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Author Topic: paracord question  (Read 4592 times)
K9AIM
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« on: September 02, 2012, 06:15:44 PM »

As a support rope for a fan inverted vee, I am wondering from experienced wire antenna folks if Dacron is preferred and/or if Paracord is a viable option?

I want to hang a fairly permanent inverted vee and happen to have some paracord (Commercial Type III, 550 Parachute Cord) lying around and was wondering if it is a good choice or too weak?  Anyone know if it is UV resistant? Evidently it is good enough for parachutes...

rating is 550lb minimum breaking strenth.  Anyone used this?  It's pretty inexpensive at Amazon and available in many colors...
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K3GC
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« Reply #1 on: September 02, 2012, 06:27:14 PM »

Nylon has considerable stretch and is very vulnerable to uv.  Dacron is a much better choice.
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KE5PPH
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« Reply #2 on: September 02, 2012, 07:36:42 PM »

I've had good luck with it,but after a year depending on your QTH. It starts to get brittle, because of UV exposure. long term, go with the Dacron.
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KC7YE
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« Reply #3 on: September 02, 2012, 07:44:27 PM »

Ditto on paracord, but works fine for portable/FD set up .

By the way every knot in (any kind of) line will weaken line by 30 -50 %, depending on knot used.
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K2DC
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« Reply #4 on: September 03, 2012, 03:20:58 AM »

I have 3/16" paracord on my wires.  It's been up almost 9 years and still in great shape.  I had to move one earlier this summer for tree work, and it's not brittle at all.  Mine is Olive Drab, which I'm sure helps with UV.  I found a 1200' roll of it on eBay 10 years or so ago for peanuts.

73,

Don, K2DC
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K0ZN
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« Reply #5 on: September 03, 2012, 10:43:50 AM »

If the Paracord has a 550 lb. break strength it is a LOT stronger than #14 copper antenna wire !   I have seen heavy ice loading on my antennas with # 14 copper
and none of them failed.  Actually, I am pretty sure that is probably higher than # 12 copper.  What will happen to your end supports if you put 550 lbs of pull on them !??!

Think about this: Unless your span is in hundreds of feet, the tension pull on the antenna and rope system will likely be in the order of 15 to 30 lbs at most.
You don't want to tension the antenna like a piano wire!  You need a small amount of slack and sag....such being the case, you will likely only have 15 to 25
lbs of pull. .....and your paracord is rated at 550 !   If that stuff degrades 15% a year, which it likely won't it would last for YEARS !  You should pull your
antenna down once a year and inspect it anyway and if you do that, you will catch a problem before it fails.

The knot you use to tie thing with has a great impact on strength. Learn to tie a Bowline knot!  It is very simple and is a knot that is self tightening and
will carry 90% of the strength of the rope. This is the "go to" knot for applications like this.

Some of the other rope types that were recommended are "better", but the question becomes does it make economic sense.  If you want to put up an antenna and not
mess with it for 10 years or have severe wind or ice, then you probably want something better than paracord.  If not, then you can bet by with a cheaper rope.
Again:  How much tension will your SUPPORTS take before they fail or an eye bolt pulls out, etc.  ??! You could use Extra High Strength steel cable with 3,770 lbs of breaking strength, but what is the point if your hardware store eye bolt fails or pulls out at 120 lbs. of tension?!   A chain is no stronger than its weakest link.

FYI: if the rope is going to be rubbing something like a tree, you are into a totally different game. Synthetic ropes will not last long at all if they are subject to
rubbing. If there is rubbing, you need steel cable.

Also, if you are going to use a pulley at any point, use a good one with a DEEP "channel" on the pulley wheel so the rope will stay on the wheel. Cheap
pulleys have a shallow channel in the wheel and the rope can jump out of it in some cases and get stuck between the wheel and the side of the pulley. That can be
a major problem in some cases.

73,  K0ZN
« Last Edit: September 03, 2012, 10:48:52 AM by K0ZN » Logged
WB6BYU
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« Reply #6 on: September 03, 2012, 11:24:05 AM »

Quote from: K0ZN

...Learn to tie a Bowline knot!  It is very simple and is a knot that is self tightening and will carry 90% of the strength of the rope. This is the "go to" knot for applications like this.



Actually, more like 60% of the strength according to this study:

http://www.bethandevans.com/pdf/8_strength.pdf


Now my personal favorite in its place is the figure-8 follow-through, though I used the
bowline a lot previously, and still do at times, especially when tying a rope or wire
through an eye.


We had a long thread on nylon rope a year or two back.  Most modern nylon rope is
made with UV inhibitors, and should last at least 10 to 20 years or more, even in the
sun.  Polyester, including Dacron(R), is standard on sailboats because it is more
resistant to sunlight, but for most ham use there won't be a lot of difference if the
nylon rope comes from a reputable manufacturer.

