Rob,
Each installation has different circumstances that can be solved in
different ways. One of the biggest obstacles I see with a great number
of hams is they do not really understand what single point grounding
means. If you put some time into really understanding what is going on
with that concept you are way ahead of the game no matter what the
budget is. Just the way things are plugged in at the shack can make a
big difference.
For example, it is not necessary to have the mains power coming in the
same place as the coax lines. Just run a power line from a convenient
place over the where you have your antenna entrance panel. Put your
power line protectors there. Now run ALL your shack equipment from that
one power point.
The protectors for the power can be as little as some large mov's that
will give some protection. Add some gas tubes of the appropriate type.
If you want to go a little farther add some series inductors in the
power line ahead of the mov's and gas tubes.
Look at what is in some of these protection devices. It isn't magic it
is just proper selection of components.
As far as Polyphaser protection devices go, you really don't need them
if you disconnect the lines from the equipment and ground the shield and
center conductor of the coax when not in use.
A polyphaser device is a convenient way to ground the shield of the coax
line at your entrance point. You can do the same thing with a clamp
around the cable or connector, or plugging the connector into a mating
connector that is fastened to your ground.
The only other thing that the protection device does for you is shunt
any lightning energy on the center conductor of the coax to ground when
you don't have it removed from the rig and connected to ground.
It is more important to connect grounds in the right place than it is to
have elaborate ground systems.
73
Gary K4FMX
Rob Atkinson, K5UJ wrote:
> this whole topic/conversation shows a pretty good reason to have
> professionals install subpanels.
>
> All the advice, recommendations involving SPG and so on sound great and i
> won't argue with them as they are correct, but whenever professionals start
> advising hams on grounding, protection, and so on, they often overlook one
> major thing--hams usually have stations in homes. Homes are almost never
> constructed to be telecommunications sites. So all the wonderful advice
> the professional is giving, where in his mind, he is picturing cable trays,
> backhoes and ditch witches digging trenches everywhere, with gravel all over
> the ground and the power company coming in with a bucket and three hard hats
> to put the 3-phase line just where you want it--and when he's done talking
> the ham says thanks and goes home and unplugs everything and that's the end
> of that. I mean, i'd like a little more realistic advice for some guy in a
> house who can't move the service drop around back where the tower is, and
> can't dig a 4' deep trench all the way around the house and cadweld
> everything to a 4" strap.
>
> costs: i once added up the cost of all the polyphasor stuff to do the job
> right and came up with around $2K. This is nothing for a guy with $20K in
> this hobby, but some guy with 2 grand in it will probably balk at that.
> why do hams not spend the money on gas discharge devices and all the other
> gear? there's a cost/fun price point somewhere in there where a lot of us
> make spending decisions that aren't always logical or rational--we'd rather
> blow our money on the fun stuff and take our chances, because that's what a
> hobby is about, having fun. I'm not saying that's always okay; i'm just
> saying that's how it is.
>
> one final comment: an all out professional protection job doesn't guarantee
> you will always be protected--if you don't believe me ask a broadcast
> station CE. i know of one A1 station near me that took a direct hit on
> their 190 degree tower (probably a positive strike) and lost their nice,
> fairly new s.s. tx--had to get a new one.
>
> rob/k5uj
>
> <<<Can you really HAVE a single point ground? Even if the RF and power
> service
> entrances were immediately adjacent, and tied together with 3" strap...the
> drop circuits from each will follow different paths, and may have induced
> current on them from the primary strike...with different potentials due to
> their geometries. I still disconnect everything in the main shack.
>
> In a 24/7 broadcast installation, or amateur repeater, you clearly can't do
> that. You take reasonable precautions, and hope for the best.>>>
>
> _________________________________________________________________
> Express yourself instantly with MSN Messenger! Download today - it's FREE!
> http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/
>
> _______________________________________________
>
> 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.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|