Only Connect: Ten things to consider when choosing a coax connector

Welcome to another post in the series by Nick Locke, of Nicab Ltd, who has over 15 years experience in the electronics manufacturing industry specialising in interconnection cable assembly.
In my previous Blog “Coaxial Connector Guide” I gave you a comprehensive guide to common connector types.  I have been asked since to give a bit more information about the type of information you need to help choose the connector that is right for your application.

Here is my top 10 things to consider when choosing the coax connector.

1. Frequency of Operation
Frequency refers to the number of times a periodic action occurs in one second. The SI unit for measuring frequency is hertz. RF connectors are grouped into families, or series. Each series is designed to operate in a frequency range. SMA connectors are an ideal connector for many applications due to its wide frequency range of 0-18 GHz.

2. Characteristic Impedance
Impedance matching is a crucial consideration in the designing process. The SI unit for measuring impedance is Ohms. Most connectors operate between 50-95 ohms. RF connectors used in audio and video applications, such as BNC and F connectors usually operate at 75 ohms. Most 2400 MHz applications operate at 50 ohms.

3. Insertion Loss
Insertion loss, expressed as a ratio in dB relative to the transmitted signal power, refers to the amount of signal power lost in transmission due to device interference. Insertion loss is commonly referred to as attenuation. The farther the signal must travel, the higher the attenuation. Many factors affect insertion loss including coax cable type and length. The ultimate goal of any RF connector is to minimize attenuation.

coax-formula.jpgIf the power transmitted by the source is PT and the power received by the load is PR, then the insertion loss in dB is given by:

4. Power Handling
Most RF connectors used in the telecommunications industry safely operate up to 500 volts. Usually the larger the connector, the higher the power handling. For instance, N Type connectors can handle up to 2,700 volts.

5. Gender
In the world of RF connectors, plugs are typically referred to as "male" and are threaded on the inside. Jacks are usually "female" and contain threads on the outside. Not all RF connectors are threaded. MCX connectors utilize a snap on mating mechanism. A good rule of thumb is that plugs house the contact pin.   Except for Reverse Polarity Connectors that have a Mae body and female centre contact, most commonly used in wireless network systems.

6. Form Factor
Since the development of the first UHF connector in the 1930's, Coax connectors have been getting smaller. The micro-miniature IPX connector boasts a profile of only 2.5mm! Keep in mind however; there is a trade-off between size and power handling.

7. Durability
Many factors influence the ruggedness of an RF connector. How often will the connector be connected and disconnected? Most RF connectors are rated up to 500 mating cycles. Is the connector for outdoor or indoor use? At what temperatures will the connector be subjected to?

8. Environmental Considerations
The main factors to keep in mind concerning durability involve environmental considerations. Mil-Spec RF connectors undergo testing standards which simulate environmental conditions such as vibration and corrosion. These standards are usually expressed in MIL-STD-XXX format.

9. Coupling Style
The mating mechanism associated with an RF Connector is another one of the factors concerning durability. The common threaded interface provides a secure connection for SMA connectors, but is not convenient for frequent disconnects as the bayonet locking feature of the BNC connector. Snap on mating is becoming more common in more space critical applications.  

10. Cost
Most often, despite finding the perfect Coax connector for your RF application, the final decision comes down to budget. SMC and SMB connectors are on the higher end of the price spectrum , while F and BNC connectors remain on the lower end.

These considerations serve as a reference summary of top considerations when choosing a coax connector for your application. Trade off's often occur between these factors. However, each project demands its own set of requirements. Decide what works best for YOUR project.

Or talk to your friendly cable assembler who will be happy to help!

Previous Only Connect entries:

* Only Connect: How to promote UK Manufacturing #4

* Only Connect: Renewable energy made in the UK (Going Green #5)

* Only Connect: Electronics and natural disasters

* Only Connect: A simple guide to DVI Connectors

* Only Connect: A Thunderbolt of innovation

* Only Connect: The golden principle of good design

* Only Connect: Common fiber connectors - a guide

* Only Connect: Product innovation - mixing signal

* Only Connect: IPC versus Greenpeace electronics scorecard

* Only Connect: Product innovation from Space

* Only Connect: Apple's MagSafe connector makes sense

* Only Connect: Coaxial connections guide

* Only Connect: Eco-gift for Christmas (Going Green #4)

* Only Connect: How to promote UK Manufacturing #3

* Only Connect: On using Ethernet connectors

* Only Connect: High-temp superconductors good news for renewable energy

* Only Connect: A positive mindset for winning government contracts

* Only Connect: A Top Ten of connector manufacturers

* Only Connect: Red toxic sludge points the way (Going Green #3)

* Only Connect: Handy Design Tips #4 - Explosion proof Ethernet

* Only Connect: We're changing the world into a better place, baby!

* Only Connect: Handy Design Tips #3 - The right wrong connector

* Only Connect: Proud of the Made In UK mark

* Only Connect: Handy Design Tips #1 - Colour

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