5-Oct-2008 Format of Signal Analysis report has changed (NEW!)

After much deliberation, the format of the Signal Analysis reports has undergone a significant overhaul.  This may come as a shock to some long-term users of the site, but we hope that these changes will actually make things easier for most people in the long run.

What's New

Signals are now ranked by Noise Margin (NM) as opposed to dBm.

It's still a bit technical for most people, but this should make a little more sense than dBm.  Simply put, Noise Margin is your signal level (in dB) relative to the minimum level needed to watch a channel.  At negative NM values, you cannot decode / view a channel.  At 0 dB NM, you can just barely get the channel.  At positive NM values, you can receive the channel and have a bit of padding to help deal with multipath, interference, weather changes, and other random signal fluctuations.

NM automatically compensates for the differences in channel type.  There was some FUD circling around about poor digital coverage because of their much lower transmitter power.  However, the truth of the matter is that digital (ATSC) signals can do a lot more with less power than analog (NTSC) signals.  Comparing channels on the basis of NM puts analog and digital channels on nearly equal footing so that now the "all channels" plots can merge the two lists in a more meaningful way.  People should be less focused on the raw signal power because that's not what determines a channel's reception quality.

Power levels (dBm) are still listed, but they have been adjusted to align with expected "real-world" power levels

There was often confusion about how the F(99,99) models resulted in theoretical signal levels (like -110 dBm) that should be impossible to receive if you're comparing that to a thermal noise floor of -106.1 dBm and a minimum detection threshold of 15.2 dB for ATSC (meaning the cutoff should be -90.9 dBm).  This "conservative bias" has be eliminated so that values in the "Pwr(dBm)" column should agree more closely with the "normal" power levels people are used to dealing with and what they might actually measure on a spectrum analyzer.

Anyone who got used to the dBm scale from previous TV Fool reports will have to re-adjust their thresholds because the scale has changed.  On the plus side, everyone can now think in terms of Noise Margins instead of dBm levels.  This way, you don't need to keep separate thresholds in mind for analog vs. digital channels.

If people live very close to some transmitters, the power values in this column will be highlighted in red to warn them of possible overload conditions in their amps or receivers.  It's just an estimate, of course, since actual overload conditions will depend on antenna gain, antenna pointing, and overload tolerance of the electronics.

 The "Xmit(kW)", "-100 dBm", and "LOS" height columns have been removed

Some people were confused by the meaning of these columns.  Some even thought they needed an antenna of the specified height to get reception.  A few people found the columns useful for gauging terrain blockage severity.  However, the main reason for removing these columns was to create more real estate to make room for a larger radar plot and make it possible to list more channels per report.  Although it's always difficult to discard useful information, I think the tradeoff in this case was justified.  An alternate title for this news release might have been "So much information, Not enough space!"

The size of the radar plot has been increased

The new table arrangement has made it possible to increase the radar plot size.  This will hopefully make it a little easier to read the transmitter directions and channel numbers.  It will probably also show up better when printed.

The yellow highlight on VHF stations has also been made stronger so that more people will take notice if any of their locals are on VHF.  We just want to make sure nobody is caught off-guard by having the wrong kind of antenna!

Analog and digital transmitters are no longer red and green

The color coding has been changed to more of a purple and blue color scheme because the red and green text was sometimes being misinterpreted as being related to the background color and reception liklihood.  We also think the new color scheme improves readability, but that's just a subjective opinion.

The overall image size has been changed to 800x768

It is very important to us that the TV Fool reports are an acceptable size to be posted on the most common discussion forums relating to OTA TV.  We want to do our best to bridge the gap between the helpful people responding to questions and the people asking the questions.  The lowest common denominator among the biggest forums seems to be 1024x768 and 800x800, therefore, the largest size that should be allowed at all sites should be 800x768.  Previous TV Fool reports were 800x600, so this is an increase of 28%

This allows us to increase the maximum number of channels listed on each report to about 51.  The old limit was aboutn 35 channels, so this should be a big help to DXers or anyone else trying to explore the weaker channels toward the bottom of their lists.


We hope you'll learn to like the new changes.

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