One of the most common problems that installers encounter is when the output of the amplifier contain more distortion than the input signal. Usually this can be attributed to a couple of factors; sometimes it is a faulty amplifier. However, it is more likely the amplifier is being overdriven by the input signal. This can have many detrimental effects on the output signal including clipping, intermodulation and increased phase noise.

A common masthead amplifier will amplify signals at about 34dBuV and have a maximum output of around 104dBuV. Even though this doesn’t sound like much gain and the output level seems more than adequate for any domestic application 3dB is still a doubling in signal so 34dBuV is a huge gain in signal strength. More than what is required at most doemstic job sites.

If the installer has a signal strength at the antenna of 72dBuV and wants to distribute this signal to more than 6 or more outlets he will have to amplify the signal off the antenna. The issue here is that if the input is over 70dBuV he will overdrive the amplifier causing the picture to breakup and distort.

The equasion we use find if the amplifier is being overdriven is relatively simple:

Max Output – Gain = Max Input   (104 – 34  = 70dBuV)

If your max input figure is more than the amount coming off the signal source we have a problem. There is a couple of ways to solve this:

.Install an amplifier with less gain (22dBuV will still be more than appropriate in this application)
.Turn down the gain pot on the amplifier so the input level is not over the max input.

Usually it is better to use an amplifier with lower gain if possible because of the lower noise and distortion figures that are usually assiciated with low gain amplifiers. It is very important to keep to the guiding rule : if you don't need a high gain amplifier, don't use one. Sometimes it is better to use a low gain high quality amplifier, bigger doesn't always mean better.