KU5E

It is a 2 meter beam. It has a bow tie with a vertical support member for a driven element. It has an lazy H reflector. And it has 10 horizontal directors. The directors are isolated from the boom, while the driven and reflector are not. It is all aluminum construction and has a 2:1 balun at the feed. Below you will find the engineering diags from mmana-gal. (Isometric, Top, Side, Front) I have also attached the graphs, and field plots. Reply and tell me what I have on my hands. When I have an answer I will post it to the wiki.

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Introduction

The windom antenna was developed by Loren Windom in 1929. It was originally a single wire antenna. The windom that is used today is a modification of this original design. It is a compromise antenna. However it does a good job. It is useful without a tuner, when used on bands that are shorter than it is designed for (most of them, more on this later). With a tuner it does well on longer bands.

The original design called for feeding this antenna at a point 19% from one end. This causes he feed point impedance to be around 300 Ohms, requiring a 6:1 balun.

In order to facilitate my construction I wanted a feed point closer to 200 Ohms so I could use a 4:1 balun. I found this point at about 36%. The antenna is made from a half wave of wire with a feed point at 36/64. At this feed point I placed a 4:1 Guanella balun. To this I ran a 40 foot run of RG213 terminated in a 1:1 unun wound on the same core as the balun.

Construction

I used 12 gauge THHN wire. I made the balun and unun with t200-6 toroids I obtained from buxcomm.com. I enclosed these in 4×4 NEMA weatherproof electrical boxes. In order to make this antenna as rugged as possible I used cable thimbles and swages to secure the ends of the wires to the baluns. Then the wire that extended beyond the thimbles was terminated with spades so they could be connected to the lugs on the side of the NEMA box. I placed an eyehook on top so the box can be hung easily.

4:1 Guanella Current BalUn	1:1 Guanella Current UnUn
12 Guage, Thimble, Swages, and Spade	Insulator, Thimble, and Swages
4:1 in NEMA Box	1:1 in NEMA Box
Hook and Spade	Closer

Theory

This antenna is better described as a OCFDipole (Off Center Fed Dipole). But I will call it a Windom anyway. The trick to this antenna is finding a “sweet spot”. The“sweet spot” is the place where you can find a reasonable impedance on the bands you want to use. The higher the frequency the more sensitive the feed point becomes in respect to position.

At its designed length the highest current point is at the center (50/50) of the dipole. The impedance is lowest there. As we move up in frequency, we create
multiple waves on the wire. We have to find suitable feed points where the
current is highest. Through modeling (mana-gal, see previous posts for link) I found two of these points. One at 80/20 with an impedance of about 600 ohms across the bands (with certain exceptions 60 and 17 meters where the impedance is absurdly high, >5:1 SWR), and another at 36/64 with an impedance of about 200 ohms across the bands (the exceptions above are still present).

Measured Impedance at the radio (using MFJ269)

As can be seen this antenna can provide utility in the 80, 40, 30, 20,
15, 12, and 10 meter bands without a tuner, and in the 60 and 17 meter bands
with a tuner.

Formulas

468/f = L (f = center frequency of lowest band to use without a tuner : L = total length of radiator)

L x .36 = Ls (Ls = short side)

L x .64 = Ll (Ll = long side)

L x .25 = Lr (Lr = length of the vertical radiator, although this is arbitrary)

Winding the cores

Make three of these. Take 60 inches of #14 thermaleze magnet wire and fold it in half so you have a loop on one side and two wires on the other. Zip tie the open side on the toroid. Start weaving the wire through the center of the toroid and around in a clockwise direction. Do this without having the wire cross over
it self. Evenly space the winds. When you have made six winds you will have
reached the 12 o’clock position if you started at 6 o’clock. At this point take the wire and take it to the 6 o’clock position and wind it in the counter clockwise direction until you make six more winds and reach 12 o’clock again. Now zip tie this end of the wire and cut the loop. Repeat two more times.

Making the baluns

1:1

One core makes a 1:1 unun (Choke). All you have to do connect it to the SO-259’s making sure that the center goes directly to the other center conductor.

4:1

Cut out a piece of cardboard the size of the core. Take the two cores that are left and glue them to either side of the cardboard making sure that the wires are at the same positions of the clock, so you have four wires at each position 12 and 6 o’clock. Using a continuity tester mark one wire input and output on each core. On the coax side connect the two marked wires (from each core) together and the two unmarked wires together, and then connect these two points to the SO-259. On the other side connect an unmarked wire from one core to a marked wire on the other core. The two wires left unconnected go to the antenna.

Testing the baluns

Connect a 200 ohm resistor to the antenna side of the 4:1, measure the impedance at the SO-259 using an analyzer. This measurements should be close to 50 ohms on centers of all the bands. The same should be done with the 1:1 but using a 50 ohm resistor, with similar results. Now you need to put these in some type of weather proof enclosure.

If I lost you, I apologize, email me and I will do my best to help you (KU5E at KU5E.com). This balun information is in Jerry Sevicks book “Understanding, Building, and Using Baluns and Ununs” and the antenna information is from the ARRL antenna handbook. Have FUN!

UPDATE!!!!

I used this antenna on Field Day to great success. First contact was Alaska!

Art Bell, W6OBB, has created a live feed of his Icom 756 Pro II at his broadcast station in Pahrump, Nevada. Audio is sent from there to the S-Meter site via a private feed. The receiver uses an inverted-v dipole antenna with the apex at 100-feet above ground. It is fed with 450 Ohm ladder line all the way to the rig.

This site has provided me hours of enjoyment. I was an avid fan of Art when he was on Coast to Coast. Now in his retirement you can enjoy his frequent ragchews much like you did his show.

By the way the site that hosts this feed is also very informative. It houses tomes of radio and antenna information. Smeter.net is where I found MMANA. MMANA is an antenna-analyzing tool based on the moment method first introduced in the MININEC Version 3. I other words, it is an antenna analysis and modeling program, that is FREE. I used the version I found here (or Direct Download Link) for a while until I found out that the makers of it had come up with a newer version. The new version, MMANA-GAL, (or Direct Download Link) has been updated with a 3d renderer for field plots, and a more robust optimization routine. Of particular interest is this link which contains archives of .maa (antenna files) for use with the MMANA program.

73 de KU5E

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           This is a quick and dirty 10 Meter beam that anyone can build. I took the original Jungle Job that came with the MMANA –GAL program and sized it down for 10 –meters. Then I ran the optimization to obtain the best F/B ratio and Gain. According to the modeling program, this antenna should make 11.5 dBi at a modest height of 21 feet. The SWR is great in the SSB region of the band (1.1-1.5), and acceptable in the data and CW portion (1.5-2.5). Below you will find all the associated graphs and wire diagrams.

           The element lengths are as follows:Driven: 4.91 Meters or 193 5/16 inchesReflector: Two elements 2.56 Meters or 100 13/16 inches with a 120 Degree angle between them.Element Distance: 2.33 Meters or 91 3/4 inchesI supported the elements with  a  2 x  4. You can use any non-conducting support such as Fiberglass.

Enjoy 73 de KU5E