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Author Topic: Feedline Options - 370' run  (Read 1861 times)
KA3TKZ
Member

Posts: 8




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« Reply #15 on: January 09, 2009, 05:24:58 PM »

Darin,

I made the same run.  I used VXL5-50 which is a more flexible LDF5-50, both are Heliax.  The connectors were about $30 apiece.  I made the run directly from the station to the antenna switch 90 feet into the air.  I used 2 1/2 inch grey electrical bury conduit.  I ran my cables ( coax, rotator, antenna switch ) in the conduit and sealed both ends and purged with nitrogen.  I then pressurized the conduit to 5 PSI nitrogen.  This is a bit of overkill.  I would not run a separate ground as it sounds like your tower is pretty far from the shack.  I used grounds at the tower and I also put in some radials for a grounds so I can feed the tower for 160 meters. I only burried mine about 6 inches.  Have fun with the setup.


Whitney
N3ZV
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WG5J
Member

Posts: 21




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« Reply #16 on: January 09, 2009, 07:30:51 PM »

All good input.

What about RG-6 for beverages?  

D.
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K9KJM
Member

Posts: 2416




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« Reply #17 on: January 10, 2009, 02:29:03 AM »

QUOTE:  "I would not run a separate ground as it sounds like your tower is pretty far from the shack."

BAD, BAD advice!    THINK about it.   You are ALREADY grounding the tower to your hamshack via the coax shield!!!!!!!!

It is MUCH safer to run a bare copper ground wire outside your conduit for extra lightning ground!

See:  http://members.cox.net/pc-usa/station/ground3.htm

Several runs of RG-6, RG-11, And maybe even a few of surplus CATV "hardline" would be a good idea.

Check with your local friendly cable TV installer for a good deal on "spool ends"  Usually available for a bag of donuts..........
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KB1NXE
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Posts: 299




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« Reply #18 on: February 05, 2009, 11:38:47 AM »

Maybe not bad advise.  Read the following tech notes and see how they may apply:

http://www.polyphaser.com/technical_notes.aspx

There may be a better way and that is to use metal conduit from tower to shack.  Bonded at both ends to the ground.  This conduit will become part of the ground and act as a Faraday Shield to the cables it contains.

Documents in the above tech notes will discuss the issue of magnetic coupling from a near strike (could be the tower or a nearby tree) into the cables.  You also need to look at the inductance the buried cables will have and use it to calculate the entire circuit.  What you need to do is place a conductor that offers a lower inductance than presented by the coax.  This way it will take most of the current presented by the lightening.  Depending upon the numbers and size of coax used, that conductor may be something larger than 1/0 copper wire!

Proper grounding is not a set of hard and fast rule as each situation is unique.  Best to ask someone who knows what they are doing rather than invite trouble into the house.

I recommend all users of antennas be familiar with the notes in the above link.  PolyPhaser is basically giving away hundreds of dollars worth of grounding and lightening protection training for free.
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WG5J
Member

Posts: 21




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« Reply #19 on: February 05, 2009, 12:39:33 PM »

There is a wealth of info there - I have read every one of them.  Of course one has to balance the cost of a ham vs. commercial installation and weigh the risks.  

I will be using lightning arrestors on the tower.  
Copper strap and ground rods and and extending from the base.  
All cables under ground
#6 copper wire in trench with ground rods along the way.
Common ground at cable entrance to shack with grounding bar for rig, etc.

I have lived with worse.  We will see how things survive.

D.
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WB7TXG
Member

Posts: 21




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« Reply #20 on: February 22, 2009, 05:31:21 PM »

I'm running Davis RF Bury Flex in the ground out to my tower. The run of coax is about 250 feet.

Specs are advertised at 2.9 db loss at 400 mhz.. I also have a single control ine running out to my ameritron 5 position remote antenna relay box.

The coax has been in the ground (direct buried) with no pvc pipe, etc for 7 years now.

I seem to be able to work what I want when I want. Hard line is probably a better alternative but at the time bury flex is what I could afford.

If I get another 3 years out of the coax and have to replace it then.. well.. that's a fair trade for 10 years and $125 investment in coax.

If I need to replace the coax I will simply lay another run to the tower, use my spade and gently slit the sod and put in another run.. The old one can stay there..

Oh.. I use telephone cable that I got at a surplus sale for the control line out to the siwtch box..

I don't like the idea of having the coax "elevated" out to the tower. There is a chance of some unwanted feedline radiation and perhaps some unwanted RFI.. With the coax in the ground I feel this minimizes potential RFI issues with the neighbors..


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