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silverlake
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connectors?

Sun Jun 19, 2011 7:14 am

I can't seem to get any shielded connectors to work with any board. they will power up but will not pass data. anyone have the same problem.
 
silverlake
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Re: connectors?

Fri Jun 24, 2011 6:41 pm

I'll try the ubiquiti shielded connector to see if that fixes the problem. for the drain wire that I have in my cable I solder it to the connector head, that should work that way shouldn't it. also I do test the cable after it is made and with the connectors I'm using it still gives me the same results even tho the tester reads it fine.
 
packetguy
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Re: connectors?

Sun Jun 26, 2011 8:06 am

Be sure that you only connect the shield at one end; other wise you can get ground loops that interfere with Ethernet signals or, worse, damage your equipment. You should use the metallic connector on only one end as well (the end that is grounded).
 
silverlake
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Re: connectors?

Tue Jun 28, 2011 3:09 am

the style of POE that I use is the Laird tech POE 24i which has a shielded port on it and it grounds when you plug it in why would you not use the drain wire on both ends, in order to drain the static through the grounded POE down below.
 
lazerusrm
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Re: connectors?

Tue Jun 28, 2011 12:12 pm

Be sure that you only connect the shield at one end; other wise you can get ground loops that interfere with Ethernet signals or, worse, damage your equipment. You should use the metallic connector on only one end as well (the end that is grounded).

Bad advice, do not do this. Ever! Never Ever, to think that that is the correct way to use shielded cabling and connectors is wrong!

Shield both ends and Ground to earth. Always. never use STP directly from an outdoor piece of equipment into an indoor piece of equipment.

You should have a separate outdoor grounded poe injector installed outside at the building entry, and grounded to a lightning/tower ground point. which has

STP input jacks on the equipment side, and then use a standard UTP cable from switch -> POE injector. If you are not going to ground STP properly, dont use

it at all! :)

-Brad
Last edited by lazerusrm on Wed Jun 29, 2011 9:21 am, edited 1 time in total.
 
packetguy
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Re: connectors?

Tue Jun 28, 2011 5:57 pm

lazerusrm,

If you're connecting STP cable to an outdoor antenna, you absolutely do not want to ground both ends of the cable. A correct installation (rarely followed by todays seat-of their-pants WiFi installers) employs a Cat5e, PoE-compatible lightning protection devices (e.g., http://www.l-com.com/item.aspx?id=10033) at the antenna side of the installation, before the cable enters the building. You must ground this protection devices to a real earth ground, which should be via a separate #6 AWG wire. Note that the STP cable shielding IS NOT the lighting protection ground path. The STP shield and drain wire is only for radio-frequency interference (RFI) and electrostatic discharge (ESD) protection. If you can't find an existing ground, then you must run one to a reliable earth ground -- which may mean driving an eight-foot ground rod (http://support.radioshack.com/support_v ... /37710.htm) into the earth outside the building.

The antenna should have a metal lightning rod electrode extending a foot higher than the antenna itself connected to the same earth ground as the lighting protector. This can be any piece of pointed metal rod, but I recommend buying a lighting rod kit (e.g., http://www.glenmartin.com/catalog/lightning.htm), which provides all the correct attachment hardware to ensure the lightning rod connection is effective at diverting a lighting strike.

The ESD protection at the antenna end comes from the cat5e jumper cable between the antenna and the lightning protector. Generally this is only a few feet long, and in this case I recommend using a factory-built, outdoor-grade (waterproof, UV-resistant) patch cable, which will have metallic RJ45 shells on both ends. You can terminate your own, but factory cables will be better crimped and they are convenient and reasonably cheap.

For the cable segment from the lightning protector to the inside of the building, it is critical that you ONLY GROUND THE OUTSIDE END of the shield. If you ground both ends, you risk a ground path current loop that can cause signal interference, due to the ground level differences between the electrical system ground and the earth ground used for the lightning protector. This is why I say only attach the drain wire (and metallic shell) one one RJ45 in this cable segment (the outside RJ45). This also helps eliminate any stray induction voltage spikes induced by a lightning strike from entering your inside equipment.

I'm a longtime telco engineer with decades of experience installing all kinds of outdoor antennas and radios. I've seen many serious incidents where lighting destroyed equipment and even caused personal injury inside a building, due to improper antenna grounding. What I see today is uninformed installers hanging PoE radios with integrated antennas off a piece of shielded Cat5e with the drain attached at both ends. This is the definition of a lightning rod, and could easily get someone killed. As it is, I often encounter dead WiFi killed by ESD due to lack of proper grounding. Grounding STP to an inside device, such as an Ethernet switch or PoE injector, is not correct, or adequate ESD protection. The ESD potentials created by wind can easily overpower the very light-duty grounds in these devices. Only a properly grounded Cat5 lighting protector will deliver effective ESD protection.

