body and the dielectric. The pin, now attached to the center conductor, will click into place inside the connector body. Ensure everything is seated fully. Finally, slide the ferrule up into the connector body and use the larger die on your crimping tool to crimp the ferrule, securing the entire assembly to the cable’s outer braid and jacket. This provides the mechanical strength and the ground connection. A proper bnc wiring diagram can be invaluable for visualizing this final assembly stage, especially when dealing with hybrid cables or more complex pinouts.
Testing and Troubleshooting Your Connection
Once the connector is installed, your job isn’t finished. You must test it. A visual inspection is the first step: check that the center conductor is not too long or too short and that the braid is neatly folded back without any stray wires that could cause a short circuit. The best tool for testing is a cable tester or an ohmmeter. With the connector disconnected, use the ohmmeter to check for a short between the center pin and the outer barrel; there should be infinite resistance (no continuity). Then, check the continuity of the center conductor from one end of the cable to the other; the resistance should be very low, typically less than 1 ohm for a short cable. For RF applications, using a VSWR meter is the ultimate test. A well-made connection on a good cable will show a VSWR very close to 1:1. If your signal is noisy or non-existent, re-check your crimps and the cable preparation steps—most faults occur there.
Choosing the Right Cable and Connector for Your Application
Not all BNC applications are the same. The choice between cable types like RG58, RG59, and RG6 has significant implications. RG58 (50-ohm) is often used in radio communications, while RG59 and RG6 (75-ohm) are standards for video. The key difference is signal attenuation, measured in decibels per 100 feet (dB/100ft). For example, at 400 MHz, RG59 might have an attenuation of 6.5 dB/100ft, while higher-quality RG6 might only have 4.5 dB/100ft. This means over a 100-foot run, you lose significantly less signal with RG6. Similarly, for harsh environments, you might need a connector with a rubber boot for strain relief or a weatherproof seal. Always match the connector’s impedance (75-ohm for video) to the cable’s impedance to prevent signal reflections. Using a 50-ohm connector on a 75-ohm cable will degrade performance, especially over longer distances or at higher frequencies.