The rope construction can be important in some cases.  I often toss a rope over
a tree for portable use, and a solid braid rope has lower friction than a kern-mantle
type construction (as is used on paracord.)  This is because the inner strands of
the paracord take the weight not the outer sheath, which is then softer and tends
to snag more easily on rough bark.  I'm still using the remnants of a spool of crab pot
line that I bought in a commercial fishing shop in Alaska over 30 years ago - a good
tight nylon braid that slides easily over a tree limb.  I reserve that for throwing, and
then use it to pull up another rope so I can reuse the throwing rope at the other end
of the antenna.
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K9AIM
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« Reply #7 on: September 03, 2012, 06:54:24 PM »

thanks for the great, informative replies.  Support is a white pine so the support rope will 'rub'  against the branch I use -- about 45 ft up is the plan... Should I duct tape the part of the rope that will end up being against the branch?  I do not plan to climb the tree but use the string and ball trick to then hall up the support rope...

I guess I can always inspect and replace the rope every few years too.  If my old wire was insulated and some of the insulation has separated from the wire -- do you recommend going with new wire or just using the old stuff.  Does the wire performance degrade much
from oxidation, etc?

I know I can learn by doing but it is nice to be able to ask those who have already 'been there; done that' -- and it may save me a few bucks over time Wink
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WB6BYU
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« Reply #8 on: September 03, 2012, 07:15:50 PM »

Typically what I would do in such a case is to toss a rope over the tree, tie the
ends together to make a continuous halyard, and use that to hoist up a pulley.
The rope that goes to the antenna comes through the pulley and down to a
counterweight near the ground.  That way the rope that goes over the branch
doesn't move, reducing wear.  The counterweight limits the strain on the wire
when the tree moves in the wind:  sometimes I let the weight sit on the ground
most of the time, only rising when the wind is strong enough.

For portable operation I'd just toss a rope over the tree and tie it off towards
the end of a branch:  the branch provides tension by bending.
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K0ZN
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« Reply #9 on: September 03, 2012, 07:17:17 PM »

Hi, again.

If the rope is going to literally contact the tree and rub, it won't last long, especially if you have much wind or continuous wind. I can guarantee it will fail
at the worst time.  i.e. About mid winter!  That is just Murphy's law.  If you are going to have a support "rope" in a tree, and rubbing in ANY manner, be it in the crotch of a V of limbs, having a branch rub on it, etc. you really want wire or steel cable as it is many times more resistant to abrasion than any man made rope. You could easily splice a piece of steel cable in for the section that touches the tree or just use a long enough piece to go up and over the tree leaving some extra beyond the tree (on the antenna side) then run synthetic rope between the end of the steel cable and the antenna. You can get 1/8" steel cable in modest lengths pretty cheaply at the hardware store. The back up plan to me would be something like 1/4" or 3/8" Nylon rope. Then keep a close eye on it with binoculars ! I highly doubt duct take would do much. What might work would be to cover that part of the nylon rope with clear vinyl tubing. Somebody may have another idea or a better one, but I don't like antennas coming down on an unplanned basis and would take the conservative approach with steel cable. In my part of the world, seeing your antenna laying on the ground when it is 11 degrees
the wind is howling and snowing hard is pretty depressing, so I make a big effort to avoid that scenario!  If the weather is mild the year around antenna repair is less of an issue.

There is almost no point in using insulation on a wire antenna. MOST antennas are made from bare wire. Weather/corrosion does not affect it at all for all intents
and purposes. NO commercial military, marine or commercial HF systems use insulated antenna wire. Insulation will cause the electrical length of the antenna to
be slightly shorter than what might be the calculated length from formula. I guess is you lived in a salt water environment it might be a slight positive, but I have been
on several ocean going ships and none of them had insulated antenna wire. Again, the oxidation does not measurably impact conductivity. Personally, in nearly
50 years of hamming and building many antennas I have never, ever used insulated wire. If you have insulation that is half off some portions of the antenna, I would
go ahead and remove it. All that would serve to do is catch more wind and ice and give no benefits of any kind. If the wire is mechanically strong and undamaged
there is no great advantage to replacing it.....just strip the old insulation off.

You will probably get some varying suggestions in this matter..........

73,  K0ZN

P.S.  Just read WB6BYU's idea. A good one.  If you have a pulley system, the rope in the tree does not move (the movement is handled by the pulley) and has less abrasion. 
        However, if there is some point the tree will rub on the rope, even on the pulley side, in the wind, it is a bad situation.

« Last Edit: September 03, 2012, 07:20:52 PM by K0ZN » Logged
K9AIM
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« Reply #10 on: September 03, 2012, 07:55:48 PM »

Again, thanks for the excellent replies!  Actually I am asking these questions because my former support rope did break (and it was 1/4" or 3/8" nylon rope) in the winter (near the end of last winter).  The antenna fell and the coax caught on a branch below so the antenna was still 'up' somewhat.  Afterwards, it still worked but less than optimally  Wink  When I took it down the coax insulation was worn down to the braid where it had landed and hung up on a lower limb. it was a fan inverted vee (40, 30, and 20 meter legs) and somehow stayed up for 3 and a half years before breaking...  Guess I was lucky.  The white pine with its year round needles does guard the antenna some from ice -- I am in the Indianapolis area...

