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Discussion in 'Over the Air TV By RabbitEars.Info' started by freeisforme, May 24, 2017.
Has anyone compared coverage maps from tvfool.com and RabbitEars.info?
For the most part, they are different looks at the same data.
Unless you're an advertiser, I would imagine the only information that is really important is where you're antenna is located and that typically doesn't involve a large map.
If you live on a mountain top or at the bottom of a valley you might see a difference in signal depending on tvfool and rabbitears interpretations of data. On open "flat land" the signals are going to be very similar.
I reason that because the Longley-Rice model is used by both, unless one site has found different terrain data to operate on, they should both give the same numbers - just presented differently.
I can't find good information about what specific technical details go into the TVFool maps, other than the fact that they use the same SRTM terrain data the RabbitEars maps use. The RabbitEars maps are produced using the SPLAT software combined with modified versions of scripts produced by Doug Lung of NBC. I assume a receive antenna height of 4 meters, while the FCC typically uses 10 meters and that is a pretty standard value, so TVFool may be using that value.
Four meters seems a bit high (given the popularity of indoor antennas). Ten meters seems a silly default to me.
As the tvfool.com FAQ notes, if you really want the best forecast, the point-to-point model is much more refined than a map as it is calculated for the 3D coordinates of your antenna. tvfool's maps use 1,000' horizontal resolution.
4 meters might be reasonable. My yard is built up from the street, close to 2 meters. The blocks of the basement, rafters and flooring add another meter. Then close to a meter for an indoor antenna off the floor.
Do you consider your home configuration representative of what the average home is like?
Most homes are not particularly far above road grade which may be different yet from the survey data's reading on the topography. Remember that the tvfool maps run on 1,000' samples of the Shuttle RADAR Topography Mission data.
My home antenna is just short of 10M above grade because it is on a somewhat tall mast on my second story roof. My workplace antenna is a mud-flap style unit about 1.3M above grade. A typical Ranch Style home would be similar.
I think whatever choice is made, it is fine as long as it is documented (as all assumptions/economies associated with using models should be).
The 4 meters is designed to be a compromise value, assuming an antenna could be on the first or second level of a home. It's intended to fall near the ceiling of the first floor of such a home.
1000 feet? I'm used to hearing terrain discussed in seconds. 1-second terrain, which is what the FCC's TVStudy software uses, is about 30 meters (100 feet). That implies the terrain data TVFool is using is 10-second terrain, which I didn't think existed. The SRTM data used by SPLAT for RabbitEars is, to my knowledge, 3-second terrain.
The terrain detail available is certainly more finely grained, but the "resolution" that tvfool uses for their maps is 1000' according to the Coverage Map FAQ page (last paragraph).
While you can't reasonably make more accurate data from less detailed data, you can certainly sample detailed information down to whatever lesser level of detail you want to grind.
So, you believe that most people like having moats around their houses? Lots are graded away from the house and above street level for the purposes of drainage. Goes over some distance, so it doesn't look that extreme. Read up on the subject and you will see that a 1-2 meter drop is typical with a 10% grade near the house and a lesser grade of 2-3% further out.
Ah! I see. So he's using 3-second data, probably, with about a 3 point per km terrain extraction. That's kind of an odd number too. (FCC uses 1 ppk for coverage maps, 10 ppk for point-to-point.)
I actually don't recall off-hand what RabbitEars does. It's whatever the default for SPLAT is.
This depends entirely on local building codes and they vary widely. California and Oregon require only six inches of fall in the first ten feet (5% grade) from the footing. There are exceptions for special drainage situations.
Wisconsin building code (SPS 321.12) requires only 1/2" per foot for the first ten feet (a little over 4%). Again, there are special drainage situations.
Some new homes in my area appear to be almost level with the street. 25 feet away
New Jersey's code, R401.3, specifies the pretty common 6" in 10' drainage slope.
I haven't done enough tinkering with the point-to-point calculations to determine how significant the impact of elevation is.
My town only looks to see if there is standing water. we have sandy soil.
tvfool may not be updated. All the posts i have read are old(2014). I signed up over a week ago, received confirmation email and followed link to confirm, and still have not been given access to forums.. awaiting admin approval......I have emailed twice with no reply.
It took me 3 months to get approved when I first signed up. I think there's only 1 mod, and he is or was sick.