Junky Talk

Coaxial Cable

So, I thought I should just should just share a bit of information in regard to cabling when it comes to our wireless audio systems.

When setting up our wireless systems and get ready for our shows we use terms such as BNC connectors SMA connector or N-type connectors. These are the common types of connectors when working with wireless audio. What is the type of cable we use? That’s right, it’s called coaxial cable. When it comes to coaxial cable we have what we call “resistance of the cable”, measured in Ohms, which will differ depending on the application of the cable.

Now, in the previous paragraph I mentioned “resistance” of a cable. What is resistance? Well before we get there let me get this out of the way since we are dealing with wireless(RF) systems here. This is basically how an RF system works…. when speaking into a microphone there are flows of electrical current in the microphone which are then converted at the antenna stage to electromagnetic waves. What? Okay, as the electrical current moves through the system/cabling, a magnetic charge is created, now when the electrical charge and magnetic charge combine they create an electromagnetic wave, this type of wave is able to move through air, and this is how information moves from a transmitter to a receiver. Through air, by electromagnetic waves.

Now why are we involving cables and resistance here? When engineers working with coaxial cable in the 1900s took measurements, it was discovered that depending on your application, for effective power and signal flow through the cable, your cable needed to have a certain amount of resistance to it. Do we pour resistance onto a cable from a bucket? No, the characteristics, or the design of the cable determines how much resistance a cable would have against the flow of power and audio information. It’s like running through wind, if it’s heavy wind you will get to your destination but you will need to run harder, meaning, using more energy against the wind to reach your destination.

So, let’s go through how coaxial cable is made. Refer Fig.1

• Conductor: This is the core of the cable and is how information flows from direction A to B

• Dielectric: The dielectric, which is usually plastic, or foam or a mixture of the two, is a buffer created between the copper core and the shield. This also is designed to keep the conductor straight.

• Shield: This is usually made of aluminum, copper and/or foil. It is meant to protect the center conductor against the environment’s contamination.

• Jacket: This is made out of PVC and serves pretty made a similar if not the same purpose as the shield

Fig. 1

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Now that we know what’s what….

Depending on characteristics of material used, in the construction of the coaxial cable, your results will differ. Also, according to your application.

The amount of resistance that applies to us in the audio world, is 50 Ohms. This is why… the engineers, after testing, saw that you could pass decent amounts of power through a coaxial cable if you have a certain resistance (30 Ohms), but power is not the only important factor here, we also consider the amount of information lost over a certain distance. Certain information needs a certain amount of power in order for effective transmission, this is how we have 10mW, 50mW, 100mW or 250mW power output on our equipment.
We also need a different resistance so that we do not lose too much signal integrity along the way, and this is 77 Ohms.

What now? We need enough power to get the information somewhere, but we also need to not lose our signal integrity along the way. We need to be diplomatic here…we need middle ground. Our engineers, the people that dedicate their lives to all this needed to make a decision. Whatever needs more energy or power to be effectively transmitted will need to use 50 Ohm and whatever doesn’t require a much power will use 75 Ohm coaxial cable.

Now, what’s a cable without its connector… your resistance needs to be the same between your system, connector and cable.

Your wireless partner: RF Junky

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