13 Feb Testing Coax Cable Networks with the Coax Clarifier
The Coax Clarifier sports many functions useful for working with cable network systems. In addition to its other capabilities like cable length measurement, testing coax cable, tone tracing, and identifying cable end-points through splitters, the Clarifier includes Quality Mode and Return Loss testing. Quality Mode measures and displays a dB reading of coax cable network quality through splitters and connecters to multiple end-points. As long as the system is unpowered and properly terminated during testing, a fully installed network can be measured directly from the line input or building demarc.
The Coax Clarifier tests quality by injecting a radio frequency (RF) signal into the cable network and computing the return loss (RL) from observed signal degradation. The RL number indicates cable network quality and therefore displays the network’s ability to carry a signal.
Return Loss is a measure of the signal reflection voltage standing wave ratio (VSWR) expressed in decibels (dB). RL ranges from 0 dB for a cable with a dead short to infinity for a theoretically perfect cable with absolutely no loss. Realistically, the Coax Clarifier reports the RL as a number between 0 and 40 dB with 40 dB being the highest quality observable.
One can picture how return loss affects a cable signal by imagining a classic carnival game: The Water Racer. In that game, water is shot out of a nozzle toward a small target. The goal is to get as much water as possible into the target to make the racecar speed along to the finish line. Hitting the sides of the target causes the water stream to splash off and water goes everywhere except the target, causing the racecar to slow down. The water not reaching the target is ineffective, aka loss, aka Return Loss.
RF cable networks are subject to the same limitations. In a well matched network, most of the signal applied to the cable reaches its target. That target being the TV receiver, cable modem, radio transmitter, etc. When obstructions are present along the cable path, in the form of improperly matched cables, connectors, or shorts and opens, the signal is reduced due to loss, aka Return Loss.
In a perfect water race the RL value will be high number which indicates most of the water hit its target. In a perfect cable installation, the RL number will be high as well, indicating most of the signal reached its destination.
Measuring cable quality and observing return loss is a fast, accurate way of representing how well a cable network will carry its intended signal. The Coax Clarifier displays this number within seconds of being attached to a cable making testing and troubleshooting racecar fast.