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needs more reliable sources....--18.104.22.168 02:10, 2 November 2006 (UTC)
what's the unit of r ? what about the fomula in metric ?
- I guessed it is "kilobarleycorns". Probably wrong, I suppose. What are the widths of the subsequent Fresnel zones, those "annular rings"? What are the widths at other than the halfway point?
- What do "maximum obstruction" and "recommended obstruction" mean? Gene Nygaard 04:29, 4 May 2005 (UTC)
This article needs to be generalized to include the optics usage. (Yes, I know, sofixit and all that. I don't have time right now, so I'll just mention it here for now.)--Srleffler 04:07, 21 March 2006 (UTC)
The link to "this page" above appears to be no longer reachable, but I've seen 43.3 elsewhere and had the same question. See this page instead. The 43.3 multiplier (for the radius in feet and distance in miles) may be the "obstacle-free radius", which is often taken as 60% of the Fresnel zone radius. Can someone verify this? 22.214.171.124 21:50, 25 October 2006 (UTC) Gerald Reynolds
General formula is fine, but numerical values only for optics in free-space
I haven't even checked the accuracy of those numerical prefactors, but people should be aware that the concept of a Fresnel zone applies as well to *any* wave phenomenon (my own familiarity with it is in acoustics). I'll change the article if and when I have time, but (1)it should be mentioned that those numerical values which people have been quibbling over are specific to optics in free-space---other values will show up for acoustics problems---still others for other wave-types in different media; or, (2) there should be *no* numerical values given, and simply stress that the formula yields different results based on wave- and media-type. --Smoo222 03:20, 21 March 2007 (UTC)smoo222
Should this page make any distinction between "Fresnel zone" and "Fresnel region" (commonly used in antenna theory)?
In antenna theory, the Fresnel region generally refers to a radial range of distances between the reactive near field (~2*lambda?) of an aperture, and the Fraunhofer region (2*D^2/lambda, where D is the largest dimension of the aperture). Within the Fresnel region, the radiation pattern of the aperture varies significantly with radial distance since the multitude of sources that constitute a given aperture cannot yet accurately be approximated as having a common phase center.
126.96.36.199 23:42, 21 March 2007 (UTC)Bill Shultz
This is written like a high-school science report. Please recast it in, at the very least, the passive voice.
Error in Attached Image
Currently there's a spurious '15m' above the '20m' on the bottom set of images. It seems to have been left in there by mistake. Xrobau 12:50, 10 September 2007 (UTC)
Article is written to refer only [or predominantly] to radio waves
The article, while apparently sufficient for radio transmitter/receiver problems, mentions almost nothing of other wave types, which of course the entire concept applies to. A specific example is that of mentioning "radio frequency line-of-sight": There is absolutely NO restriction to radio frequencies.
There is also a minor correction which should be made (I have no time to get it totally right), in that it is mentioned that "If unobstructed, radio waves will travel in a straight line from the transmitter to the receiver." This is true at some level of abstraction (that of infinitely high frequency -- the domain of "ray optics"), but *false in the domain where Fresnel zone concepts apply*. In other words, the Fresnel zone is exactly one of several concepts designed to deal with the fact that waves do not travel in straight lines, even when there are no obstructions!
Another suggestion (again, I'll fix it if/when I have time) is to mention the source/receiver reciprocity which is implied by the figures included in the article. For an arbitrary receiver location (imagine the _field_ from the source), the Fresnel zone does not pinch down as is shown in the figures. The "pinching" is a result of the _receiver's_ own Fresnel zone -- that is, its response to an oriented incoming plane wave because the receiver also has a finite width aperture, and an orientation. The cigar-shaped zone in the figures is the *product* of the individual Fresnel zones of the source and receiver, taken individually. Smoo222 (talk) 13:30, 31 March 2009 (UTC)Smoo222
Why is Fresnel pronounced "/frɛnɛl/ fre-NELL" in this article, but "(pronounced /freɪˈnɛl/ fray-NELL)" in the Fresnel lens article? Both refer to the same person. I'd fix it, except that I've always pronounced it /frɛz'nɛl/ (frez-nell). My attempt is probably incorrect, but it makes me unaware of which is correct.
Question about phase information
I don't understand the assertion that an obstacle in the first Fresnel zone will result in an interfering signal 0-90 degrees out of phase, 90-270 degrees if in the second zone, etc.
In the first place, surely the phase change associated with a path that goes from one antenna to point P on the surface of the first Fresnel zone to the second antenna is 180 degrees (one half-wavelength path difference).
In the second place, there will likely be a phase change associated with the object causing the interference. For a specular reflection (e.g., a plane surface many wavelengths in extent, such as a flat roof), the phase change will depend on the angle of incidence, polarization and nature of the surface (e.g., dielectric, highly conducting, etc.) and can vary easily from 0-180 degrees.
You are correct, this can be very confusing given that the information is erroneous. I saw a webpage that could be the source for this wrong information. I'll fix it to say 0-180 180-360 and so on and add that this is the path-length phase difference. Maxbezada (talk) 20:47, 30 January 2013 (UTC)