Bridge Grounding Protection- Lightning Arrestors

[edwardsjj]

Next month, I'm setting up my first bridge with 1310 units using Yagi's. I'm concerned about how much grounding I should do for protection. I procured lightning arrestors to use between the Yagi's and the antenna extension cables. My question is, is this enough grounding to protect the units? Thank you for any assistance.

[scottmac]

NO, not really.

Calling those things lightning arrestors is like calling a single layer of cardboard a "Bullet Proof Vest."

They are meant to allow static charges to bleed off from the cable (built up from wind + dust / snow in dry environments), to (somewhat) dissipate the ion charge that follows the thunderclouds (and ***possibly*** make the device less "visible" to the lightning, and to dissipate electromagnetic energy from "near hits" (as long as they are not "too near").

For any external system, IMO, your best bet is to include a segment of fiber between the AP and the rest of the LAN. The segment of fiber will keep the lightning from killing the rest of your network (and maybe phone systems, depending on the layout of your data center).

It can be as simple as a copper / fiber transceiver pair in the run to your AP. Media converters / transceivers are ~US$100.00 each, but, if you get hit by lightning, will save you some serious grief.

CDW (www.cdw.com) has a fine variety of media converters ... I'm sure there are a number of other outlets as well.

Do not relay on the "Lightning Arrestors" for anything beyond light static discharge. Even when installed 100% correctly (and they usually aren't), they won't save you from "The Big Event." Only isolation will save the rest of your LAN.

Good Luck

Scott

[edwardsjj]

Thank you, Now I'll get a media converter and use fiber segment.

But that raises another question for you. This is a very high profile installation within my company, I want it to work smoothly.

I understand in a bridge design the connections should be kept to a minimum. IYO, should I just forget about using the lightning arrestors? Thank you for all your assistance.

Jimmy

[scottmac]

Again, no (make it a capital no, with a few exclamation points for effect ... it's been a long day and I'm too tired to get expressive ;-} )

First, it's likely that your local electrical code for your area requires it. The National Electrical Code (probably) requires it (I don't remember), and it's a very good idea to use it.

While it's assigned label ("Lightning Arrestor") is unfortunate and ~misrepresentitive, it does perform a useful-to-vital function in protecting you, the users of the network, and some/most of your networking apparatus.

It does permit the bleed-off of static, it does offer some protection from (not to) near lightning strikes. There is still a significant EMP from local lightning.

The caveat is that the grounding system must be installed carefully and to-spec for any protection system to be effective.

If you're interested in environmental protection systems (ala lightning, static) check out Polyphaser (http://www.polyphaser.com/kommerce_products.aspx).

They are suppliers of the kind of equipment used by radio stations (AM, FM, private repeater systems, municipal radio systems, etc) that keeps radio equipment on-the-air, even after a direct strike. This is not the kind of stuff you'd use for a wireless bridge system per se, but they have excellent documentation (and a excellent "for sale" book) on protection that will absolutely make you aware of "how to do it right."

While there is loss wth the addition of any additional connections at these frequencies, there are some you just have to live with; the system and the saety of your users (and yourself) are worth the sacrifice.

Good Luck

Scott

(BTW: Using the fiber link will usually permit you to move the bridge units closer to the antenna to make up some of the losses from the protection devices).

[edwardsjj]

Thanks, I procured two media converters so; to include a fiber segment on the root side. But this brings up another question, and I need your advice please.

I'm setting up the bridge next week, the Yagi is already mounted on a pole outside the building and the network RTR/switch is rack mounted inside, only 65' ft away.

Question is, How long length does the fiber segment need be? IYO, how should I configure the cables? [I've got a 50'ft Cisco antenna cable, a 1’ ft and a 20' ft power injector cable for the root unit, and various length fiber and copper patch cords]. Thank you for any advice.

[scottmac]

It's a little had to say without seeing the site, but you're probably good with the 50' cable to the Yagi, then the short cable chunk to the PI, then fiber as possible to the computer room / closet / rack.

My personal preference is to keep the lightning as far away (and outside,) as possible.

If the 50' cable is way long, and you have someone that can do proper coax termination (at these freqs, proper termination is critical ... it could cost you your radio), then shorten it up.

I think you mentioned that the other building is ~100 meters away, but having the extra signal margin will come in handy during the spring rains.

Good Luck

Scott

[edwardsjj]

Sorry, I didn't explain my question well. I have TWO media converters, that's a converter for each end of the fiber cable.

I understand I should connect the Yagi to 50'cable to Bridge to 1’ ft cable to PI.

But, there is an RJ-45 interface out of the PI and a RJ-45 port into the network switch. So, I bought two media converters as to have a fiber segment.

My question, how long length should I make the fiber segment? In other words, should I have more fiber cable or more copper cable?

Thank you, I appreciate your opinion.

[scottmac]

If you have the fiber, make that your major run.

At the least, if you have enough fiber, use the distance to get the copper-connected components from the outside (like the power injector) as far away from you your inside LAN as possible ... isolation is a good thing if your layout permits it.

I think the minimum distance for the fiber link to be "safe" is ~one meter ... longer is probably "safer" ... and there may be a minimum spec for your converters ... check the docs.

Good Luck

Scott

[edwardsjj]

Great,Thanks! One last question.

Coming out of the network switch RJ-45 port is copper cable, going into the media converter for the fiber segment. My question, can the media converter physically sit on top of the switch or should it be physically located out of the LAN closet away from the other equipment. In other words, can the copper cable be 1’ft or should it be longer length. Thanks for all your help.

[scottmac]

You can put the converter on top of the switch, strap it to the rack, whatever ... fiber will not conduct anything but light.

Be advised though that the general recommendation for UTP minimum length is (preferred) one meter, with a half meter (~18") being the absolute shortest.

I don't recall specifically, but I believe it relates to the feedback loops, bit times, signal strength .... something like that.

Good Luck

Scott