Signal Quality and the RF Front End
RF Front End
Did you know that every digital system has what is termed as an “RF Front End”?
They do! The RF front end refers to the signal reception portion of anycommunication system – both analog and digital systems. The RF front end consists of the antenna and the cables that deliver the signal to the receiver. With satellite the antenna is the dish, and with OTA broadcast it is the TV antenna.
Each individual’s in-home system performance is determined by how well the signal is received at the RF front end. It is the integrity or quality of the arriving signal delivered to the receiver that will determine the performance of any digital system.
The goal of a properly designed system is to maintain the integrity of the signal as it is received, decoded, and presented. Everything about these systems (performance, reliability, and picture quality) is dependent on the quality of the signal you have to work with.
The measure of performance of a communications system is called signal quality or signal fidelity. Signal quality is a simple relationship of signal power to noise power. It is called, signal-to-noise ratio or SNR.
Signal quality (SNR) meters are found in many television receivers and are typical with satellite systems. The value usually expressed on signal meters is not signal strength, but signal quality, or SNR. Some receivers have both signal strength and quality readings.
I hear many of you saying, “We are using digital systems and BER (bit error rate) is what counts.” Truly, BER is the term applied to describe digital system performance. What we need to realize is that BER is a function of SNR. In other words, SNR determines BER. They are tied together and cannot be separated. (I’ll post “Interpreting BER?” next.)
As SNR increases, BER decreases (good). As SNR decreases, BER increases (bad). What we have failed to realize is that as the SNR decreases, the number of errors and the rate of errors increases. The greater numbers of errors that result from lower SNR all have to be corrected or covered by the FEC (forward error correction) algorithms – the coding and decoding of the signal.
The greater the amount of errors that need to be corrected in a bit stream, the further from the original quality will be your end result. FEC corrects or ‘diminishes’, or hides errors to the best of its ability. For it to correct errors there needs to be enough good redundant information to replace or correct the corrupted bits. In the absence of all the right stuff, FEC uses its tricks and tools to interpolate (guess) the correct information from what’s left. The more errors you have means the more guessing the FEC has to do. Every guess is one step further from the best quality available.
There are two ways to affect the signal quality or SNR. The first way is to increase signal strength. The signal quality (SNR) will be increased and the BER greatly decreased, by even a small increase in the signal strength. The second way to increase signal quality is to reduce noise. Either of these actions will result in greater signal quality and better performance, but the “biggest bang for the buck” is increased signal strength.
Don’t fall for the “as long as you have lock” mentality. First maximize your signal, then pay close attention to proper installation to further preserve the signal received. Every bit of noise injected by lack of grounding, poor connections, or improper materials, robs you of just a little more of the all important signal quality.