There are two (three if you count the one on this list) schools of thought
on this.....
1. Only ground one end so you don't get a ground loop
2. Ground both ends so it does not act like an antenna
3. Don't ground it at all and just let the induced voltage rise and
fall on the shield.
Since I was asked, by take on this is to treat it as if it were a chunk of
coax....you have internal conductors and a jacket. Polyphaser has a nice
treatese on what happens during a lightning strike....been a while since
I've read it but the gist of it is this--When a strike occurs, the current
flows between the point of contact and the point of lowest potential.
Really does not matter whether it's a streamer coming off the tower upwards
or whatever. The point is, you have induced current flowing down the steel
(or up, whatever) of the tower, the copper or alumunum jacket of the
feedline and the center conductor. Well, in coax there is something called
VELOCITY FACTOR, as well as the inherent inductance of the long chunk of
wire that is the center conductor. What it means to you is that as current
flows down the shield and the center conductor, THEY FLOW AT DIFFERENT
RATES. The net effect of this is that by the time they get to the end there
is a potential difference (IE voltage) between the shield and the center.
What concerns me is that if the cat5 is actiing like a coaxial conductor
(which it will) you can end up with a considerable potential there. That's
why I do not want the shield to rise above the potential induced on the
tower and I ground both ends. Make sense?
JH
----- Original Message -----
From: "Jerry Carter" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Thursday, July 17, 2003 11:28 PM
Subject: Re: Re[4]: [smartBridges] New Firmware
> Hey John,
> One question, Do you ground the shielded ethernet at the top by the
> radio or on the ground? I just installed a setup with it and grounded it
at
> the bottom (ground). Did I make a mistake?
>
> Jerry
>
> ----- Original Message -----
> From: "John Hokenson" <[EMAIL PROTECTED]>
> To: <[EMAIL PROTECTED]>
> Sent: Friday, July 18, 2003 1:22 AM
> Subject: Re: Re[4]: [smartBridges] New Firmware
>
>
> > A couple of suggestions to make things happier up on top of the
tower....
> > 1. Use the Polyphaser that has a male on the equipment side
and
> > female on the antenna side and screw it directly on the SB AP.
> > 2. Bond a good ground connection from the Polyphaser to the
> tower
> > leg--#10 or larger wire--you can order a flat plate from Polyphaser that
> > attaches under the provided locknut to give you two screw holes to
attach
> a
> > double hole crimp lug to it.
> > 3. Run DB style shielded Cat5 up the tower and bond the
shield
> to
> > the tower at the top, 150' down (middle) and at the bottom where it
leaves
> > the tower.
> > 4. If you are using the maxrad 120* sectors, save yourself
some
> > grief and a. Throw away the lousy tilt mounts they provide...they are
> > aluminum and to not stay in place....we picked up some stainless conduit
> > hangers and stainless 1/4-20 hex bolts and attached them directly to the
> > tower leg, using some spacers on the top hanger to get exactly the
correct
> > amount of downtilt we wanted.
> > 5. Also, make sure you order them with a male N connector so
it
> > will attach directly to the female on the Polyphaser.
> > 6. Lastly, seriously consider putting the antenna, Polyphaser
> and
> > radio together on the ground--and using 3:1 DB shrink (the kind with hot
> > glue on the inside) to seal the antenna-to-polyphaser and
> > polyphaser-to-radio connections--you'll be glad you did. Alernatively,
I
> > would rather use Scotch self-fusing rubber tape and Scotchkote than
rubber
> > tape. When I use this technique I put 4-5 layers of rubber tape that
> fuses
> > into a single piece, then three coats of Scotchkote---been doing this
over
> > 30 years now and never had it leak.
> >
> > JH
> >
> > PS...you might want to search the archives for my treatese on proper
> install
> > techniques.
> >
> > PPS...YDI has a nice calculator for setting the downtilt.
> > ----- Original Message -----
> > From: "Tom Haynes" <[EMAIL PROTECTED]>
> > To: <[EMAIL PROTECTED]>
> > Sent: Thursday, July 17, 2003 10:39 PM
> > Subject: RE: Re[4]: [smartBridges] New Firmware
> >
> >
> > > You will need 6 coaxial jumpers (one on each side of the polyphaser)
> > unless
> > > you use the Nfemale-Nmale protector. Add in 6 rolls of 3m 33
Electrical
> > tape
> > > ($2.50ea) as well as a can of 3m liquid electrical tape ($10-20).
Don't
> > > skimp on the weatherproofing! You will need an enclosure at the base
of
> > the
> > > tower (unless there is a building) to put the power supplies, router,
> > > powerShot, etc... .
> > >
> > > -----Original Message-----
> > > From: [EMAIL PROTECTED]
> > [mailto:[EMAIL PROTECTED]
> > > On Behalf Of [EMAIL PROTECTED]
> > > Sent: Friday, July 18, 2003 12:33 AM
> > > To: Bill Flood
> > > Subject: Re[4]: [smartBridges] New Firmware
> > >
> > >
> > > On Fri, 18 Jul 2003, Lancaster Networks wrote:
> > > > I need to provide them with a COMPLETE proposal of this whole thing,
> > > > and right now, this is what I am going to propose to them:
> > > >
> > > > (3) SmartBridges AirPoint Pro Outdoor @ $330.00 ea = $990.00
> > > > (3) Maxrad 120 degree beamwidth antenna @ $407.52 ea = $1222.56
> > > > (3) LMR-400 4ft jumper coax cable @ $24.00 ea = $72.00
> > > > (3) Polyphaser 2.4ghz coaxial lightning protectors @ $35.66 ea =
> > > > $106.98
> > >
> > > Looks good.
> > >
> > > > Has anyone needed to use polyphasers? We use them as a standard
where
> > > > you have 100-300 foot hardline runs, but in this case, it's ethernet
> > > > cable. But I don't feel like climbing up the 300 foot tower to
replace
> > > > a blown radio either.
> > >
> > > Polyphasers rock. But you know this already. Put a Coax protector on
the
> N
> > > connector at the radio, and run your antennas pigtail off of that. Be
> sure
> > > to ground the polyphaser well. The SmartBridges use a plastic case, so
> you
> > > can't ground em. Once the ethernet comes inside, put a Polyphaser
IS-T1
> > > protector on the ethernet. They make a three port model, would be
> perfect
> > > for you. Bear in mind you will need to protect the PoE seperately. The
> > IS-T1
> > > only protects two pairs. (Or 2 pairs X 3 ports on the IS-3T1)
> > >
> > > > This brings me to another point, are SB's products reliable enough
> > > > that I won't need to spend my entire life climbing the tower to fix
> > > > them or reflash them? them?
> > >
> > > There are no serial ports on the units, and you can reset the
> > configuration
> > > from the power injector, so I don't see why you would need to climb,
> > except
> > > to replace the entire radio. My APs are all Cisco or Trango, never
used
> > > SmartBridges anywhere other than a CPE. Not sure if I would trust
them.
> > >
> > > > I plan on mounting the antenna's with a bit of a downtilt, but all
at
> > > > the top of the 300' tower, because I am looking for long-range
> > > > performance. Any methods for calculating downtilt that work good?
I've
> > > > used my knowledge in the broadcast/radio industry to make my own
> > > > calculations, and with the use of ComStudy (an excellent program for
> > > > calculating RF propagation)
> > >
> > > YDI (www.ydi.com) has a number of javascript forms that will do all
the
> > > common calculations for you. Check em out.
> > >
> > > Jeremy
> > > (Fromer Lancasterite)
> > >
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