Do I need a preamplifier for my antenna? (CM-7777HD, CM-7777, CM-7778)


Please use the attached diagrams at the bottom of this article, to assist your understanding of the proper connections in your antenna system. 

A mast or antenna-mounted amplifier (preamp) is used primarily to overcome the loss in the coaxial cable between the antenna and the TV set.  In areas distant from TV transmitters, overcoming this loss is necessary since the signals are already weak.  In areas close to TV transmitters, a preamplifier is usually not needed, and can actually cause problems as it may cause the signal levels to be too high.

The only sure way to determine if a preamplifier is needed is to measure the received signal levels with a field strength meter.  Since this is not usually available for most home installations, determining the correct preamplifier can be a challenge.  One good way to determine if a preamplifier is needed it to enter your address into the Antenna Selection tool and review the listing of available channels at your location.  If the station you want to view is in the Red, Grey you most likely will see an improvement in signal strength by installing a preamplifier. 

Another possible need for a preamplifier will be on installations with long coaxial cable runs from the antenna to the TV set.  If there is 50 feet or more of cable between the antenna and TV set, a preamplifier may provide an improvement.

One more situation that may benefit from use of a preamplifier is when multiple TV outlets are being fed from the same antenna.  Since the splitter used to connect multiple TV sets causes signal loss, a preamplifier at the antenna can help overcome these losses by increasing the signal levels coming from your antenna. 

Preamp's cannot be used with Amplified Antennas.

Channel Master provides three preamp's with different amounts of gain. The CM-7778 has 16 dB of gain. The CM-7777 has 30 dB of gain. And our Amplify (CM-7777HD) has a 17 - 30dB adjustable gain setting.  In most cases when the channels you are trying to view are in the Red zone, the CM-7777HD on the low gain setting should have sufficient gain, even when feeding up to four TV sets, as long as the coaxial cable lengths are not excessively long.  For Blue zone, and especially Purple zone, channels, or in installations with very long cable runs and a high number of TV sets, the CM-7777HD on the high gain setting may be the better choice.

For Red, Blue, and Purple zone channels, it is preferred to use a preamplifier at the antenna instead of a distribution amp/drop amplifier in the house.  The reason for this is to ensure the amplifier is receiving sufficient signal levels.  If the signal levels are already bad at the input to the amplifier, they will not be improved by amplifying them.

In some instances, it may be necessary to use both a preamplifier at the antenna and a distribution amplifier inside the house, but in most installations, there is no advantage to using both at the same time.

In Yellow, Green, Light Green, and some Red zones, signal levels are usually strong enough at the antenna that a preamplifier may not be required.  However, for multiple outlet installations and long cable runs, a distribution amplifier is recommended to ensure that signal levels to each outlet are maintained at high enough levels to prevent drop out of the TV signals.

Installing a Preamplifier

A preamplifier consists of two units: a preamplifier and a power supply.  The preamplifier itself is mounted on the antenna boom or on the mast as close to the antenna as possible. The power supply unit is mounted indoors. Power is supplied to the preamplifier unit through the coaxial cable. 

The preamplifier is located as close as possible to the antenna feed point because the weak received signal must be amplified before it is attenuated by the coaxial cable and splitter. Preamplifiers mounted farther from the antenna usually amplify (magnify) the interference along with the good signals.  

Preamplifier units come with U-bolts for easy mounting on the antenna mast.  After the preamplifier is attached to the antenna or mast, run a length of coaxial cable from the antenna output connector to the input connector on the preamplifier.  Leave enough slack in the transmission line to form a drain loop. This will keep water out of the amplifier housing.  

Next, run the coaxial cable from the output port of the preamplifier to the power inserter "TO AMP" port.  The coaxial cable sends power to the pre-amplifier. The power supply and power inserter are mounted indoors, usually near the TV set.   You'll need to connect a length of coaxial cable from the power inserter 'To TV' port , to the TV tuner input.

The last step is to plug in the power supply. Because it uses less current than an electric clock, it will not be expensive to leave it plugged in.

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