What is the Link Margin measurement?
The Link Margin is a measurement that indicates how much MER a a digital channel can lose before it is impossible to “lock” it. This happens when the Link Margin measurement is equal, very close or below zero. Then the decoder error corrector is not able to recover data lost at transmission.
The PROMAX field strength meters show the Link Margin measurement. In many cases users do not care about it. We will learn to appreciate its importance. First you have to understand the concept of error correction.
Measure of the Link Margin in a terrestrial digital television channel
FIRST, WHAT IS THE ERROR CORRECTOR?
The error corrector is the set of stages applied by digital television decoders to recover data. Several algorithms are applied that reverse negative impact of interferences, echoes, etc. Thanks to the error corrector, image and sound of a digital channel are always perfect.
A very simplified block diagram of a digital television receiver in operation
WHAT IF THE ERROR CORRECTOR CAN NOT RECOVER DATA?
When this happens it is because the signal reaching digital decoder does not have enough power or it has degraded excessively. So the user stops watching the television service he was receiving.
A perfect image (left) and an image with artifacts (right) that is very close to be lost because the error corrector is not able to recover information.
WHY IS A HIGH LINK MARGIN IMPORTANT?
Because when an installation ages, expands or is affected by weather, the receiver progressively receives a worse signal that eventually causes, in the language of the user that “sometimes I can’t watch television”.
Link Margin equal to 0 (zero) indicates that if signal loses more MER then channel reception will be impossible. Therefore, although it is technically possible to receive the channel signal whose Link Margin is zero, it is risky to finish an installation or maintenance job in these conditions because at the slightest problem that channel will be impossible to lock.
HOW TO IMPROVE LINK MARGIN?
When deploying a television distribution network, installing an antenna or at any maintenance job, the MER (Modulation Error Rate) of digital channels is usually a very important factor.
But it is also important to pay attention to Link Margin: The higher, the better. That is, when higher value, greater will be signal tolerance against elements that degrade it.
A well-executed television distribution network prevents problems. It's not just for an aesthetic reason! (source)
A proper set amplifier, quality wiring, minimum number of intermediate connections and other good practices will provide a high Margin Link that will ensure your installation against future signal losses.ANY DOUBTS? QUERIES? WE ASSIST YOU
PROMAX is a leading manufacturer of test and measurement systems, broadcast and TV signal distribution equipment. Our product lines include measuring instruments for cable TV, satellite TV, broadcast, wireless and fibre optics networks, FTTH and GPON analyzers. DVB-T modulators, IP streamers or IP converters (ASI, DVB-T) are among the company’s latest developments.