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Author Topic: Inverted V  (Read 563 times)
ROBFINDLAY
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Posts: 76




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« on: March 20, 2007, 02:22:19 AM »

Hey, I'm thinking of putting up one of those 33ft MFJ fiberglass masts to hang a dipole on for an inverted V, is their a calculation or "rule of thumb" on how narrow or sharp the V ought to be?
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KB9CRY
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« Reply #1 on: March 20, 2007, 05:38:21 AM »

Rob, what radio books do you have?  ARRL Handbook?  ARRL Antenna Book?  Using eHam for basic research may not be the most effective way of learning the basics.  We try to answer your questions as best as possible but we may leave out other aspects that should be learned as well.

Here's one calculator:

http://www.hamuniverse.com/dipivcal.html
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AA4PB
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Posts: 12700




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« Reply #2 on: March 20, 2007, 05:58:58 AM »

Not critical at all - generally whatever fits your situation. 90 deg is about minimum. 180 degrees is a dipole. Anywhere in between will work.
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K5LXP
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« Reply #3 on: March 20, 2007, 06:11:38 AM »

I hope you're using weight-free wire and coax, because the MFJ 33' pole can only support about 3 ounces from it's end.  You might be better off with the Jackite or Spiderbeam fiberglass poles.

Mark K5LXP
Albuquerque, NM
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K7KBN
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Posts: 2766




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« Reply #4 on: March 20, 2007, 10:06:58 AM »

Experiment with different vertex angles.  Buy or borrow an antenna analyzer and keep good records of the results.  See what effect the different angles have on the feedpoint impedance, and on the bandwidth.
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73
Pat K7KBN
CWO4 USNR Ret.
W3SCM
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Posts: 15




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« Reply #5 on: March 20, 2007, 10:35:22 AM »

Those poles are essentially worthless for this purpose.  Too flimsy in every respect.  Unless you live in an underground house on a flat, treeless plain, there are almost certainly better options to hanging a dipole/inverted V than using a short pole like this.  

If you have to put up a pole, get something that will stay up in the wind, while bearing the weight of the wire, center connector, feedline and tie rope.  You'll also need something to secure the ends of the legs.  You can use rope secured to an insulator tied to the legs, and tie that off at ground level if you have to, but make sure the ends or the wire itself are well above reach.  The ends of the wire  legs themselves will be RF "hot" on transmit and can burn people, animals and other things.

Not meaning to flame, but if you are interested in radio and you can post here, then you have access to a wealth of basic (and advanced) information on antennas including formulas, calculators for lengths, angles, etc.  I suggest you avail yourself of some simple research and save your forum questions for things that don't have easy and easily-available answers.

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WB6BYU
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Posts: 13040




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« Reply #6 on: March 20, 2007, 01:47:31 PM »

As a general rule the flatter the better, but an inverted vee should still
work pretty well on the design band as long as the wires aren't closer
than 90 degrees to each other.  Basically you put up what you can and
tie the ends off wherever available with lengths of rope.

My suggestion is to look around for some telescoping TV masts to use
rather than the skinny fiberglass.  A 2- or 3-section mast should get
the antenna up plenty high, and will support the weight of the coax and
wires as well.  I'd suggest at least one set of guy ropes to keep it from
bending too much in the wind, but it may be fine just attached to the
eaves if you don't try to go up too high.


Whatever you put up, I always suggest adding some sort of pulley or
ring at the top with a halyard for raising your antenna.  That makes it
easy to lower the antenna for tuning, or to try something different.
One thing that I've done with a metal mast is to put a 4' board (1x2 or
2x2) crosswise on top with a U-bolt, then hang a halyard from each
end of it.  This keeps the antenna out away from the metal support
and allows me to try out two antennas on the same mast.
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ROBFINDLAY
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Posts: 76




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« Reply #7 on: March 20, 2007, 05:01:08 PM »

Sorry guys, I grew up around this stuff with an old man who didnt give 2 sh*ts about teaching me anything, now that I'm at a point in my life where i can get started on this hobby that I was ALWAYS genuienly inerested in my thirst for knowledge is insatiable.  Unfornatly I am impatient by nature.

I'm also trying to make up for lost time in years and lost time with the old man.

Forgive me.

p.s. It also doesn't help that I have a fear of heights so bad I will have a panic attack if I try and force it, and scoliosis so bad that I'm not supposed to lift over 20 pounds.

So again forgive me.  

p.s.s. Not as a flame to them, but the Utah Ham club is really kind of mormon-cliqueish and I feel like an outsider not being mormon one of them.  They're all friendly as heck but it does feel insular so I'm not even sure if I'll be able to get help putting a tower up. So I feel kind of desperate.

Thats it.
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VA7CPC
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Posts: 2358




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« Reply #8 on: March 20, 2007, 09:59:51 PM »

I have a 31' Jackite pole, and I don't know that I'd use it for a permanent installation.  It's light and flexible -- superb for portable use.

For fixed use, either a metal pole or large-diameter PVC pipe would be my choice.  Either one is light enough for one-man installation.  Put guys near the top, and halfway up if necessary.

Put a pulley on the top (as suggested by another poster) to hoist the antenna.

You could get a copy of free EZNEC from:

http://www.eznec.com/demoinfo.htm

and antenna-model inverted-V's to your heart's content.  It's reasonably easy to use -- I was expecting something way hard, and was pleasantly surprised.

You'll learn much more playing with EZNEC, than by asking partial questions and getting partial answers.

     Charles
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W5CEM
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Posts: 29




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« Reply #9 on: March 25, 2007, 06:30:59 PM »

I found a wealth of info on inverted V's on Cebik's www page...he did a lot of testing, and found 90 degree between legs to be not so good, he recommends 110 degrees.  We are starting to experiment with a design with 52 ft. legs, fed with 300 ohm line to a tuner for Field Day...google D3+

Then we found a trigonometry calculator online that tells us with 52ft. legs, how high we have to have the center to keep the ends off the ground.  

I have a couple of Jacktite poles...not so good for base station use.  And they only go to 31ft. which is almost no enuf.  

Pushup masts will keep your feet on the ground, with a pulley attached to the top.  There is even a wooden mast thing in many of the ARRL HANDBOOKS that can be tilted up with two guys.  Had one at my house for years!!!  

I keep seeing the DX ENGINEERING ad at the top...they sell a 70ft. antenna fed with 300 ohm ladder line for 40-10 mtrs.  Copy the design for a lot less, then you don't need as high a support.

I know all about clubs that don't seem all that friendly...but keep asking around.  I would hope there is a group that is not so mormon-esque!  But it is hard in that area...

cleve/W5CEM
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ROBFINDLAY
Member

Posts: 76




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« Reply #10 on: March 25, 2007, 08:26:29 PM »

"
I keep seeing the DX ENGINEERING ad at the top...they sell a 70ft. antenna fed with 300 ohm ladder line for 40-10 mtrs. Copy the design for a lot less, then you don't need as high a support.
"

What antenna is that, over at DX Engineering?
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