No worries, I struggled with this at one time in the past...
The reference you gave isn't applicable to RF communications, it's for digital logic.
Pop over to the FAQs (
https://www.tvfool.com/index.php?opt...d=57&Itemid=78) where Andy describes the various calculated items and see if they clear things up.
Some basic assumptions upon which the TVFool calculations are based:
1) Assumed noise floor in a 6 MHz bandwidth is -106.2 dBm
2) ATSC specification is 15.2 dB SNR in channel.
Therefore, a signal power calculated to at -91 dBm will have a noise margin of 0.
However, the NM values calculated do not yet take into account the tuner noise figure and any insertion or mismatch losses in the system which must additionally be accounted for. Since tuner noise figures may vary widely (4-10 dB), a value of 6 dB is a common assumption for system operating calculations. Add in 50 ' of RG6 (2.5-3 dB) and you're at a requirement for almost 10 dB of extra margin required for a basic antenna, coax, tuner system.
If time permits, there's a very long thread over at AVS that covers much of the development period for this website's tools. It's an interesting read.
http://www.avsforum.com/forum/25-hdt...on-thread.html