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Author Topic: Feedline bulkheads  (Read 3004 times)

Posts: 199

« on: August 24, 2003, 05:28:59 PM »

Any ideas for construction of a coax feedline bulkhead?  I want to build a means to gather together all my coax feeds at my house and be able to switch them to ground from outside.  Kind of like switching the house AC from the mains to a generator, for instance.


Posts: 21837

« Reply #1 on: August 25, 2003, 12:07:32 PM »

You can buy such items already made for the purpose from Poly Phaser and others.  They're not expensive, and might be a better deal than homebrewing.

Otherwise, of course you could just mount rotary coaxial switches (the type that can "ground all ports" in one position) outside on a metal bulkhead panel, and run the switch shafts through the panel so the knob can be reached from inside.  When you want to ground everything, turn the knob to the grounding position and you're done!  Of course, this still isn't quite as nice as completely disconnecting all the lines, and you might still have to think about isolating rotor cables and other lines that are not coaxial...



Posts: 1

« Reply #2 on: August 26, 2003, 01:54:46 AM »

Question: Why do you want this outside switching bulkhead? Lightning protection research theory and partical application have both brought contidiction to the problem.
What is your goal in this project? Your location, antenna field area and height, feed line size, etc, all became a factor.
After many years of study, conversations with victims, forums on static and RF problems, personnal experence; we hams are at a no win statis.
Simply, we cannot protect against any direct lighting strike, be it to any antennas, power company lines, Phone lines, or a ground strike near our site. To many amps of uncontrolled electricity will have an effect on something in your site. I personnally had a Phone line hit that took out phones, answer machines and modems/computer parts in the 80's.
A friend, K0UBA, lost most of his station thru a ground strike near his inter city home. 1995
Others have had coax failure at right angle turns of any size coax or hard line, (lighting doesn't turn corners well). 1992
Insuraance is a good idea, but read the fine print. What is covered, what is not. The cost per unit per day, per replacement cost.
I will indource your "outside disconnect" as a good idea, but it depends on the size, eaze, method and distance of disconnect. Lightning can jump miles, so a switch in the line is wasted.
For local protection info, go to your local AM and FM Radio station Engineers (most likly Hams hiding out in paying jobs). If you can afford what they pay for lighting protection that is not prefect, and will cost them someday, pay it.
If not? Play the Risk game. If you play the lotory it's the same as buying new ham gear without  a warrenty.
Final answer: Nothing promised, 600,000 hams that have won and lost accordingly.

I know I dragged this out, but we cannot stop Mother natures actions. Protect what you can, anyway you can, at the price you can afford, when you can.  
Questions will be answered for all inquiries.

Posts: 199

« Reply #3 on: September 20, 2003, 04:16:15 PM »

Thanks WB2WIK for your suggestions.  I thought about the ol' disconnecting the feeds from the rigs routine, but doesn't that still create the potential for arcing?  I realize there's no way to avoid a direct lightning hit.  All I want to do is somehow "frustrate" the possibility the best I can.  How is your shack set up for the possibility of lightning strikes?

Thanks again,
Tom, N8EUI

Posts: 161

« Reply #4 on: September 21, 2003, 01:11:47 AM »

I don't know what Steve does (except that I'm certain it's safe and makes sense), but there's a school of thought that believes in attaching female coax connectors to a ground rod and hooking up feedlines there when they're not connected to a rig. That would be one example of "completely disconnected" that avoids the danger of arcing.

You're quite right, by the way, about the possibility of lightning flowing through a disconnected feedline.

Posts: 2415

« Reply #5 on: October 06, 2003, 01:59:40 AM »

Read and follow the good advice on the Polyphaser Tech.
notes website regarding lightning protection:
I take DIRECT lighting hits most every big lightning
storm. With no damage. So do most all commercial
radio stations, Police, Fire, Ambulance, etc. towers.
NONE of these stations "disconnects" coax when a storm
approaches.  And all of them that are properly grounded
do not suffer damage from direct hits.
A homemade bulkhead could be made up using copper or
aluminum, But as long as you follow the single point
ground theory you should be OK. (Just attach all
coax switches, Lightning arrestors, etc. to a large
copper or aluminum sheet near where your coax enters
the shack. (A four inch clothes dryer vent makes a
great entry port)
The only problem using aluminum instead of copper is
when you get outdoors. Copper is the only product to
use where it comes in contact with the soil. Most all
soils will "eat" aluminum.  You can sometimes get copper sheet from upscale roofing companies.
Use "hard" silver solder to bond together.

Posts: 199

« Reply #6 on: October 14, 2003, 01:09:39 PM »

Thank you for all your suggestions.
Tom, N8EUI
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