If you look at the lightning suppressers as a device to equalize the
potential between the shield and center conductor of the coax then maybe
it will be easier.
Also look at the ground connection on the suppression device as a
convenient way to ground the shield of the coax.
In other words, the lightning suppression device is not the "stop all
device for lightning and nothing goes past it".
Just a note on the operation of the protection devices. The capacitor on
the equipment side is necessary in order for the gas tube to fire before
the equipment burns up. Most radios have a coil from antenna connector
to ground. If there was no capacitor in series the lightning voltage
would have to burn open the coil in the receiver in order to rise high
enough to fire the gas tube. The capacitor allows the voltage to rise
without forcing the voltage across the receiver coil to also rise.
Those protectors without a series capacitor are of little value in those
instances. Unless your receiver has a series capacitor already.
A shunt inductor on the antenna side also will not allow the gas tube to
fire unless the inductor is first burned open. A resistor at that point
would work ok.
By not having the protection devices at the shack entrance you really
don't have a single point ground system that you may think you have.
The ground at the tower is too far away. You also need a good ground
system at the shack entrance, where the protectors should be.
On one side of the protection devices are antenna and ground
connections. On the other side should be only your equipment with no
long runs near grounds or other conductors that can conduct lightning
energy. It is important to keep the two sides of the protection devices
isolated from each other physically.
You want all your equipment grounds, power and antenna cable shields and
center conductor grounds at one spot and that spot connected to a good
short ground system.
Energy can be induced on to and into the cable between the tower and the
shack even though it may be well grounded at the tower. And it can also
again get into the center conductor of the coax in the run to the shack.
It may seem like it won't because it is coax but it can get there the
same way it got there on the other end. Even with grounded antennas,
(that is a short between coax shield and center conductor at the top of
the tower), lightning energy makes it's way to the center conductor. It
happens by what is called "transfer impedance".
73
Gary K4FMX
Gene Smar wrote:
> TT:
>
> Polyphaser and ICE and other types of lightning suppressors shunt to
> ground the lightning energy that is injected onto the center conductor of
> the coax. Let's all agree on that point. How they do it (provide the
> shunting effect) varies with the design of the device.
>
> Polyphasers have a series DC blocking cap, and a shunt gas discharge
> tube on the antenna side of this cap (
> http://www.arraysolutions.com/Products/ice/33.htm ). ICE devices (also at
> this URL), in addition to the cap and tube, have a shunt inductor at the
> antenna connector (to bleed off slowly-building charges) and a shunt
> resistor on the equipment side of the device. Alpha Delta devices (
> http://www.arraysolutions.com/Products/ice/33a.htm ) have a shunt tube but
> no series cap. ALL of these devices are designed to shunt lightning enrgy
> from the center conductor to ground, as I said above. *
>
> In my tower system, I installed Polyphaser devices in a steel, grounded
> box at the tower base. I chose this location because the ground system at
> my tower consists of three ground leads welded to a dozen ground rods,
> providing (I hope) a fairly low impedance to ground for lightning energy. I
> could have installed the Polyphasers at the shack entrance along with my SPG
> panel as is being suggested by some below. However, at this location I have
> only ONE ground lead to ONE ground rod (This rod is actually the last rod,
> farthest from the tower, in my tower ground field system.) In my
> estimation, the tower location provides a much lower impedance connection to
> ground (three leads and many rods) as compared with the shack end (only one
> rod and 50 feet of wire to the tower's ground field.) I wanted to dump the
> lightning energy from the Polyphasers into a better ground connection - at
> the tower. Also, this connection was farther away from my house than the
> SPG connection outside the shack. (First Rule of Lightning Protection: Keep
> the strike energy away from your shack interior.)
>
> My conclusion is that, given a choice, one should connect lightning
> suppressors 1. to the better (lower impedance) ground point and 2. farther
> away from the shack. The recommendation to install such suppressors outside
> the shack, in my opinion, is not a good idea unless the tower is also just
> outside the shack. In this case the lowest impedance connection to the
> ground system is most likely at the tower/outside the shack. In my case,
> the tower is fifty feet away.
>
> BTW - Knowing what I now know about the design of various suppressors
> (above), I probably would have selected ICE devices. But they don't come in
> a bulkhead mount design, only a flange design. They are not able to be
> poked through the sides of the steel box I have. One can only hope.
>
>
> 73 de
> Gene Smar AD3F
> * I realize that this information is found on the web pages of one of the
> competing vendors - ICE. Caveat Amateur.
>
>
> ----- Original Message -----
> From: "Gary Schafer" <garyschafer@comcast.net>
> To: <dickgreen@verizon.net>
> Cc: <towertalk@contesting.com>; "'Craig Sande'" <ae7i@yahoo.com>; "'Craig
> Lekutis'" <craiglekutis@wirelessestimator.com>; "'Gene Smar'"
> <ersmar@comcast.net>
> Sent: Saturday, April 02, 2005 2:09 PM
> Subject: Re: [TowerTalk] Wet setting conduit?
