making the right connection...
The humble connector plays a very important role in the communications chain. It can make or break your system - and often does.

When faced with the vast array of connectors available, choosing the correct type for the job can be confusing. Each type is designed for a specific use for different cable types and characteristic impedance. In order to avoid signal or power loss, the connector must be compatible with the wire size, able to handle the required power, be designed for the frequency being used and suit the environment it is to be put in. It is important to ensure that the VSWR and voltage rating quoted are suitable.

RF connectors differ from audio types, where a different material insulates the centre or active pin from the earth shield causing radio frequencies often to be bypassed to earth. As a general rule, threaded types are most reliable in high frequency applications and in non permanent installations the bayonet type is often the easiest solution. Weatherproofing is essential in marine applications.

Connector quality is important and little is saved by opting for inferior cheaper types, leading to electrical noise and intermittent connection.

Shells of half-hard brass, nickel or silver plated (nickel) are superior to die-cast zinc alloy, which is used in some low frequency data transmission connectors. If the surface of the shell is marred by any roughness or burrs, coupling or decoupling can become difficult and losses can occur. Generally PTFE (polytetrafluoroethylene or teflon) is the preferred material for the dielectric.

Five types of connector stand out as being most commonly used. These are the standard Belling-Lee, and the BNC, UHF/PL259, N and TNC types.

1. The most common type of connector, commonly known as the Belling-Lee or RF, Coaxial or TV connector, features a push fit type coupling and is best suited to TV/VCR applications.
   
   
2. The BNC connector can be used for all coaxial connections from audio to UHF. It features a more robust bayonet type coupling for quick removable connection and is often used with many test instruments.
   
   
3. The UHF or PL259/SO239 connector is suitable for VHF and lower frequency applications. It is often used for frequencies below 200 MHz.
   
   
4. The N Type connector, although harder to assemble than UHF, features constant impedance at cable joints and is well suited to frequencies above 200 MHz.
   
   
5. Where extreme vibration is a factor, as in military and aerospace applications, the TNC connector, similar to the BNC type but threaded, is ideal.
   
   
   

Assembling connectors is not always a simple process. There are so many different types and makes and not all come with the necessary instructions to help you get it right. It would be nice to have one or two simple recipes to suit most types, but life is about variety and variation.

However, quite often, when a connection doesn't work, the reason can be traced to something annoyingly simple. From our experience, we have found that taking the following factors into account should go some way to help you to make the right connection.

• All cuts should be sharp and square.
  Take care not to nick (cut) braid, dielectric or centre conductor. Nicking the braid will reduce the surface area for earthing. Nicking the dielectric may create gaps for the braid to come into contact with the inner conductor and short out the connection. Nicking the centre conductor can cause strands to fall off reducing the surface area, or if solid, fracture of the whole conductor.
  
  
• Remember to tin the inner conductor first. This makes the solder take quickly, gives a good connection and also binds the strands together on multi-strand conductors, removing the risk of one of these strands shorting to the outer braid when fitting coax to the connector.
  
  
• Do not use excessive heat when tinning and soldering. Overheating can melt the dielectric. As a result the pin becomes loose and you have a poor connection.
  
  
• Make sure no strands of braid come into contact with the inner conductor. Single strands can be difficult to see unless you inspect carefully. It only takes one strand to short out the connection and your antenna won't work. So, it's well worth taking the trouble. NB with grounded antennas it's hard to check for this problem.
  
  
• If you find you have pulled too much braid back, trim the braid off level with the top of the conductor so it doesn't show. It has been known for bits of copper to break off and fall into the job you are doing, which can be quite inconvenient, to say the least.