[rabbit73]

Hi, Zippy:

I see that ADTech beat me to it while I was typing, but I'll give you my answer anyway to supplement what he said. Maybe between the two of us we can turn on the light bulb for you.

I am trying to understand the relationship between NM and Pwr

I'll try to help you with what I've learned. Since you mention the reference, I assume you mean the TV Signal Analysis FAQ so I will not quote it but will try to give you my understanding of it based on my limited knowledge of your situation.

My area seems to get pretty weak and unstable signal

Yeah, I see that from your report, even if it isn't your exact location. Signals that are 1Edge and 2Edge have terrain interference, and should not be expected to be as reliable as LOS signals. All OTA signals constantly vary in strength, 1Edge and 2Edge more so than LOS signals, so you need a "fade margin" for SNR (Signal to Noise Ratio) above the minimum ~15 dB at the "Digital Cliff."

You can compensate for the Edge signal deficiency by using an antenna with a little more gain, but then the antenna will have a narrower beamwidth and must be aimed more carefully. That is the trade-off between gain and beamwidth. The antenna must be aimed at the transmitter for best signal quality to reject multipath reflections.

I am 60 miles out and although the terrain is pretty flat here

Well, seems to be flat, but it isn't. The curvature of the earth starts to affect signals at about 60 or 70 miles. If you click on a callsign in your tvfool report you will see a dark curved shadow at the bottom of the terrain profile. That's the curvature of the earth beginning to interfere with your signal. The transmitter is at the left end and your location is at the right end.

PWR is the predicted signal power....the PWR is the strength of the signal to my home from the tower?.

Correct; the signal power outside in the air at the height you specified without trees or buildings in the signal path. We often call it signal strength, but it is more accurate to call it power because it is stated in terms of decibels as dBm.

NM is the predicted Noise Margin.....I must have a NM at the TV of over 0 to receive the station

Also correct. The predicted NM is based on an antenna with 0 dBd gain (like a dipole). To that you can add the antenna gain and the preamp gain (if you are using one) to make the NM more positive, but you must subtract the NF (Noise Figure) of the preamp because it adds its internal noise that degrades the SNR of the signal.

I made this diagram to help me understand NM when I was learning about it:



And Calaveras made this NM chart:



Interpreting Noise Margin in the TV Fool Report
http://www.aa6g.org/DTV/Reception/tvfool_nm.html

When you are making an estimate of signals, you can make a similar one using signal PWR by adding your antenna gain and preamp gain to the dBm PWR in the report. I often like to do that because tuners drop out a signal around -85 dBm.

Notice that the difference between NM dB and dBm PWR is a constant of 90.9 dB, which is another way of looking at the ~91 dB in ADTech's post.