>
>
>
>>While it doesn't hurt to put protection devices at the tower it really
>>doesn't do too much good. Keep in mind that lightning energy on the
>>center conductor of coax has already made it all the way down the tower
>>in the coax. If it hasn't arced over by that time it will probably not
>>by the time it gets to the shack.
>>
>>The whole purpose of the protection device is to equalize voltages on
>>all conductors at one place. You always want protectors at the shack
>>where everything is tied together (single point ground).
>>
>>Yes grounding the shields to the base of the tower is recommended.
>>
>>Just so some don't get confused about "grounding to a single point at
>>the shack". That doesn't mean that you have an elaborate ground system
>>at the tower base and then only one ground rod or connection at the
>>shack end. The shack end where the single point ground system is also
>>needs an elaborate ground system of its own if it is located any
>>distance from the tower ground system. It should also be connected to
>>the tower ground system.
>>
>>73
>>Gary K4FMX
>>
>>Dick Green wrote:
>>
>>>Not necessarily. According to the ARRL Handbook (or maybe it's the
>>
> Antenna
>
>>>Book) and Polyphaser, the optimum configuration is to install lightning
>>>suppressors at *both* ends -- at the tower and at the entry to the
>>
> house. I
>
>>>believe the main idea is to protect the coax run between the house and
>>>tower, which is an important consideration if it's expensive hardline
>>
> and/or
>
>>>buried in such a way that it would be hard to replace. I would think
>>
> it's
>
>>>also good to have two sets of shunts to ground in case the suppressors
>>
> at
>
>>>the tower get overloaded or fail. The shields should be grounded at both
>>>ends as well -- at the tower end to a system of ground rods and radials
>>>connected to the tower and at the house end to the single-point ground.
>>>
>>>73, Dick WC1M
>>>
>>>
>>>
>>>>-----Original Message-----
>>>>From: Gary Schafer [mailto:garyschafer@comcast.net]
>>>>Sent: Thursday, March 31, 2005 10:14 PM
>>>>To: Craig Sande
>>>>Cc: towertalk@contesting.com; Craig Lekutis; 'Gene Smar'
>>>>Subject: Re: [TowerTalk] Wet setting conduit?
>>>>
>>>>
>>>>Your lightning protection devices should go at the house not at the
>>>>tower. Ground the shields at the base of the tower though.
>>>>
>>>>73
>>>>Gary K4FMX
>>>>
>>>>
>>>>Craig Sande wrote:
>>>>
>>>>
>>>>>I finally decided not to risk any compromise to the base by
>>>>>introducing
>>>>>a total of 5 conduits. The pour will proceed tomorrow
>>>>
>>>>morning per the
>>>>
>>>>
>>>>>original engineering. When the dust settles, I will take my time
>>>>>installing the conduit runs to the edge of the pier. I'll
>>>>
>>>>probably use
>>>>
>>>>
>>>>>a NEMA box mounted nearby for the lightning arrestor
>>>>
>>>>devices and have
>>>>
>>>>
>>>>>the conduit enter directly from below. I'll run a 6"
>>>>
>>>>copper strap from
>>>>
>>>>
>>>>>the NEMA box to the tower. I'll be sure to snap plenty of
>>>>
>>>>pictures and
>>>>
>>>>
>>>>>share my experience when complete.
>>>>>
>>>>>Regards,
>>>>>
>>>>>Craig, AE7I
>>>>>
>>>>>
>>>>>Craig Lekutis <craiglekutis@wirelessestimator.com> wrote:
>>>>>
>>>>> Craig,
>>>>>
>>>>> If it's a slab foundation and the PVC entries are not near the
>>>>> anchor bolts then it might not be a problem since the
>>>>
>>>>foundation is
>>>>
>>>>
>>>>> probably designed for its compressive load and its overturning
>>>>> moment. However, if it's a pier type design, it may be a problem
>>>>> since it could affect interaction with the shaft and
>>>>
>>>>anchor bolts.
>>>>
>>>>
>>>>> Best practice is to do what you are going to do, check with your
>>>>> engineer. You'll find addition information about
>>>>
>>>>foundation design
>>>>
>>>>
>>>>> at http://www.wirelessestimator.com
>>>>> <http://www.wirelessestimator.com/> .
>>>>>
>>>>> Best regards,
>>>>>
>>>>> Craig
>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>
>>>
>>
>>
>>_______________________________________________
>>
>>See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
>
> Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
> questions and ask for Sherman, W2FLA.
>
>>_______________________________________________
>>TowerTalk mailing list
>>TowerTalk@contesting.com
>>http://lists.contesting.com/mailman/listinfo/towertalk
>
>
>
>
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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