ATV P-Level reporting
When you watch an ATVer's picture, you would like to tell the sender conveniently how
well it is being received. You could say, "Your picture is 20% snow", etc. But
that terminology is very vague and wordy. The only exceptions are "I can't see it at
all" or " You're perfectly snow free" which, we all understand very well.
It's analogous to the digital 1's or 0's indicating "On" or "Off" but
it's the "shades of gray" that become a bit more arbitrary.
To solve this the
"P" system was developed for AM signal reception. It goes like this.
"P" stands for picture level and is broken into six levels from P0 to P5. A
signal received as P0 is recognizable to its existence only. No detail is discernable and
usually only sync bars can be seen in the snow. Experience has demonstrated that the
minimum recognizable signal change is about 3db (2:1 power change) so 6 dB/step is
easily recognized and represents sufficient precision. The numbers continue in 6 dB steps
to P5, which is a snow free signal and 30 dB greater than P0. Beyond that, we tend to be
complementary to the sender, such as, "P5 plus", "broadcast quality",
Everyone likes complements and ATVers are no exception so if you like what you see,
tell the sender about it. However, try not overdoing it. P-unit reporting is universal
across the USA and in other countries as well. (Remember the P-unit reporting system is
accurate only for AM modulation because of the near linear levels. P-unit reporting of FM
signals can be used as long as it's understood that it will not be 6 dB/P unit because of
the non-linear nature of the receiver detection system). For a visual representation of
what the AM signal for each P-unit level looks like, see figures below . The
patterns are sized for best viewing at 640 x 480 but can be viewed at resolutions up to
1024 x 768.
P0 - This picture is barely recognizable. Only Sync bars can be seen.
Call letters are not visible.
P1 - Signal strength 6 dB stronger than P0. This represents sender power
level 4 times stronger. Picture recognizable but extremely snowy.
P2 - Signal 12 dB stronger than P0. Picture easily
recognizable but lacks detail and still quite snowy.
P3 - Signal 18 dB stronger than P0. Picture detail is much better
but snow is still visible.
P4 - Signal 24 dB stronger than P0. Picture detail is
better with very little snow.
P5 - Signal 30 dB stronger than P0 and represents a 1000 times
stronger power level from sender. Picture is snow free.