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Author Topic: Trimming Wires for Dipole Antennas Question  (Read 3455 times)
N1IRF
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Posts: 37




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« on: November 14, 2013, 01:05:15 PM »

I was looking at a dipole antenna and I had a question about removing wire insulation.  I noticed at the insulator end of a dipole, the end of the wire will have about two inches of bare wire.  Then there is usually about two to four inches of wire insulation (that is were the wire goes through the insulator hole) followed by about two inches on bare wire.  My question is:
1. What is the best way or method to remove wire insulation (about two inches) and leave some wire insulation to protect the wire when it goes through the insulator hole?
2. Is it easier to remove all the wire insulation and use either liquid tape or heat shrink tubing for the part of the wire that goes through the insulator?
3. Is it better to leave the wire insulation on and not trim it (wrapping and crimping the end of the wire)?

Thanks.       
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WB2WIK
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Posts: 20561




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« Reply #1 on: November 14, 2013, 01:26:44 PM »

I have no idea why anyone would strip the insulation at the ends of a dipole made of insulated wire.

I wrap the insulated wire through the insulator and tie a knot there, using the wire.  Works fine, lasts years, no stripping involved. Smiley  If the wire is very stiff (like single conductor hard drawn or copperweld), just threading the wire (with insulation) through the end insulator and then wrapping it back on itself a few twists tightly bunched close together works fine and will withstand a lot of tension without unwrapping.
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G3RZP
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Posts: 4447




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« Reply #2 on: November 14, 2013, 01:30:30 PM »

I never bother. If the SWR is below about 1.7, I live with it. But I use tube PAs which have no problems with such an SWR. My 40m dipoles are all slopers, with feeders tuned such that the unwanted ones are reflectors, but they work well - to give more than DXCC on 40.
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AA4HA
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Posts: 1386




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« Reply #3 on: November 14, 2013, 01:32:23 PM »

There is no need to remove any insulation from the end of the wire if you are just bringing it back around the insulator to anchor to the lead.

If you had a real reason to do that (to leave insulation on part of the wire and to use it as a sleeve) you could strip off 2-3 inches of insulation and discard it. Then strip up at the point where you are going to tie the end back into but do not totally remove the insulation, only pull it back an inch or so.
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
WB2WIK
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Posts: 20561




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« Reply #4 on: November 14, 2013, 01:42:22 PM »

It just occurred to me maybe this is about the "center" insulator for a dipole, where the transmission line or balun makes electrical connection to the wires??

If so, then of course the wire needs to be stripped, to make those connections.  But if doing that, there's no reason to use any more insulation anywhere beyond the part that's stripped to make the connections.  Just strip as much as needed to make connections and leave it at that.

I usually solder those (feedline) connections, although they'd probably work just as well with a good mechanical bond.
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N1IRF
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Posts: 37




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« Reply #5 on: November 14, 2013, 01:44:53 PM »

It just occurred to me maybe this is about the "center" insulator for a dipole, where the transmission line or balun makes electrical connection to the wires??

My question refers to the end insulators and not the center insulator; but, thanks for the insight.
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WB6BYU
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Posts: 13126




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« Reply #6 on: November 14, 2013, 03:20:25 PM »

There is no reason to strip any wire at the end of the antenna.  I never bother
doing so, and put up lots of wire antennas.

Yes, you'll see drawings where the wire is soldered around the insulator - this is fine
for bare wire, and might help to keep the connection from becoming intermittent
with age.  (On the other hand, solder wicking up stranded wire can weaken it
because it forces all the flexing to happen at one point.)

If you are using insulated wire, just tie it to the insulator, or, for stiff wire, wrap it
around itself a few times.  I leave enough end hanging down so I can prune the
length without having to retie the insulator.

There is a subtle difference in electrical length between bare (soldered) and insulated
wire in this application:  in the case of insulated wire you have added some inductance
where the wire is knotted, and sometimes the equivalent of a shorted stub if you tie a
loop knot.  I find that I need a bit more wire for the same resonant frequency then I
would if the wire were bare, and even if the knot is tied exactly the same, the effect
on the resonant length of the antenna will be different if the knot is tied at different
places along the wire.  With bare wire you've effectively added a bit of capacity hat
instead, and may see some similar variations.

But the standard formula for the length of a dipole is only an approximation anyway - the
variations due to height above ground and other physical factors will probably cause more
variation than how you tie your insulators.


Don't get too hung up in the details.  Just tie a knot in the insulated wire and leave a bit
of the end hanging down so you can trim it.  It's easier and works just fine.
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WB6BYU
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Posts: 13126




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« Reply #7 on: November 14, 2013, 04:06:25 PM »

But if you do need to remove some insulation in the middle of the wire, here are
two ways that I do it:

1) if it is very close to one end, figure out how much of a gap you need and strip that
much off the end of the wire.  Then put your strippers around the wire where you
want the gap to be, cut through the insulation, and slide the insulation along the wire
enough to open a gap where you want it.

2) Use your strippers or a knife to cut through the insulation at both ends of where
you want the gap.  Then take a knife blade and whittle the insulation off the top of
the wire.  This usually works best when I can chuck one end of the wire in a vise and
pull the knife towards me, keeping it fairly flat to the wire, so it just slices off the
top of the insulation.  Once the top of the insulation is sliced off, the rest of it should
just pull off.  I've used this technique to strip the insulation from 50' of wire relatively
quickly - almost as fast as I can walk backwards pulling the knife blade.  Sure is easier
than using strippers to take off a couple inches at a time!
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G3RZP
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Posts: 4447




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« Reply #8 on: November 15, 2013, 03:07:18 AM »

You are likely to have soft drawn copper wire if it has insulation. That will stretch - how much depends on the length (weight) and if a dipole, whether the centre is supported. It can be useful to pre stretch the wire - I have stretched as much as 18 inches out of 66 foot length, and it work hardens the wire.
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N4NYY
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Posts: 4746




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« Reply #9 on: November 15, 2013, 04:31:18 AM »

It just occurred to me maybe this is about the "center" insulator for a dipole, where the transmission line or balun makes electrical connection to the wires??

My question refers to the end insulators and not the center insulator; but, thanks for the insight.

My end insulators on my dipole do not have stripped wire. I twisted the wire as is, fully insulated. The only places I stripped were where I connect to the traps and balun.
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W4VR
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« Reply #10 on: November 16, 2013, 08:45:28 AM »

Why would you want to strip the insulation off the wire?  What I do is make my dipole about a foot or longer on each leg and wrap the excess wire that goes through the insulator around the wire.  This way you can adjust the length and you do not have to solder anything.  The only place where I solder my connections is at the feed point.  Also, keep in mind that leaving the insulation on the wire lowers the velocity factor slightly...for example a 65-foot dipole with the insulation would resonate just above 7.0 MHz...w/o the insulation it would resonate around 7.2 MHz.
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