Thread: Confused
View Single Post
Old 1-Sep-2010, 8:05 PM   #2
Dave Loudin
Senior Member
Join Date: Jan 2010
Location: King George, VA
Posts: 659
The forum where you typically ask for help is "Help with reception." Perhaps this will get moved there. In the meantime, some basic concepts:

1) Digital TV receivers need a minimum signal strength above background noise in order to decode a picture. The ratio of signal power to noise power is call signal-to-noise ratio (SNR or S/N). The standard for digital TV calls out the SNR that all receivers must be able to use.

2) TVFool predictions use this minimum SNR to establish a reference for the noise margin, or NM. If a signal is predicted to have an NM of 0 (zero), then, barring any other losses, a receiver will successfully decode it.

3) TVFool's prediction model doesn't take into account every possible way a signal can fade or be interfered with. Therefore, we like to add some additional margin by recommending designing to an NM of +10.

4) Antenna gain adds to NM and signal losses in the cable between antenna and receiver subtracts from NM.

5) A pre-amplifier will zero out cable losses, but will otherwise not add to NM. In fact, the internal noise of the pre-amp will subtract from NM.

6) The "Real Channel" is the actual channel stations are broadcasting on. The "Virtual Channel" is what your TV will map the broadcasts to.

7) Many stations broadcast "sub-channels" that offer different programming from the main program. To see a complete list for your market, go to this site, click on Tampa, then click on "expand all". It will take a moment for the screen to update.

I can't see your report right now, so additional advice will have to wait.

Last edited by Dave Loudin; 1-Sep-2010 at 8:22 PM.
Dave Loudin is offline   Reply With Quote