Antenna "Amps"

[mcq]

Is there someone who can give us a small primer on Antenna Amps and Preamps. I went to buy a "flyswatter" and found skads of options for both.

Related question, How many time should I be able split an antenna signal?

Thanx

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Patrick K. McHugh MBA MCSE
mcq@mc-hugh.com
Sony 61HS10 (4x3!!!!)
RCA DTC100
Pioneer VSX-D710S Receiver
Infinity 5.1 (passive) Speakers

Intel 1.8ghz P4 w/ 512mb Memory
Digital Stream HiDTV Pro
ATI Radeon 8500 Dual Monitor Video
Viewsonic (Analog!) 19" monitor
ADI 17" MicroScan Panel
SB Live Platinum
Cambridge Soundworks Desktop 5.1 Speakers

I must be a real techno-geek as I have two full HDTV setups, one acting as a DVR!

[Gregg Lengling]

Okay there are different amps you are talking about here...there are Preamps...these go at the actual antenna and you have a power supply in the house (usually with a gain control) to power the amp.  This power supply should be fed directly to the antenna coax with no splitters between the antenna and the preamp (if you do you will short out the power supply unless you have a special isolated splitter).  Gain is not the biggest item to worry about in a preamp, the Noise Figure is....average preamps have about 16 to 22 dB of gain (adjustable), and a good one will have a noise figure of less than 1.5dB (most normal ones have a Noise figure of about 3.0dB).

There are problems with preamps and you will probably want the adjustable gain control somewhere in your viewing room.  While they help with weak signals (read Fox6) they can cause havoc with stronger signals.  They cause intermodulation on stronger signals...and while you may have a signal strength on reciever of 90 or more, the signal is so distorted you will not be able to decode it...hence you will want to be able to reduce the gain for the high power stations.  (In theory it would be better to multiple antennas and coax runs and only preamp one antenna for those weak stations).

The second kind of amp is a "Line Amplifier", this is normally used to make up for losses in long coax runs and multiple splits.  When using a splitter you lose signal each time you split.  A 2 way splitter will have about 3dB of loss on each port (3dB is 1/2 power), so if you had a 10 microvolt signal, you now have a 5 microvolt signal on each lead....a 3 way splitter will have about 7 dB loss and a 4 way will have about 11 dB loss and so on and so on.   This is where a line amp helps....BUT.....it is important to have a clean signal available at the amp point or you will just aggravate problems.  If you have severe multipath or IM distortion the amplifier will amplify this and make matters worse.  I would stay away from line amps unless you have a clean install and know how to add traps for overpowering signals...it's possible to have 1 huge signal from one station that will destroy all the channels around it if you amplify it.


I hope this helps Patrick and good luck.


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Gregg R. Lengling
RCA P61310 61" 16x9
HiDTV Pro 2 computer reciever card
glengling@ameritech.net