Noise margin clarification

[Phil Leeds]

I have read that the noise margin of a digital tv tuner is about 12-14 db. Therefore any signal strength equal to or greater than this will produce a quality digital signal directly from the antenna. Is it reasonable to assume that a preamp with a 2.5-3db noise margin will overcome all antenna signal db fluctuations between 3db-12db and continue to produce a good picture? I would enjoy Winegard sharing as much of your knowledge base as possible. Thanks!

[winegard]

Here is the response from one of our engineers...

The noise figure for much of today's single conversion tuners is about 7.5 dB VHF and 9.0 dB UHF.



The minimum usable S/N ratio to decode an ATSC digtial signal is 15.8 dB and in general conditions at the antenna, this is at a minimum signal of 170 uV in urban areas and perhaps as low 100 uV in rural areas. Using a preamplifier would require a signal level increase at antenna output equal to noise figure of the preamplifier, plus additional level for atmospheric variations. Therefore we suggest to people that the minimum usable signal level at the antenna should be about 200 uV or -14 dBmV.