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Author Topic: SHORT DIPOLE FOR 80 METERS  (Read 3777 times)
KB3KCJ
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Posts: 125




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« on: August 11, 2005, 12:23:14 PM »

I am moving to a limited space lot and probably won't be able to put up one of those 75 feet verticals with a kazillion radials and am considering a shortened dipole for 80 meters.  Without any technical jargon, can anyone tell me how to make the loading coils?  What diameter of PVC and how many turns of the winding?  I can live with a formula, but I keep getting directed to web sites with a lot of technical stuff that I am having trouble.  I plan to feed it with coax or ladder line.  I am trying to get one that will work well on 3.906 MHz.  Thanks for all of your help.
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W4CNG
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Posts: 178




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« Reply #1 on: August 11, 2005, 12:49:21 PM »

I saw a note here recently that showed a shortened dipole.  Each side was 24 feet for a total of 48 feet.  In the middle of each side of the dipole was a loading coil 3" diameter 3.5" long with 105 turns of #18 solid formvar style wire (varnish insulation). Feed with 50ohm coax.
Good Luck
Steve W4CNG
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W5RH
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Posts: 11




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« Reply #2 on: August 11, 2005, 01:00:37 PM »

This is a good one to build but pretty narrow SWR BW.

Wayne, you might take a look at an article I wrote...visit http://bvarc.freeshell.org/bulletin.htm and go to the May 2004 newsletter.   Antenna Loading Part 2.

This walks you through the method to figure antenna size and coils required.

Keep looking on the web, there are many 'off the shelf' designs for shortened 80 meter sky hooks that should fill your need.  ARRL TIS has some too.   GL Rick -- W5RH
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KZ1X
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Posts: 3227




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« Reply #3 on: August 11, 2005, 01:13:39 PM »

How would you like to build one that was less than 30 feet long, and had NO traps, and had performance similar to a regular half-wave dipole?

It needs to be up 60 feet to work conventionally (not NVIS) and it needs a 2:1 balun to feed a 50 ohm coax.  

People think these things are not possible, but, they are.

I have the EZNEC file to prove it.

I also have a design for a 10' diameter magnetic loop that works similarly well, and only needs to be up 8 feet off the ground.  I have built the same antenna for 20, 40, and 80 meters, so, it's not just a "brag" ... it's been done.
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WA6BFH
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Posts: 646


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« Reply #4 on: August 11, 2005, 01:17:32 PM »


W5RH, I could not find the page you reference.

Maybe you could go to it, and cut and paste the exact URL for us?
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WB6BYU
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Posts: 13038




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« Reply #5 on: August 11, 2005, 01:22:36 PM »

One reason it is hard to find specific designs is that
the bandwidth can be very narrow, and the actual resonant
frequency will vary quit a bit depending on the exact
environment where the antenna is installed (height above
ground, nearby metal, wire diameter, etc.)  No matter how
carefully you copy a design, you'll still need to make
adjustments for your specific needs.

The ARRL Handbook/Antenna Book have design information
so you can design an antenna of a size that works in your
situation, using whatever size pipe or other former you
happen to have around the house.  If you want to give us
a desired resonant frequency and maximum wire length,
I'm sure one or more of us can come up with an antenna
to fit.
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W3JJH
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Posts: 1422


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« Reply #6 on: August 11, 2005, 01:35:45 PM »

I've used a VanGorden Shorty dipole for several years on with good results on all MF/HF bands.  It's 70 ft long with loading coils part way out on each side and fed with ladder line.  A tuner is required.
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W5RH
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Posts: 11




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« Reply #7 on: August 11, 2005, 01:36:07 PM »

Thanks.

URL is   http://bvarc.freeshell.org/bulletin.htm

Then select the May 2004 Newsletter, and view the PDF.

The article I reference, does not have a specific URL due to it being a PDF.

Hope this helps....Rick
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W5RH
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Posts: 11




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« Reply #8 on: August 11, 2005, 01:43:16 PM »

Sorry....try this:

http://bvarc.freeshell.org/newsletter/bvarc052704.pdf

Rick W5RH
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K4SAV
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Posts: 1825




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« Reply #9 on: August 11, 2005, 02:14:55 PM »

Just how much space do you have? You can make a shortened dipole just about any length, but the shorter you go, the more loss you will have, either in the feedline or in the tuner. If you add a loading coil, and feed it with coax, the bandwidth will be narrow, and it will be useful only on one band. If you have 100ft or so, you can just put up a dipole that long, feed it with ladder line and a tuner, and have a reasonably efficient antenna.  You can also use it on 80 thru 10 meters.  Performance wise it will be the same as a G5RV. You can also do things like bending the dipole or allowing the ends to droop down.  If you want to read about losses in shortened antennas, try
http://www.w8ji.com/short_dipoles_and_problems.htm

Jerry, K4SAV
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KA0GKT
Member

Posts: 555




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« Reply #10 on: August 11, 2005, 02:25:32 PM »

Generally speaking, an antenna which has been shortened will have a narrower bandwidth than that of the full sized antenna.   Folks who work HF mobile have dealt with this problem since day one of mobile operations.

An antenna as short as 16' can be made to resonate in any of the HF amateur bands.  I know of people who have used Hustler resonators as the "Loading Coils" on shortened dipoles.  A pair of "Hamstick" antennas can be fashioned into a nice little dipole by fabricating a mount using a pair of 3/8-24 through hole mounts and a couple of pieces of angle iron.

Loading an antenna often will make multiband operation difficult, however, if you have room for a 40 meter dipole, feed it through open wire feed line or ladderline and a tuner and it ought to work pretty well on any band.

Good luck ES 73 DE KAØGKT/7
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KG4PBG
Member

Posts: 26




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« Reply #11 on: August 11, 2005, 03:04:46 PM »

I purchased loading coils from HyPower Antenna Co. to make an 80m dipole that was about the same length as a 40m dipole.  

I was very pleased with the quality of the coils and I thought the price was reasonable.  The coils also came with good instructions.  

The bandwidth is rather restricted with the coils though.  You'll need a tuner to cover 75m and 80m.

link:
http://www.angelfire.com/electronic/hypower/webdoc1.html

73,
Richard
KG4PBG
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W6HB
Member

Posts: 38




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« Reply #12 on: August 11, 2005, 04:17:35 PM »

If you can fit an inverted vee or flat top configuration 88' long, check it out on W4RNL's web site. It is a good compromise antenna that I have used on 80 through 10 with tuned feeders. The plus is that it is an  double extended Zepp with broadside gain on 20 as well.
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N6AJR
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Posts: 9891




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« Reply #13 on: August 11, 2005, 04:36:17 PM »

alpha delta also sells a couple of shortened antennas for dipole or sloper use, and I am sure if you do a search on the net on homebrew shortened 80 meter antennas you will find one you can roll your self.  lots of them use  the center conductor from some rg58 ( solid dilectric) and some 3 inch pvc pipe for forms..
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WA3IRJ
Member

Posts: 119




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« Reply #14 on: August 11, 2005, 06:12:20 PM »

I have the alpha delta "dxcc". It is a shortened 10-80 meter dipole( center fed 50 ohm coax). It is about 82 feet long. It is actually a fan dipole. It works great on 20,40,80..somewhat marginal on 15 and 10. But as many have stated, the dipole uses coils on each end, and it a high Q antenna on 80...witout a tuner the band with can be narrow. But a good tuner will spread it out some. I have worked almost all states on 75 meters with it at 45 feet in an inveted V...No complaints here. I will soon have it up at 70 feet, that should help. It also works extremely well on 20, and 40 !
73
JohnB
KB3LXY
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