I've been involved with designing and installing communications systems for
over thirty years, are here is my take on the proper installlation and
grounding of the SmartBridge units (and WISP equipment in general)....
TOWER TOP ACCESS POINTS/BRIDGES
1. In any area that is prone to lightning, grounding and protection of
the antenna port is a must. With the units that are fed from the ground
with PoE (power over ethernet) and an antenna jack, first--screw a high
quality lightning supressor on the N-female jack on the radio--the
Polyphaser PSX-ME is what I prefer. It has a male connector to screw onto
the radio and a female for attachment of the antenna cable. Since the case
of the radio is plastic and does not ground to the tower (not really a good
idea in my opinion but we're stuck with it), use a grounding kit to securely
bond the body of the protector to the metal leg of the tower.
2. I am suspecting that many of the radio failures are due to induced emp
from nearby lightning strikes on the ethernet cable itself which is acting
as an antenna to pick up the pulse. For this reason I suggest the use of
outdoor shielded cat5--the kind with icky pick embedded in the inner layer
among the pairs, a first pvc insulation layer, an aluminum jacket with
additional icky pick and finally an outer PVC jacket. At the radio end,
terminate the connection as close as you can get it to the radio--the new
style radios I would terminate it in the weatherproof splice box. You will
need a bonding kit to attach a ground wire to the aluminuum jacket--these
are commonly made by 3M and available from Graybar. Using a #10 or larger
wire attached to the stud on the grounding kit, bond the shield to the leg
of the tower, keeping the ground wire as short as possible. The best way I
have found to do this is to assemble the grounding kit to the shield about
6" from the end of the cable where the pairs will be attached, then slide
some Panduit DB shrink with hot glue sealant inside over the splice and
shrink it down to weather seal the bond. Since you also need the ground for
the antenna protector, you can clamp a phospher bronze ground clamp to the
leg of the tower directly below the radio and attach both the ground from
the antenna protector and the cat5 ground to the same point. Graybar has
the Panduit shrink and ground clamps as well.
3. Install another bonding kit on the cat5 where it leaves the tower,
again you can seal it with Panduit DB shrink.
4. If the run up the tower is more than 150' (50M) or so, I would
probably bond the shield in the middle of the run as well.
5. Where the cat5 terminates, again bond the shield to a ground....#8 or
larger copper wire back to the tower ground is preferable, lacking that the
building ground....and make sure someone has bonded that to the tower ground
with #6 or larger copper.
6. Lastly, between the end of the shielded cat5 and the PoE injector,
install a good quality PoE surge suppressor--Motorola makes a nice one for
their Canopy products and is available from Tessco for about $40. Make sure
the ground stud on it is tied to the same ground feeding the end of the cat5
shield.
7. Code generally requires that the protector beinstalled where the cat5
enters the building, so the place to terminate the shielded cat5 and install
the Motorola cat5 protector is on the outside of the wall, and transition
there to normal cat5 in to your power injector.
ROOFTOP ACCESS POINTS/BRIDGES
1. Many times either an access point or cpe radio will be installed on
the top of a commercial building or home. The same rules apply with some
modifications because of the installation.
2. If it is a customer radio that is not as critical as an access point,
you may choose to dispense with the lightning supressor on the antenna--but
DO at the minimum bond the shield of the coax to the galvanized metal
support mast or support structure or DSS mount. One option for this would
be to loosen the lock nut for the N female connector on the radio and
install a piece of sheet metal under the nut to attach a ground wire--we've
done this and it works well.
3. You still need to use shielded cat5 and bond the shield to the common
antenna ground point as described in the previous section on tower
grounding.
4. Since the antenna support is most likely not grounded in this
instance, you need to attach a #6 copper wire to the support stucture (the
5/16 bolts securing the tripod to the mast is a good spot) and bring it down
along with the cat 5 to where things enter the building.
5. Attach the #6 wire to the ground lug on the cat5 protector, along with
the cat5 shield, then continue to the closest attachment point to the
building system ground.
INDOOR ACCESS POINTS AND BRIDGES
1. In those cases where the installation is using an indoor unit with
coax out to an outdoor antenna, I would direct you to a typical installation
of a certified SmartBridge CPE:
http://www.vircom.net/pictures/res-install/res-install.htm
2. In the case of an indoor access point, the only change I would suggest
is installation of a Polyphaser PSX instead of simply a bulkhead ground at
the entrance point.
Hope this helps a few of you out there avoid unnecessary failures.
==========================================
John Hokenson, Operations Manager
VIRCOM.NET
reply to: [EMAIL PROTECTED]
425-558-0674 bellevue
425-432-8172 king county
206-341-9421 seattle
800-806-7446 toll-free
425-432-8173 fax
WWW.VIRCOM.NET
giving you the world since 1994
==========================================
----- Original Message -----
From: "David Berndt" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Saturday, June 28, 2003 9:50 PM
Subject: [smartBridges] Grounding?!
> A bit of a mid-night rant here.
>
> I've been thinking on a lot of the failures we hear talked about here on
> the list, the quesitons about lightning, potential lightning strikes,
> lightning striking near by. Alot of the answers seem to be a combination
of
> finger crossing and some black magic.
>
> So what I'd like to see to rectify some of these issues is smartbridge
> publish a document about proper grounding. Where do we need grounds/surge
> protectors/lightning arrestors, the differences between them, etc.
>
> I know these things are all dictated by the local building code and the
> like wherever you happen to be using the product. But how about some sort
> of a document that is intended as a bare minimum/recommended practices
> document to get all the installs to be put together in a fairly similar
way
> and help correct some of the new newbie mistakes and take a bit of the
> black magic out of this.
>
> This could be a fairly simple diagram of a few different sample setups of
> the outdoor equipment. I am especially interested in the total equipment,
> is there a polyphaser in there? Should the cat5 be grounded when using
> sheilded cat5, otherwise? Surge protector on the cat5? before/after the
POE
> device? etc etc.
>
> A recommended parts list wouldnt be horrible either. I do not want to see
> this enforced, but more documentation and standardization would make
things
> clearer for everyone, provide a quick way to answer peoples questions and
> maybe make everyones systems a bit more stable.
>
> Hope that made some degree of sense.
>
> Dave
>
> The PART-15.ORG smartBridges Discussion List
> To Join: mailto:[EMAIL PROTECTED] (in the body type subscribe
smartBridges <yournickname>
> To Remove: mailto:[EMAIL PROTECTED] (in the body type unsubscribe
smartBridges)
> Archives: http://archives.part-15.org
The PART-15.ORG smartBridges Discussion List
To Join: mailto:[EMAIL PROTECTED] (in the body type subscribe smartBridges
<yournickname>
To Remove: mailto:[EMAIL PROTECTED] (in the body type unsubscribe smartBridges)
Archives: http://archives.part-15.org
