Marco, In Maryland, to get 270mbps reliably, I try not to do any link in 11Ghz beyond 10 miles or so with 3ft dishes, to get 99.999%. Rain fade calculated at about 18db fade in that situation. But still, in heaviest rain, I dropped link a few times.
Obviously with lowest modulation, larger dishes, and lower 9 expectations, in dryer climates, you can go much much farther. Using DragonWave's tool, with Greenville, TX rain data, 6ft dishes both sides, Highpower (19.5db), 40Mhz, model HC277, you show -42dbm with about a 17.5db fade margin, listing 99.978% uptime. (Trango's APEX or GIGAPLUS probably does as far if not farther, I just didn't have the Trango tool handy while writing this) My point here is, your link has 17db rain margin for a 27mile link in an area with a higher rain rate (I think around 66mm/hr), accomplishing a lower fade margin than I have for my 10 mile links here in Maryland where the rain rate might be around 48mm/hr. So... same fade margin, but your link three times longer. Your link will likely drop much more frequently. But will it? There is a misconception that a link three times longer could have three times the fade, which is not true, because the rain causing the fade rarely covers a wide area. For example, the rain storm might just be raining over one mile of the path, regardless of the length of the path. What is a critical factor is the direction of your link, and the likeliness of whether the Rain storm would just cross your link path once (moving perpandicular), or whether rain storm likely would travel along the path of your link in parallel. If the storm followed the path of your link, moving 1 mile at a time along the path from one end to the other, the duration in which the rain storm would effect your path would be much longer. So not only is it useful to predict the heaviest rain and duration in an area, but also the directions storms likely move. That was a mistake I made... I have a backhaul three cell sites in a row 10 miles apart, and almost always when a storm comes through, it hits each and every one of the three tower one at a time after each other, as the storm migrates. Thus, if a storm causes an outage it causes it three times, once for each link it hits. If my towers were aligned perpandicutlar, I'd have one third the amount of outages or downtime. So yes, the 27mile link can be accomplished with 11Ghz. But yes, you will have some downtime, and you need to deside if that can be tolerated for the link's pupose. At Full modulation the tool says 728min of outages. You'll have to rely on adaptive modulation, and the lower modulations speeds during rain and fade. At 100mbps it has 37db fade margine, the downtime drops to only 40min/yr, (99.997%) which is way more acceptable. You can do some calcs and see that if you changed the design to be three 19 mile hops, and the uptime would go down to only 11 min/yr w/ adaptive modulation down to100mb. But then, you'd have 1/3 more expense. I guess this boils down to whether your need of capacity versus uptime is more important. a 100mbps 5.8Ghz or 6Ghz link will have much better uptime at 27miles. If you need higher capacity, then 11Ghz will give it to you, most of the time 99.97% of it, but you'll have some occassional down time. What I'm learning is to both 1) trust the path calc tools, but 2) also to realize there are other factors that can degrade the real world results, and should look at the tool as being the best case. Thinks that can contribute to worse are.... antennas that move, antennas that get misaligned, noise that develops, cables that fail, adaptive modulation or rebooting slow to respond, that could result in additional or premature downtime. Tom DeReggi RapidDSL & Wireless, Inc IntAirNet- Fixed Wireless Broadband ----- Original Message ----- From: "Marco Coelho" <coelh...@gmail.com> To: "WISPA General List" <wireless@wispa.org> Sent: Tuesday, September 28, 2010 12:51 PM Subject: [WISPA] 11GHz fade margin > I'm looking at deploying some 11GHz gear. I would like to do one path > in two 27 Mile Hops. Using 6' dishes I show a fade margin of 19db. > Is this adequate for 11GHz at that rage? At 5GHz - 6GHz, I would be > fine with it. > > Is anyone else pushing 11GHz this far? > > -- > Marco C. Coelho > Argon Technologies Inc. > POB 875 > Greenville, TX 75403-0875 > 903-455-5036 > > > -------------------------------------------------------------------------------- > 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/ -------------------------------------------------------------------------------- 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/