I constantly hear the argument "but I've done it this way for years and never had a problem." The fallacy here is that the installer is rarely around to see the damage resulting from his shoddy installation work. As often as not, it's the inside gear that gets destroyed by ESD, helpfully guided into the building by the installers incorrect double-ended STP drain wire connection.

By the way, these are the same recommendations given by Ubiquiti, the seller of the cable you recommend:

http://www.ubnt.com/forum/showthread.php?t=7003
 
silverlake
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Re: connectors?

Tue Jun 28, 2011 7:46 pm

thank you all for your ideas I'll try the better grounding stuff to try to eliminate all the problems with boards going bad. I'll keep everyone posted on how it works out
 
lazerusrm
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Re: connectors?

Wed Jun 29, 2011 9:16 am

Welcome :)

Packetguy:

Sorry my post was a little obscure, and i was very tired when the post was made. my bad.

Your second post is more complete and i mostly agree with you. Your first post was ambiguous and wrong.

When you run a cable from a Switch to the Lightning Arrestor/POE, you do not use STP cable. UTP only. Why on earth would you use a STP from Switch ->

Outdoor POE only to ground one end? Or use STP period if you are only grounding one end? This makes absolutely no sense, since your cable then becomes

a rather large antenna, i disagree with doing it this way completely.

Higher end radio systems (Dragonwave, Bridgewave, etc) recommend it this way or similar*.

I agree with you on the lightning rod above the antenna, and proper radio/antenna grounding procedures absolutely.

-Brad

*References

http://wlanshop.sk/public/files/product ... eGuide.PDF (Dragonwave)

http://www.systemsupportsolutions.com/i ... Manual.pdf (Pg.13-15) (Bridgewave)
 
packetguy
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Re: connectors?

Wed Jun 29, 2011 5:15 pm

Lazerusrm,

Grounding the shield in STP at one end does not make it "a large antenna". The shield doesn't carry a data signal, and thus there is nothing for this "antenna" to broadcast. The signal is only within the twisted pairs, each of which makes up a balanced transmission line (http://en.wikipedia.org/wiki/Twisted_pair). The conductors in a pair have equal and opposite EMF, canceling out any net outgoing inductive effect, so they are not going to inject a signal into the shield either.

You asked "Why on earth would you use a STP from Switch-> Outdoor POE only to ground one end? " Here's the answer. The purpose of STP is to block external EMF from inducing dangerous voltages in the twisted pairs -- EMF resulting from any nearby lightning strike, including one to your radio's grounded lighting rod. Because the cable between the inside gear and the lighting protector (which should be near the antenna, not near the building entrance) is outdoors, it requires shielding to block these EMF spikes. Lightning-induced currents on the twisted pairs in any outside cable segment can cause spikes of 500V or more, and without grounding this can certainly destroy gear, even if you have a lighting protector. The STP shield has to be grounded to dissipate (drain) these spikes, and that is the function of the drain wire. You ground the inside-to-outside cable segment at the lightning protector, not at the inside equipment, to break the shield path into the building and protect the inside gear from these spikes. You ground the shield AT ONLY ONE END to protect the twisted pairs and inside equipment from ground loop current.

A ground loop is a continuous current flow between an inside electrical system ground and an outside earth ground (or between two different building grounds), and can be 20V or more. Also called common mode (CM) voltage, the ground loop voltage is the potential measured between the neutral (white) conductor and the safety ground (green or conduit) conductor of a building electrical system. When a cable is grounded to two different ground sources, this potential creates a current that then induces EMF in the cable. This can cause intermittent data problems and even equipment damage (http://tinyurl.com/voltloop). That's why you need aggressive shielding and grounding AT ONE END of the cable segment from the inside of the building to the lightning protector. If you ground both ends you create the problematic ground loop.
 
Proton
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Re: connectors?

Tue Feb 07, 2012 3:22 pm

thank you all for your ideas I'll try the better grounding stuff to try to eliminate all the problems with boards going bad. I'll keep everyone posted on how it works out
And how is your progress?
 
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normis
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Re: connectors?

Wed Feb 08, 2012 10:08 am

Correct use of grounding is already explained in our manual:
http://wiki.mikrotik.com/wiki/Manual:Grounding

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