By Sanjay Chawla On Nov. 20, 2008 Site: Electronics Design Engineering Lounge (Public) Type: Blog - Tags: Electronics - # of views: 10741

I have observed that people do few common mistakes using the BNC connectors and result in damaging them but with little care taken these are easy and convenient to use. These types of connectors cost approximately $2 per piece. I wanted to suggest here some information on BNC connectors which if people clutch, then be able to avoid the common mistakes of usage and avoiding damage.

BNC connector

The BNC (Bayonet Neill Concelman) connector is a very common type of RF connector. They are used for terminating coaxial cable for RF signal connections and can be used in a wide number of applications - from any form of RF equipment including radio communications equipment to test equipment including everything from oscilloscopes to audio generators, and power meters to function generators. In fact BNC connectors are used in applications where coaxial or screened cable is required.

The BNC connector has many attributes. One is that it has a bayonet fixing. This is particularly useful because it prevents accidental disconnection if the cable is pulled slightly or repeatedly moved. Another advantage is that it is what is termed a constant impedance connector. This is particularly important for RF applications and means that the connector presents the same impedance throughout its length

These exist in 50 and 75 ohm versions. Originally all were 50 ohm and were used with cables of other impedances, the small mismatch being negligible at lower frequencies. The 75 ohm types can be recognized by the reduced or absent dielectric in the mating ends.

There are two main variants of the BNC connector assembly method:

• Compression gland type
• Crimp type

Avoiding Common Mistakes

- BNC plugs are designed not only for the required impedance, but also to accept a particular coax cable format. In this way all the internal piece parts are compatible with the coaxial cable used. It is therefore necessary to specify the BNC plug for use the cable to be used. Although there is some latitude, it is naturally best to select the correct cable format.

- Unfortunately right-angled connectors have a marginally higher level of loss than their straight through counterparts. This may not be significant for most applications, but at frequencies near the operational limit of the connector there may be a small difference.

- There is a very real physical difference between 50-ohm and 75-ohm type N connectors. The 50-ohm male pins are bigger than the 75-ohm pins and will damage a 75-ohm female connector. Likewise if a 75-ohm male is mated with a 50-ohm female there will not be good electrical contact.

- Do not cut the cable at an angle instead cut it smoothly in perpendicular direction.

- Be careful not to cut through the cable braid

- For Quad shield cable, pull back the outer layer of braid, remove the outer layer of foil, and then pull back the inner layer of braid. Leave the inner layer of foil around the dielectric.