Parallel Transmission line

[ke7trp]

Read the open wire line thread by KC6MCW.  There is a ton of info on that thread.   ALOT of BS also. So you have to weed through it.   

C

[K1JJ]

Hi Jack,

Yes, large diameter wire also applies to the flat top cuz the flat top will see basically the same current maximas and minimas as the feedline, depending on its length and the length of feedline for a particular freq. But just assume this to be so.  You want a strong flat top anyway. We always start at a voltage maxima at the end insulators of the dipole flat top and work our way back with a current maxima 1/4 wavelength from the end insulator and so forth down the feedline.

The only advantage I can see for solid wire on HF is it is less prone to deterioration when exposed. I've seen a solid single strand of #8 last for 30 years. But the thin stranded stuff will break down quicker, simply cuz of its diameter. If a single large solid strand gets corroded 1mm, it's no big deal. If a tiny strand gets 1mm, then its a problem when all the bundle gets it, strengthwise.  But for HF, I can't see any diff in skin effect. I use stranded #10 for all my wire antennnas for years. I use the inexpensive stuff from Home Despot on 500' rolls with insulation.

As for optimum length for 80-20M... it is all about antenna pattern. The best pattern to maintain is a figure eight on all three bands - that would be about 90'.   But if you put up a standard 130' long dipole, it would have a standard figure 8 on 75M, a sharp figure eight on 40M with 2db gain, but on 20M a cloverleaf with a sharp null broadside. The 20M is the problem.

I would put up a 180' flat top and use it for 160-40M as a great figure 8 antenna. Then stick up a small coax fed dipole for 20M for a nice figure 8. That wud be a good solution. An alternative would be an open wire fed 22' long flattop that wud make a figure 8 on 10M-20M.

T

[W2VW]

I am going to take down my 80 meter steel fence wire dipole and replace it with aluminum fence wire.

Do you have an ex wife in the copper wire business?

[K9ACT]

I am going to take down my 80 meter steel fence wire dipole and replace it with aluminum fence wire.

Do you have an ex wife in the copper wire business?

Funny but I just completed some extensive tests comparing steel, stranded copper and aluminum on a 160 meter dipole, both using MMAMA modeling and real antennae.

I concluded that any advantage copper has is more than offset by the lighter weight of the aluminum.

This applies to an end supported dipole.  If it can be supported in the middle at the same height as the ends, then copper has nominal advantages.



js

[K5UJ]

I will be interested in hearing how aluminum holds up.  I have always heard it doesn't do well as antenna wire -- wind movement introduces metal fatigue and breakage and/or it snaps under icing.  I know big stranded aluminum is used for service drops from pole pigs but those are usually not long spans or are large gauge.  The other prob. is the hassle of making the metal transition from Al to Cu and soldering.  You can crimp maybe but you have to work out an aluminum brass copper transition somewhere I would think.

[N3DRB The Derb]

The antenna v2.0 I made with hard drawn copper is about half the weight of the one I had up using insulated THHN. both #14. That insulation adds a lot of weight. I'll stick with HD copper, the copperweld stuff is too hard for me to work with. I dont believe in aluminum for antenna wires - for tubing it works quite nicely. 

damn pulleys still not here yet.   I cant proceed until they get here.

[W2VW]

FWIW I had 124' centerfed #8 THHN supported only at the ends for 3 years in a very windy location using wimpy trees.

It took a hell of a beating.

[N3DRB The Derb]

I tried to inverted V it, but it's just no good. too many snags. I'm hoping that by riding on pulleys the antenna will stay up for good. Wife wants me to get a tower and quit farting with trees. Come spring I'll be happy to make that happen.

No radio operating = s&%# quality of life.   

tomorrow and tuesday looks good to putting it back up.

[K1JJ]

The only issue would be when it rains and/or it turns into ice it will short across both wires if the wire is not insulated.

Now that's a good point...

Is it the added CAPACITANCE that the ice or water adds that makes openwire change characteristic impedance or will the DC short of ice/water make a difference with bare wire?  The reason I axe is I thought water (aside from acid rain) did not conduct well - it was the minerals in the water that made it conductive.  Maybe the stray minerals sitting on the spreaders and bare wire make a big difference when they mix.

I guess my question is, how much is the effect from capacitance (which would affect insulated wire too) vs: the effect from actual contact with the bare wires?

I remember having a dipole on Nantucket and had to spray it down every few days due to the shorting action of the salt spray. It was that bare openwire stuff with the little white insulators. Salt is an extreme case of course. I wonder how it wud have been if the wire was insulated?

T

[flintstone mop]

Somebody PLEASE correct me.....But I do bvelieve that Timtron is using open ladderline 6inches spacing(?) MORE??? and transmitting 50kw, WBCQ transmitters, through it. And it works every day with no snags. PLS click on link.
Tim would not do anything that would compromise reliability.

Phred



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