FOLDED DIPOLE

[AE1CT]

DOES ANYONE KNOW IF I TAKE A 75 METER DIPOLE 126FT LONG AND FOLD IT BACK ON ITSELF HOW FAR APART (SPACED) DOES THE WIRE THATS FOLDED BACK HAVE TO BE FROM THE DIPOLE WERE THE COAX ATTACHES TO. I ONLY HAVE 75FT OF SPACE AND CANT PUT UP AN INVERTED V OR A FULL SIZE DIPOLE. THE REASON FOR CAPS IS THAT MY EYES ARE NOT THAT GOOD AND I CANT READ WHAT I WRITE WITH LOWER CASE. ITS HELL GETTING OLD.

 

[wa3dsp]

I came across this commercial folded dipole in a search. It looks interesting. It is about 82 feet long. You could probably accommodate a longer length by angling the antenna.

http://www.spiromfg.com/folded%20dipole%20antenna.htm

There are shortened antennas like the G5RV and Carolina Windom that would fit in your space. It would be harder to do 160 meters though.

Here is a link to some general folded dipole info -

http://www.qsl.net/w4sat/fdipole.htm

The bottom line is that the total length end to end is the same as a dipole - 1/2 wavelength. So you cannot just fold back what you have. A folded dipole also has a 300 ohm impedance so you would need to use a balun to feed coax. You could use open wire line to a balanced tuner or remote balun.

Understand about the eyesight. No problem.

[W7TFO]

        
The RCA 80/10 meter compact dipole.



    
                      26'                            26'
         @---------------[insulator]--------------- @
            '                                                      '
            '                                                      '   12'
            '                                                      '  
         @ '----------------[FEED]----------------' @
                                      .  .
                                      .  .
                                      .  .
                                      ^ ^
About 54' overall length, 12' high on masts.
@ = support insulator.
Left and right halves are symmetrical single pieces of wire.
Top wire needs to be 45' AGL.

73DG

[WA3VJB]

THE REASON FOR CAPS IS THAT MY EYES ARE NOT THAT GOOD

Here's a trick that might help anywhere you're on the internet or writing email --

Your keyboard, lower left CTRL, hold that down and then in the upper right find the plus + sign.
Push plus as many times as it takes to get comfortable.

To reverse, hold CTRL and the minus - sign

[KU8L]

I see....

For 4 years I used nothing but a Carolina Windom cut for 40M.  With a tuner, either in the radio, or external, it works all bands from 40 thru 6.  At 35 feet high and about 66 ft long, it gave me the ARRL TPA award, WAS in one RTTY contest, 180 DXCC countries, etc.  It was cheap and easy and fit in my yard.

For several of those years, I tried to get it to work on 75/80M as well but it would not. 

Then I see that Radio Works, who sells the commercial version of these, has what they call a "compact 80M version---still only 66 feet long.  Runs any band from 80-10/6.

Essentially, it is the 66' forty version with a set of Drooping extensions that hang down below the main wire and get attached to the center insulator with about a 5' pc of nylon paracord.  So the extended sections make it  about 130 ft of wire .

THis is NOT a folded dipole.  I dont think a folded dipole is any shorter but is more broadbanded and has a different feedline impedance than a normal dipole--in a folded dipole the main wire is continuous across the center and feeds at the center of the second.

Anyway, I tried adding the drooping extensions to my 40M windom and it works pretty well.  I think it has altered the operation on the higher bands but they still all work.  It is a little fussier to tune but works.  With the MN-7000, I am able to get it to 1:1 nominal across the entire band although there are bands that will not tune using the internal tuners on most of my newer radios.

If you do this, use a good coax line choke or two as RF in the shack can be an issue.  Also know that Tuning thru coax is a lossy proposition--when the SWR in the shack says 1 to 1, the coax is still running miss-matched by a lot in some cases.  But the antenna will work.

To try out a simple test, just take a regular dipole cut for 75/80M--hang the part you can stretch out and let the rest bend, fold, turn or whatever.  You might have to adjust it in length, but it will work.

Or use a vertical....

