Eudora! Now there is a program I havent seen in years! On Fri, Oct 1, 2010 at 2:56 PM, Fred Goldstein <fgoldst...@ionary.com>wrote:
> At 10/1/2010 02:27 PM, Matt Jenkins wrote: > > What are the headings for your chart? I don't understand it.... > > > Eudora had trouble with cut-and-paste of the original document. > > The first column is height above average terrain, from x to y meters (10 > but less than 30, from 30 but less than 50...). The second is the proposed > distance outside of the protected contour of a co-channel station. THe > second (the small distance) is the proposed distance outside of the > protected contour of an adjacent-channel station. > > So IEEE 802's proposal (in a 2009 Petition) was to allow antennas above 600 > meters HAAT only if more than 68 kilometers outside of the protected contour > of a co-channel station, or 426 meters outside of the contour of an > adjacent-channel station. > > Not that those calculations were perfect; sometimes being precise isn't the > same as being accurate. TV broadcast interference is usually measured at a > fixed height, I think 10 meters above ground. If the antenna is 500m above > average terrain, it is probably more than 30 meters above ground. It might > even be on a rather tall tower. In that case, the signal level near the > ground will not be the same as the signal level in a straight line. So > there is probably no likelihood of adjacent-channel interference. > > I remember an FM station (WMSC) that came on the air around 1970, 2 > channels away from two another ones (WKCR, WFUV) whose protected contours it > was within. You had to protect second and third adjacent channels, which > normally meant 4-channel spacing, because receivers near to the antenna > would be clobbered (>20dB stronger). In this case the new station was about > halfway up an existing 1000-foot TV mast. So its signal strength at the > height that counted was so low that it did not violate the interference > rules for second and third adjacent channels. It is currently licensed for > 1W ERP at 205m HAAT. (But one of the second-adjacent-channel licensees has > still given them grief at the FCC.) > > > On 09/30/2010 08:13 PM, Fred Goldstein wrote: > > At 9/30/2010 10:37 PM, Jack Unger wrote: > > Fred, > > I'm sorry to seem dense but I don't understand your explanation below. I'd > appreciate it if you would re-explain. The FCC said: > > "transmit antenna used with fixed devices may not be more than 30 meters > above the ground. In addition, fixed devices may not be located at sites > where the height above average terrain (HAAT) at ground level is more than > 76 meters". > > I'm trying to reconcile that with your statements. Could you please > re-explain more clearly or by using better actual numbers (both HAAT at > ground level and antenna height above ground)? > > Thanks in advance, > jack > > > Sure. In the Order itself, the FCC explained the origin of the 76 meter > HAAT limit. They explained that they didn't want any antennas more than 106 > meters AAT. That's the maximum antenna HAAT I referred to. Since antennas > are allowed to be 30 meters above ground, they subtracted 30 from 106 and > got 75. See paragraph 66 of the Order: > > "We find that limiting the fixed device antenna HAAT to 106 meters (350 > feet), as calculated by the TV bands database, provides an appropriate > balance of these concerns. We will therefore restrict fixed TV bands devices > from operating at locations where the HAAT of the ground is greater than 76 > meters; this will allow use of an antenna at a height of up to 30 meters > above ground level to provide an antenna HAAT of 106 meters. Accordingly, we > are specifying that a fixed TV bands device antenna may not be located at a > site where the ground HAAT is greater than 75 meters (246 feet)." > > The Order cited an IEEE 802 Petitition > http://fjallfoss.fcc.gov/ecfs/document/view?id=6520201311 which called for > HAAT to be a factor. But they didn't call for a ban on operation above 75 > meters; rather, they wanted co-channel separation to increase with height: > > less than 3 meters | 6 km 0.1 > km > 3 Less than 10 meters* 6.9 km 0.256 km > 10 Less than 30 meters 10.8 km 0.285 km > 30 Less than 50 meters 13.6 km 0.309 km > 50 Less than 75 meters 16.1 km 0.330 km > 75 Less than 150 meters 22.6 km 0.372 km > 150 Less than 300 meters 32 km 0.405 km > 300 Less than 600 meters 45.7 km 0.419 km > 600 meters or higher 68 km 0.426 km > > That's rational. On the other hand I'd prefer allowing fixed devices at > any ground elevation, to allow everyone to subscribe, so I'd suggest instead > that they maximum ERP be decreased in order to limit interference to the > same level. So maybe 6 dB from 76 to 150 meters and 10 dB to 300 meters, > though that's a guess; I haven't run the calculations. And I'd allow > directional antennas, professionally installed, to have ERP measured in the > direction of the protected contour, with no reduction in ERP if it's clear > to the distance the above chart. > > I'm thinking about a petition to that effect. I have real subscriber sites > in mind. > > -- > Fred Goldstein k1io fgoldstein "at" ionary.com > ionary Consulting http://www.ionary.com/ > +1 617 795 2701 > > > > > -------------------------------------------------------------------------------- > WISPA Wants You! Join today! > http://signup.wispa.org/ > > -------------------------------------------------------------------------------- > > WISPA Wireless List: wireless@wispa.org > > Subscribe/Unsubscribe: > http://lists.wispa.org/mailman/listinfo/wireless > > Archives: http://lists.wispa.org/pipermail/wireless/ >
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