Using 2 or more Antenna Signal Amplifier, Can it be done ??? - AVS Forum
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post #1 of 5 Old 12-09-2009, 06:06 AM - Thread Starter
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Hello Forum,

I'm in Milton area and am using a Channel Master CM-4221HD which gives me about 28 channels (analog and digital together). Few day ago, I got a GE video signal amplifier (24 dB) and installed it and it effected my receiption considerably and now I can get a couple of more channels and the quality of my existing channels is improved as well. I wonder it is possible to gear up two or more of these signal amplifiers for strongers signal? I assume if I use two amps, the signal will be 48dB stronger and if use 3 amps, it perhaps will be boosted up for up to 72 dB. Now I want to know if doing so is not going to damage or even burn my TV's tuners? Up to what limit the signal can be amplified? Thanks for advice. Cheers.
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post #2 of 5 Old 12-09-2009, 07:38 AM
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Quote:
Originally Posted by digitop View Post

I assume if I use two amps, the signal will be 48dB stronger and if use 3 amps, it perhaps will be boosted up for up to 72 dB.

If antenna does not pick up a signal there is nothing to amplify. If what you are proposing were true there would be no need to install an antenna in the first place.

The purpose of an amplifier is to compensate for signal loss after then antenna. In addition a good preamp will have a better noise figure then typical TV allowing a smaller signal, at the antenna, to provide acceptable level to TV.

1) If receive signal strength is weak mount low noise preamp as close to the antenna as possible. You want amplifier to have as much signal to work with as possible.

2) Amplifier gain should be such that after factoring in cable, connector and splitter loss signal delivered to TV is about 10 dB higher then at antenna terminals. The reason is so TV noise figure can be ignored - only NF of preamp is important. Gain beyond that does not help and can actually harm picture quality, but will not physically damage TV.

More info here:
http://www.hdtvprimer.com/ANTENNAS/basics.html

/tom
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post #3 of 5 Old 12-09-2009, 08:59 AM
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Tschmidt's response is excellent! (Great link BTW!) The only thing that I would add is that sometimes you can add a "0dB" gain splitter (a splitter w/amp for a 0dB loss) at your main TV location if you have to divide the receive signal to drive several devices. But, even this would probably be unnessary in most cases. An antenna mounted pre-amp should have the gain to overcome all downstream losses by at least 10dB as described by Tschmidt.
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post #4 of 5 Old 12-10-2009, 01:39 PM
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I wouldn't write off this idea that quickly. I did a whole bunch of testing with my Chanel Master 7777 and posted the results here:
http://www.avsforum.com/avs-vb/showthread.php?t=1197789

Here is what I found using the exact same antenna setup with and without the amp:

channel ... Before ......... After
2 .............. 78 .............. 85
5 .............. 56 .............. 72
7 .............. 80 .............. 79
14 ............ 47 .............. 57
16 ............ 70 .............. 68
22 ............ 70 .............. 68
26 ............ 86 .............. 76
45 ............ 82 .............. 83
64 ............ 37 .............. 57

The pre-amp had no impact on the local channels, but it did have a large impact on the distant (50 miles) channels. I would guess that adding a second amp would amplify both the signal and the noise coming in from the first amp, but it would in effect make the antenna a little more powerful at getting the fringe stations.

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post #5 of 5 Old 12-10-2009, 02:02 PM
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Put bluntly, if the original signal is crap and you amplify it, you have amplified crap. What do you get if you amplify it again? Answer: Crap squared.

If a quality low noise pre-amp is not able to pull the signal out of the mud with sufficient strength and quality to be decoded, a second amplifier isn't going to help. It will just make the defective signal stronger (but still defective).

If, on the other hand, that first pre-amp is able to recover a signal of sufficient quality and strength that it's "good enough" at the output of the pre-amp for reception but of insufficient strength to overcome the system losses downstream, then an additional amp would be useful for distributing the signal to its destination.
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