I replaced it with a G5RV I had bought a year earlier for $10 from a ham who was leaving the airwaves.  That G5RV has served me okay since then -- on 20 meters it has been great -- but on 30 and 15 and 10 I am missing my fan inverted vee... 

I am finally going to go back to the fan dipole -- hence the questions.  the g5RV is bare wire and the old fan has the insulated wire.
I may use the dark green paracord to tie down the ends -- white twine isn't nearly stealthy enough (not that I have any restrictions).
the pulley sounds cool but it is another expense and I may just try to protect the branch rub portion and then inspect it every so often.


How loose do you keep the legs?  I've noted in high winds the legs all dance like a daddly long legs -- they are spread horizontally and not tied down to the same spots.  I guess some give is definitely in order... 

also, can the length of the coax potentially be a problem or is that a misconception?  I am going to switch from old coax length of about 85' to a new length of 110'  (would say 105 or 115' be better or does it not matter?)  I am using wireman 118 (RG-8X) and I have an auto tuner in my rig (Ten-Tec Jupiter)
« Last Edit: September 03, 2012, 08:10:57 PM by K9AIM » Logged
WB6BYU
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« Reply #11 on: September 03, 2012, 09:45:14 PM »

Insulated or bare wire mostly doesn't matter.  I have seen stranded wire get
pretty corroded between the strands, especially in a corrosive environment,
and the insulation can help to prevent that in some cases, or it can hold
water in so the wire doesn't dry out as quickly.

I use almost entirely stranded, insulated wire for antennas, because I get
it cheap ($5 for 5000 feet at the last hamfest).  I tend to use thinner wire
and my antennas are more temporary:  with small wire the insulation provides
a large part of the strength, so when the insulation cracks in a couple years
the wire breaks easily.  Larger wire is better for more permanent antennas,
but I'm always experimenting and/or building temporary portable antennas
for Field Day, ARES, etc., where stranded wire works well.  (Commercial
insulated antenna wire will hold up a lot better in the sun than the common
PVC insulated hookup wire I normally use.)


I've never found cutting the coax to a specific length to give any advantage.
The tables found in some of the older books assume that the shack is at a good
RF ground, which isn't always the case (especially on the higher HF bands).  A
coax length that minimizes common mode currents when the rig is grounded
will be the worst case when it isn't, such as a QRP rig sitting on a picnic table.
Unless you need a particular length coax for matching, like a quarter wave of
75 ohm coax in a 50 ohm system, I'd just use the shortest coax that reaches
to the antenna.  Or whatever I have handy that will work.

The original G5RV had a recommended coax length because of the low input
impedance on 80m when used with tube rigs:  many such rigs had a much more
limited matching range on the low impedance side than on the high side.  (For
example, one rig I remember was rated to match 40 to 600 ohms.)  The G5RV
can run around 12 ohms on 80m (SWR = 4 : 1), so the right coax length moved
it around the Smith Chart to something that was easier for the transmitter to
match.

Otherwise there shouldn't be any magic to the coax length:  the SWR should be
the same along the length, though the specific impedance will change.  The
dipoles should be a good enough match that coax losses will be low and any
impedance transformations will not be enough to worry about.
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KJ4I
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« Reply #12 on: September 03, 2012, 10:27:20 PM »

Im not speaking against dacron rope, in fact, if I had it I would use it but I have always used the quickest and easiest to obtain material for me which is nylon rope and it has never failed me. I have had some of it up for years and it's still going strong.
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KL3HY
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« Reply #13 on: September 04, 2012, 11:16:07 AM »

I've been using nylon line to tie off the ends of my dipole, but when I got my 45' mast and needed to install guy ropes I went with 3/16" dacron.  I don't mind a bit of stretch in a line securing the end of a dipole leg, and if it eventually breaks it's easy to fix.  But when it's a big steel pole that might come crashing down against my house I thought fifty bucks for a 500' spool didn't sound all that expensive.
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KF4ZGZ
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« Reply #14 on: September 05, 2012, 05:46:51 AM »



There is almost no point in using insulation on a wire antenna. MOST antennas are made from bare wire. Weather/corrosion does not affect it at all for all intents
and purposes.



That , sir, is most likely wrong. I would imagine most hams build with what is readily available. Since the Wireman doesn't have a location in every city, and hardware stores rarely sell uninsulated, stranded wire .... most dipoles are probably insulated.
I do agree that basically it makes no difference in how the antenna performs.

Now, one thing to consider is the number one enemy of ANY metal is corrosion. Copper wire is metal. Unprotected, it will corrode and eventually fail.

I build all my dipole with solid copper wire. Insulated because I prefer it. Solid because all you have to do to secure the wire to center and end insulators is wrap it around itself.

I have never ( knock on wood ) had a wire failure in the 13 years I've been using dipoles. Ropes? yep, several times they have failed.
In reality, I don't see why paracord wouldn't work as well as dacron.

Matt
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