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Attaching ladder line to house

Aug 7th 2011, 23:39

tuckert

Joined: Sep 28th 1999, 00:00
Total Topics: 0
Total Posts: 0
Concerning ladder line is it imperative to not have it near any metal? I need to attach at least 6 feet to the house prior to switching to coax to enter the shack and there is an aluminum gutter all along that edge of the roof. Do I use standoffs of some type, and then under the eaves must I not use metal brackets to fasten to the wooden structure of the eaves? This ladder line is not the open ladder line but a more solid looking feedline that came with the C5RV antenna I recently purchased
Aug 8th 2011, 15:08

W1MG

Joined: Apr 4th 1998, 00:00
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I use standoffs from The Wire Man for this purpose and they work great. See their Web site at www.thewireman.com for more information. I think the catalog item number is 811.
Aug 8th 2011, 23:49

tuckert

Joined: Sep 28th 1999, 00:00
Total Topics: 0
Total Posts: 0
awesome, I want to do it right Thank You!
Aug 9th 2011, 00:19

W1RFIAdmin

Joined: Jul 25th 2011, 14:25
Total Topics: 0
Total Posts: 0
Open-wire line can be very low loss. Most ladder line is a bit more lossy, but still low enough loss that you can operate it into a wide range of antenna loads and still have acceptable losses.

Ladder line does not radiate much in the far field, but very near the antenna, there is a strong electric and magnetic field very near the wires, typically within 6 inches. These fields do not radiate away from the feed line because the energy that is radiated is returned to the feed line. This is similar to what can happen an inductor or capacitor, so these fields are reactive. In fact, they are called reactive near fields.

If I had an open wire line that was going to pass about 6 inches away from some exterior metal, I would use W1MG's suggestion about standoffs. When I used EZNEC to look at a model of an open wire line with a nearby conductor, the software showed that the presence of the other conductor 6 inches away had little effect on the amount of power delivered to the load I had programmed. The balance on the line remained reasonable and the model indicated that the feed line would work well.

If you get much closer than 6 inches, though, there will be some loss due to some of the reactive near field energy coupling into the nearby conductor. This can be minimized by putting a rfew twists int the feed line, especially where it is near the gutters.

I'm not sure that I'd run 1500 watts with gutters near my feed line like that, though, and in any case, do ensure that the feed line cannot come loose and contact the gutters, as that could pose a safety hazard, for a number of reasons.

Many of us have to erect antennas that are not ideal in a number of ways. As long as the compromise is reasonable, as it would be in the case you described, if you have done the best you dan for the circumstances you are in, the antenna will almost certainly make contacts for you.

Look at it this way -- if a compromise antenna were only 10% efficient, that sounds horrible, right? Well, maybe, but if you were running 100 watts into that antenna, that would be like running 10 watts into a perfect antenna, and QRPers do it all the time!

73,
Ed Hare, W1RFI
ARRL Lab
Technical forums moderator

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