Isn't this only true for UHF? I gather that post transition in the US they discovered that VHF-HI requires about 10 dB more power than anticipated and VHF-LO requires 15 to 20 dB more power than anticipated.
Recent "findings on the ground" finally forced the FCC to reconsider their "assumptions" re VHF.
Part of the problem has been a dearth of (believable/repeatable/comprehensive) data re
Man-Made Impulse Noise,, esp. it's effect on DTV
and "Land-Use and Local Clutter (LULC)" Clutter Loss.
And the FCC's reliance on old ANALOG experience re requisite signal levels....but Digital is apparently
MORE susceptible to Impulse Noise (long glitches) than Analog (small visual defects).
On the other hand, recent ATSC Tuners have dramatically IMPROVED the ability to handle
Multipath, compared to the tuners used in ALL of the earlier On-Air tests.....so the 15 dB SNR
"minimum" for ATSC is probably closer to REAL OTA in current tuners (+/- 2 dB), whereas
earlier tuners might need 2-5 (to infinity) more SNR, depending on local multipath conditions.
I've seen some "Brazil" Multipath On-Air capture tests succeed with less than 15 dB SNR,
indicating that the Multipath components were being coherently combined. If two equal
strength signals (each at 12 dB SNR, with multipath delay between them) is coherently combined,
they could act as one signal at 15 dB SNR. [Hence F/B Ratio not as important to counter multipath???]
BTW: FCC OET-69, "Longley-Rice Methodology for Evaluating TV Coverage and Interference"
ignores BOTH of these important factors, although it is described in detail in FCC OET-74,
"The ILLR Computer Program", stipulating ZERO correction for VHF and typically 7 dB correction for UHF.
But both ASS-U-ME the Thermal Noise floor is never exceeded.......[cough....cough.....]
Here is what the FCC said about "Urban" (Man-Made Impulse) Noise in FCC-00-185 (22May2000):
"Additionally, several parties recommend that we modify the ILLR model to account for urban noise
on the basis of the measurements of noise included in the Rubinstein report. However, we believe these
are matters of signal quality rather than intensity. In this rule making we are concerned with the ability
of the ILLR model to predict the availability of signals of a specific intensity as directed by Congress,
and we decline to extend the scope of the issues addressed in this proceeding to include signal quality."
But Rubinstein only tested LULC on 162, 460 & 860 MHz and Urban Noise on (only) 162 MHz in four
locations (NO data for Lo-VHF).
Clutter Loss ranged from 10 to 17 dB on BOTH 162 and 460 MHz, but measurements were incomplete.
"Environmental" Noise on 162 MHz was 11-16 dB above Thermal Noise in Watcom County, WA and Atlanta, GA,
rising to as high as 18 dB above in the Southern California (L.A. & San Diego) areas.
[Note that Rubinsteins's results conflicted with several other similar LULC tests!!!!!]
[They reported several problems with data collection, tossing out lots of suspect data.....]
[No statistics re Noise levels....are they Average....or Peak....or something else.....]
[And their choice of 162 MHz is not explained....perhaps Noise included BAND USER signal levels???]
It is well known that VHF Man-Made Impulse Noise can be 10-40 dB HIGHER than the
Thermal Noise Floor, increasing towards the lowest frequencies, as depicted in Figure 10,
ITU-R Rec P.372 Noise Charts (former CCIR 322, apparently STILL ignored by FCC's OET Group):
Yikes, ITU wants 40 Swiss Franks for a fraking copy.....so see "Fam" in the fol. Figure 2:
But how does one calculate a statistical "coverage" for Impulse Noise, when it varies depending
on distance from overhead power & other lines and will also vary from house-to-house, depending
on whether using fluorescent tubes, brush-type motors, dimmers, arc-welders, ad nauseum.
And DURING a nearby lightning storm, each strike will kill nearly ALL reception....
Clear, concise technical arguments were presented re the need for ILLR Propagation Model improvements:
Which were argued AGAINST, mostly because they were presented by Dish Network's hired experts,
who were immediately discounted since Dish Network was trying to expand their Network viewers.
[A clear example of Politics trumping Engineering....but avoided very protracted court arguments....]
Ultimately, in FCC-05-199, FCC decided to do NOTHING wrt ILLR changes (avoiding the quagmire):
Only recently, did they encourage power increases for Hi-VHF.....