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Old 24-Oct-2019, 8:43 PM   #14
BrooklinOTA
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Join Date: Dec 2013
Posts: 38
Quote:
Originally Posted by rabbit73 View Post
Not exactly.

The preamp does not cause a signal loss of 2.6 dB. What would be the point of using a preamp if it caused a signal loss of 2.6 dB?

It does, however, add its own internal noise, called the Noise Figure or NF, to the signal that reduces the SNR of the signal coming from the antenna terminals. The greatest affect of this added noise would be on the weakest UHF signals. The preamp also makes all signals stronger before they travel down the coax to the TV.

But, all is not lost, because the Noise Figure of the preamp is usually lower than the Noise Figure of the tuner in the TV that comes after the preamp, so there is a net improvement of the antenna System Noise Figure.

Since the preamp is just after the antenna, it is at the beginning of the antenna system. This means that it primarily determines the System Noise Figure according to the Friss Formula.
https://en.wikipedia.org/wiki/Friis_formulas_for_noise


Here is an example of with and without preamp that shows how adding a preamp might make it possible to receive weaker signals:

Thanks! Colour me corrected! So that said, is it always good to introduce a preamp just after the antenna?
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