A preamplifier is a two part unit. One part (the amplifier) is mounted to the antenna mast near (usually below) the antenna. The second part called the power supply is located indoors. The preamplifier has a TV antenna coax cable input usually labeled "ANTENNA IN" and a coax cable output labeled "TO POWER" The down lead coax cable is ran from the TV antenna to the mast mounted preamplifier and from the mast mounted preamplifier indoors to the preamplifier power supply. The coax cable feeds into and out of both parts. The power supply requires a 110v electrical outlet. The function of the power supply is to convert the 110v to low voltage and supply it via the coax cable to the mast mounted preamplifier. For this reason a signal splitter should not be locate along the coax cable run between the power supply and the preamplifier. A signal splitter in line between the two parts will interrupt the flow of electricity to the preamplifier. If the voltage does not reach the preamplifier it will fail to operate causing poor reception.
A distribution amplifier is a single unit with both the signal amplifier and power supply built into the same housing. The distribution amplifier also requires a 110v electrical outlet. A distribution amplifier is generally used to boost the signal when distributing the signal to multiple TV locations. The installation location of the distribution amplifier is on the antenna side of the signal splitter. The coax cable feeds into the amplifier from the antenna and out of the distribution amplifier to the signal splitter and from the signal splitter to each TV.
Both the preamplifier and distribution amplifiers have one thing in common they both amplify the TV signal. However, generally their uses are specific.
A preamplifier is used in moderate to weak TV signal areas and generally is not used in strong signal areas. A preamplifier can enhance the performance of the TV reception. The preamplifier does not increase the performance of the antenna itself but the results appear to do so. The TV antenna receives the same signal with or without a preamplifier. Without a preamplifier you have to count on the signal strength gained (antenna gain) by the antenna to deliver the signal to the TV. For each foot of coax cable length the signal must travel from the antenna to the TV a slight amount of signal is lost. The longer the cable run is from the antenna to the TV the more likely a preamplifier will be needed. In other words, the preamplifier boost the TV signal of the antenna compensating for the signal loss that occurs getting the signal from the antenna to the TV. Generally speaking a quality high signal gain TV antenna can deliver a signal through a 50 foot coax cable without the need for a preamplifier. However, in weaker signal areas a preamplifier is a benefit even when there's a short cable run from the antenna to the TV.
More signal amplification (amplifier gain) is not always better. Simply put, you can't amplify a signal into existence that the TV antenna is not receiving or the antenna is receiving the signal but it's too weak to maintain quality reception. Too much signal amplification can be as bad as too little. The proper signal amplification is determine by figuring out the signal loss that will occur getting the signal from the antenna to the TV.
Below is a chart that will help you determine the signal loss that will occur in your TV system getting the signal from the antenna to the TV. The TV signal when refering to antenna gain, amplifier gain and signal losses is usually measure in decibels (dB). The end result is a plus 5 dB to no more than 15 dB of surplus signal at the end of the coax cable at the TV.
Signal Loss Chart.
- 2 way signal splitter 3.5 dB
- 3 and 4 way signal splitter 7.5 dB
- 6 and 8 way signal splitter 12 dB to 14 dB
- 50 feet of coax cable avg. 2.5 dB
Example: If your system has a 2 way signal splitter (-3.5 dB) and 100 feet of coax cable (-5 dB) occurring from the antenna to the furthest TV the total signal loss is 8.5 dB. The 100 feet of cable equals -5 dB and one 2 way splitter equals -3.5 dB resulting in 8.5 dB of total signal loss. The proper preamplifier will deliver at least a plus 5 dB plus at the end of a coax cable at the TV and preferably plus 10 dB but no more than plus 15 dB after the losses are deducted. The proper preamplifier for the above scenario would provide somewhere in the neighborhood of 18 dB to 20 dB signal gain. Using the chart above add up the total signal losses in your system that will occur between the antenna and the furthest TV from the antenna and choose the proper TV antenna preamplifier accordingly. If the signals are strong you may not want to use a preamplifier even though you are using a signal splitter. In areas of strong signals when a signal splitter will be in use a distribution signal amplifier instead of a preamplifier is a better choice.
A distribution amplifier is used to boost the signal strength and distribute the signal to multiple TV locations via a signal splitter. If the TV signals at your location are strong a preamplifier is not recommended. To supply multiple TV locations using a signal splitter in strong signal areas use a distribution amplifier. Install the distribution amplifier within a 50 foot coax cable length from the TV antenna on the antenna side of the signal splitter.
When it comes to signal amplifiers you usually get what you pay for. Lower priced amplifiers do not perform as well or last as long as the higher priced units. The main things to look at are the dB gain of the amplifier and the noise figure of the amplifier. Match the dB gain of the amplifier to accommodate your antenna system configuration using the chart above to select the correct amplifier.
The noise figure of an amplifier is consider good when it's 3 dB or below. The lower the number the better. Noise figures between 3 dB and 5 dB are mediocre and above 5 dB is poor.