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Author Topic: Stand Off for feed line  (Read 2681 times)
K0UIF
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Posts: 3




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« on: July 20, 2012, 08:16:08 PM »

I feed an Inv-V with a 600 ohm twin line running up a metal pole (not tower).   

  Cable ties (UV resistant) held the standoffs to the metal pole and also held onto the feed line. Over the last 2 years UV and wind have destroyed the cable ties.

I am looking to fabricate standoffs with PVC or something. 

Question:  Do I need to hold the feedline to the standoff posts with something NON-Metal or can I use metal ties?  Would it make a difference?

Also, would appreciate any other advice!

Thanks all
Dan....k0uif
 
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K0ZN
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Posts: 1553




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« Reply #1 on: July 20, 2012, 10:09:21 PM »

Good question...... in the perfect world, you do not want "other conductors" around or near parallel line.  But... on the other hand, a SMALL....like, very small...
piece of wire as a tie down is a tiny percentage of a wave length at HF and would have only microscopic amounts of C and L as it relates to the line.  
If you are going to do that, I would suggest separate, VERY short pieces of wire around each conductor, thus not "disturbing" the field between the wires.  
Worst case would be a wire across/around the line as it would theoretically increase coupling.  

There must be some GOOD tie wraps that really are UV resistant out there....... that would be my first choice.....

It will be interesting to see what other's say or suggest.

73,  K0ZN
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KC4MOP
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Posts: 743




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« Reply #2 on: July 21, 2012, 04:38:49 AM »

OK how's about UV resistant (black?) PVC 1 inch dia. about 1 foot long. (I made 2 feet long to support a wire antenna for another band, to reduce coupling.)
Drill a hole big enough for a stainless steel hose clamp to go through and attach to the tower leg. Using care and a hacksaw blade, cut a little V out at the bottom to give a little attaching surface on your metal pole.
There are a large assortment of SS hose clamps in the home improvement stores to select the size you need to attach the PVC to a tower leg or your pole.
At the top of the PVC drill another hole to allow a UV resistant ty-wrap to attach to the center support of the ladder line.
I assume that 600 ohm ladder line is 6 inch spaced? There will be plastic or wood dowels to maintain the distance along the transmission line.
I got a little confused when you mention twin lead. I hope you're not using 450 ohm window line. Tuning shifts in the weather.
Either way, the method I used will allow for a UV protected Ty-Wrap to clamp onto the window line, enough so as to not distort the shape of the window line.
Fred
« Last Edit: July 21, 2012, 05:13:54 AM by KC4MOP » Logged
W5DXP
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Posts: 3613


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« Reply #3 on: July 21, 2012, 01:52:27 PM »

I am looking to fabricate standoffs with PVC or something.

Before you do that, take a look at the electric fence standoffs at your local farm and ranch supply store (or even Lowe's). Here are just a few.

http://www.electric-fence.com/category_48/T-Post-Insulators.htm

Some of these insulators are ideal for ladder-line.
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
KC4MOP
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Posts: 743




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« Reply #4 on: July 22, 2012, 05:55:28 PM »

The T POST insulator looks nice but the price is ouch!!
We'll have to figure that the op's pole might be 30 feet and he would need at least 5 points to keep the OWL away from the pole.
Some PVC 1 inch pipe about 2 feet long for 5 locations would be a lot cheaper. A little more innovation needed for the PVC and some SS hose clamps and you're done.

Fred
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W5DXP
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« Reply #5 on: July 22, 2012, 08:29:17 PM »

The T POST insulator looks nice but the price is ouch!!

They are much less expensive at your local farm and ranch supply store.
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
WB6BYU
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Posts: 13334




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« Reply #6 on: July 22, 2012, 09:57:42 PM »

Quote from: KC4MOP

The T POST insulator looks nice but the price is ouch!!
We'll have to figure that the op's pole might be 30 feet and he would need at least 5 points to keep the OWL away from the pole.



No rancher would pay that much per insulator for mile of fence.

If you follow the links for any one product you'll see that the quoted price is
typically for a bag of 25 insulators.

If they will do the job, it is hardly worthwhile making your own.
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KC4MOP
Member

Posts: 743




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« Reply #7 on: July 23, 2012, 04:02:35 AM »

Quote from: KC4MOP

The T POST insulator looks nice but the price is ouch!!
We'll have to figure that the op's pole might be 30 feet and he would need at least 5 points to keep the OWL away from the pole.



No rancher would pay that much per insulator for mile of fence.

If you follow the links for any one product you'll see that the quoted price is
typically for a bag of 25 insulators.

If they will do the job, it is hardly worthwhile making your own.
Not a bad deal after all. Bag of 25

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