As far as cable goes, coaxial cable is more susceptible to damage than most. That doesn’t stop many audio pros from whipping it around like any old trampled extension cord. Unlike power cords and CAT5, coaxial cable needs to be handled carefully in order to last, and kept out of certain situations.
One of RF Venue's employees, Nick, prepares to attach a connector to our RG8X type coax
by snipping away some of the braided shield.
Coaxial cable carries high frequency signals through a center conductor in between a thin tube of braided or solid metals called a shield. Insulation in between the center conductor and shield keeps the two conductors from touching one another. An additional (usually black plastic) jacket is placed around the entire assembly. The shielding stops extraneous RF noise from interfering with the signal inside the cable, but can also be used for other purposes like an electrical ground, remote power, or to send additional signals. Since the shape and condition of both shield and conductor are important, small defects can cause a dramatic reduction in signal quality.
Damage from rough or improper handling and accidents is the most common type of damage. Coax has a wide minimum bend radius and the distance between inner conductor and shield should be kept as even as possible along the entire length.
Just because a cable looks OK doesn’t mean it is. Damage is sometimes invisible to the naked eye, which is why we produced this video:
Some of the many possible culprits include:
- One clean hit from a heavy flight case.
- One good stomp from a murderously fashionable high heel.
- Continuous or repetitive stress (creep deformation) from light foot traffic over carpet, etc. Always use drop-over cable covers.
- Crimping due to aformentioned minimum wide bend radius
- Improper coiling. Coax needs to be coiled using the correct technique, which you can watch, here.
- Age. Coax that has been pampered like a baby will still need replacement eventually.
Coaxial cable is not waterproof. Waterlogged cable produces altered electrical characteristics, possibly rendering it useless, or weird. Don’t leave coax out in the rain, even if the connectors are covered since small nicks in the outer sheath can still cause water to enter, and (we really shouldn’t have to tell you this but…) don’t completely submerge cable.
Polyethylene and polyvinyl chloride are used as insulators. These two plastics have relatively low melting points, and can start to soften at temperatures as low as 150 degrees F. If the insulation is exposed to low heat over long periods of time, the position of the center conductor in relation to the shielding may shift as the hot plastics yield. If the center conductor and shielding touch, signal never makes it past that point. Coax should be kept away from heatsinks, stage lights, and other sources of heat. We have even heard of tightly bent cable shorting after being left out in hot sun.
The connector on either end can go bad, whether it is BNC, N, or some other type. Sometimes the damage will be obvious, like a missing center pin. Sometimes it will be hard to see, like if the solder has come loose loose behind the connector, or the termination was improperly performed in the first place. Boning up on how to terminate cables is a great way to solve connector problems. Also, severely oxidized (tarnished) silver plated connectors will attenuate signal and should be cleaned or replaced.
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Leading image courtesy Tkgd2007.