Curt
KU8L

[N2DTS]

For many years I used a shortened dipole for 80 meters using coils in the center of each leg.
I had 100 feet between a tree and a 40 foot mast on the other side of the house.
Just a bit of B+W coil stock over an insulator, wimpy coil, maybe 16 gauge wire, about 15 turns, and the swr was 1.2 to 1 in the AM window.
Since the antenna was 100 feet long, it did not hurt the performance much at all.
The antenna took 700 watts carrier for many years till I took it down.
It ran over the house lengthwise and caused havoc in the phones and TV, so I put another antenna at right angles to the house, in trees that gave me 120 feet in length.

I have a 40 meter dipole about 30 feet from the 80 meter one and they do not seem to interact much.
I enjoy the lack of power limitation and not needing an antenna tuna.
No traps, no baluns, no rf in the computer problems, balanced is nice.

[Steve - K4HX]

Folded arrangement has been done by several AMers. Two notables with good signals are KB3AHE and KD3CN. Info at links.

http://amfone.net/Amforum/index.php?topic=18394.msg128466#msg128466

http://amfone.net/Amforum/index.php?topic=8612.msg78423#msg78423

[W2VW]

Center fed half sized doublet 60 or so feet long can be made to work on 80 meters afer a fashion.

All conductors must be sized for extra current, coupler must be built with high circulating current/voltage, low output/highly reactive impedance in mind. Can be homebrewed. No manufacturer has this on the shelf.

K3L 2005 used a 60 foot center fed doublet. Look at the 75 meter log.

[KK4YY]

The classic 1/2 wave dipole is always drawn as a straight line in a book. It need not be installed that way. Optimally, yes, but not necessarily. The inverted V is an example of this. The acute angle thus formed is often recommended to be no less that 90 degrees. OK, fine.

Now imagine an inverted V laid on it's side. It's a 1/2 wave horizontal V now. So what? It will still work and can be fitted in a smaller space than the straight dipole and requires no single high support as does the inverted V. It will require 3 points of attachment, however. Perhaps the feed point mounted on the house and the ends out to 2 trees each 70 or so feet away. That is exactly what I am using at my apartment. The acute angle is only 70 degrees. It works. It's still a dipole. You can even zig-zag the legs between trees if need be. The antenna police won't break down you door and you'll still get out.

The time honored dipole, even if crunched a bit here and there, is simple, cheap, and will work well.

Don

[Steve - K4HX]

More info on the RCA All-Band Antenna here.

http://amfone.net/Amforum/index.php?topic=32911.0

[K9PNP]

I use a direct-coax-fed inverted V for 80M.  One end is bent back for about 10 feet at about 50 degrees due to lack of space.  Also, it is not in line.  One leg is approximately north-northwest and the other is approximately south-southwest.  Gives me good results.  Like has been said, you just use the space you have and do the best you can.  Any wire in the air will radiate.  The military proved that years ago.

[w1vtp]

Good to work you this afternoon, Gary.  If there is any way you can do a wrap-around on your property I think that would work best for you.  Think about a tuner somewhere along the way to take care of any loading problems coming from a compromise antenna.

This might be a solution for your situation

http://www.k1jek.com/

The Cobra Ultralite Junior works on 75 meters and is 75 feet long.  If you make it up to Near-Fest this spring they usually have a table set up and you can talk to someone.  I have never used one but a friend of mine uses the Senior model and he puts out a strapping signal on 75 meters.  It might be worth a call to them and talk about your problem. Otherwise there are short antenna solutions listed on this thread

Good luck and nice working you today

Al W1VTP

[wa3dsp]

I have a vacation property in Cape May NJ with a lot size of about 60x110 feet. My first antenna was center fed which angled from the front corner to the back corner and then angled 90 degrees to the side in the back and down the pole vertical in the front. It was fed with open wire line and a tuner. It was OK but power line noise tends to be high at the shore and I was not very satisfied.

I then made a loop around the perimeter of the property, total length about 300 feet fed on one side with open wire line. This antenna works far better and the signal to noise is much improved. Both antennas were only about 20-25 feet high. I use this non-resonant length loop on 160 through 10 meters. I did a lot of research on loops and I determined that there is no real need to have a resonant length and in fact in one reference it appeared to work better when it was not resonant.

So my thought would be to try and get four poles up in your yard corners. One of the poles in my case is my flag pole. I bought telescoping 8' aluminum sections, overlapped them a foot and put a couple of feet in the ground. I used pulleys on each pole. It has survived hurricane Sandy and the high winds at the shore without damage.