900MHz antenna positioning / Lightning question

[Alex]

I'm trying to set up a DSL to 900MHz relay about 1 mile apart. I'm planning on using Trango 900MHz equipment; the base station is at ground level pointed up a long hill to the subscriber unit 400ft higher (1 mile away and behind a lot of trees) ; using an AW-15 directional yagi connected to a M900s, with PoE. I think for best results I should be installing the subscriber unit at altitude, maybe on a tower or fixed to a tall tree.

Any ideas how I would go about protecting both ends of this [still uninstalled] setup from lighning strike? The Trango stuff isnt cheap and I'd hate to have it get zapped.

[M/Q]

You may have some problems with this link. If you consider the Fresnel Clearance Zone the antennas are going to need to be at least 32 feet off of the ground for a 1 mile link. I am more concerned about ground clearance than tree clearance with 900MHz, but avoiding trees should be a goal as well. This link talks about the Fresnel Clearance Zone I was referring to.

http://www.terabeam.com/support/calculations/fresnel-zone.php#feet

Next the Trango device uses PoE and the inside connection that the Cat5 cable and power adapter connect to also has a ground connection. That needs to be connected to an earth ground that will be at the same potential as the antenna system on the roof.

As for the antenna system, you need to talk to the building inspector and insurance company that you use. They will have specific requirements and you need to follow them or your insurance will not pay for damages acquired from a lightning direct or near strike. This typically requires the mast that the Trango antenna unit is mounted to be grounded with a very large grounding strap, again according to the codes for your specific area. The more important point is as I mentioned earlier it needs to be at the same potential as the ground on the PoE injector. If not it will not matter if the antenna unit is grounded.

You mentioned an external antenna, there are lightning arrestors that go in the coaxial line that sacrifice themselves and route the energy to the ground previously mentioned. That will help protect the Antenna unit as I assume you are going to have that as close to the antenna as possible.

http://www.hyperlinktech.com/web/lightning_arrestor.php

And one last time, I can not stress enough as to the importance of getting the insurance company and building inspector involved. As a lifelong amateur radio operator, I have had my share of lightning strikes and the only for sure thing is that something is going to get damaged. One tries to control just how much damage occurs.

I also wanted to ask if the Yagi is in a radome? If not, are you where it rains alot or snows? The unprotected yagi will have issues with either of those.

[valenti]

I have been working with Trango 900 equipment since February (starting a WISP).

I am in Michigan, so lots of trees. My first testing was with the AP stuck on the back of my house, about 15' off the ground. I then drove around. I was able to get a good connection (at ground level) about one and a quarter miles away.

I agree with M/Z's comments about Fresnel zone, but in reality, your link has a good chance of working at ground level. I wouldn't even bother with the Yagi to start with - I was just using the built-in antennas.

For lightning worries, I would start with just putting the AP and SU inside the house (in the attic) or mounted on the outside of the house under the eave. I don't think that would increase your lightning exposure much.

I'm not familiar with that Yagi, but have used M Squared brand (m2inc). Their webpages show a $36 lighning arrester, I have purchased that for my silo site. They say it probably won't help for a direct strike, but should help for indirect strikes.

If you do end up with a tower or mast to raise it higher, M/Z's comments on grounding are accurate. I don't think you need to worry about a perfect connection, just get -75dBm or better and it should pass traffic 100%.

(my current setup has the AP at about 85' with an 8dBi omni and my house SU leaning against the exterior wall on the second floor. I'm getting about -70dBm and the connection seems solid. Distance is 1.4 miles)

You might have problems with 900MHz interference. I'm out in the country, it isn't a problem currently (but my competition is moving in with Canopy units that will blanket 900, we will see what happens). But I did do some sprectrum analysis with the Trango in East Lansing, pretty busy there, only one channel that might have been usable.

[valenti]

If you do mount the units outside, you probably want a ethernet surge suppressor in line. There are some models linked to on Trango's web site. It is a small box with 2 ethernet ports, one would connect to the radio, the other goes into the house. It also connects to a ground via another wire. It is usually located just outside the house, where the ethernet line goes thru the wall.

Motorola's Canopy line also has a similar surge suppressor, I plan on using theirs.
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Oh, have you considered building up your own AP and SU? A few months ago Ubiquiti released a 900MHz mini-pci card that uses 802.11 signalling. Look at Star-OS and Mikrotik. They both sell small computers that accept a mini-pci radio, have outside rated enclosures, etc. I think you could put one together for $400 at each end.

Probably more complex to configure (I haven't used them yet, but hope to order some soon). Beyond the cost, another advantage is that you can define the channel size. If you could hog the entire 900 license free spectrum, you can push 50Mbs thru them.

[expert007]

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Oh, have you considered building up your own AP and SU? A few months ago Ubiquiti released a 900MHz mini-pci card that uses 802.11 signalling.



I realize this post is old, but I'm trying to figure out what this means. I've been looking at Ubiquiti's 900MHz products and determining if this stuff is for a 900MHz backhaul link or if you can actually put these mini PCI cards into a laptop to enable 900MHz wireless from laptop to 900MHz laptop.

Thanks!

[valenti]

I realize this post is old, but I'm trying to figure out what this means. I've been looking at Ubiquiti's 900MHz products and determining if this stuff is for a 900MHz backhaul link or if you can actually put these mini PCI cards into a laptop to enable 900MHz wireless from laptop to 900MHz laptop.

Thanks!

I don't normally follow this forum, but a search brought me back ... technically I suppose it could be made to work with a 900MHz card installed in a laptop, but I don't think it would be very practical. You would need to deal with getting a 900MHz antenna connected somehow, the built-in antenna would be for 2.4GHz. And then you would have a laptop that only works with 900MHz access points. (and the ubiquiti card is larger than most mini-PCI cards I've seen, so it might be difficult fitting it in)

The Ubiquiti cards are usually used in single board computers (search for WAR, WRAP, ALIX or Mikrotik). They can be used for either point to point connections, or as an access point supporting multiple clients. It is very similar to a regular WiFi access point, just running at a different frequency.
These can be put together from parts for about $225 each, including the Ubiquiti card. (so the 900 gear is more expensive than 2.4)

For example, a WISP might setup a 900MHz access point in a wooded area. If one house had line of sight to a tower, it could use a 5GHz backhaul link, then perhaps five or six houses could be connected thru trees to the 900MHz AP on top of that house.

Oh, some people on this forum seem to think that these 900MHz radios need to be mounted 40' high to work, due to Fresnel zone clearance. I had a situation that a customer's link was being affected by interference from another wireless system. As a short term fix, I connected him to an access point 15' off the ground at my house. His end is about 20' high, this is using 11dBi Tranzeo radios. Distance is about 1.5 miles, terrain is flat, path goes thru at least one woods. While his signal isn't great at -84, it does pass more then 1Mbit, which is what I was selling him. (will switch him to a yagi soon for a better signal, eventually I'll change my tower over to this gear, but that means I have to swap radios for several people)

Personally, I'm trying to get away from building routers from parts, so I've started buying Tranzeo TR902 radios.