Third leg on a Windom??

[M0KRL]

A couple of years ago I put up a half size Windom, about 21mtr length, homemade 4:1 balun and direct coax feed, happy with the compromise results, no tuner needed on 40, 20, 10 meters, with SWR below 2:1 on all bands. But now I have found a slightly different design, which adds a second wire from the balun on the long 13.52mtr section, listed as a 3.68mtr, to add usability on the 17mtr, 15mtr, and 12mtr bands, which certainly sounds like a good thing.

My question is, how is this going to affect performance and SWR on the lower bands, space is very much at a premium at my QTH, so any additional usage that I can incorporate is a good thing. Just wanted some input from the forum before going ahead.

Karl, M0KRL.

 

[wavrider]

Karl, Do you have a link to this third leg design? A picture sure would be nice so look at before I try to answer your question.

I have never heard of a 3 leg Windom or OCF. Both types of antennas work on current feed points. I would think throwing a 3rd leg into the mix might mess up the feedpoint impedance, or it might not?

 

[M0KRL]

I dont have a picture, but it is quites simple in design, it seems to be a parralel wire from the balun seperated from the longer wire with a few insulators of about 100-150mm length, just like a very wide ladder line at 3.68mtr length, it looks a interesting adaptation, as long as it does not spoil the main bands.
Just found a thumbnail pic,,
Many thanks for your input. Karl, M0KRL

 

[wavrider]

That may work, sorry late posting but work kept me busy this weekend.

The concept is interesting, sort of like a fan dipole except it is an OCF dipole using a third leg to catch other bands.

Build that thing and see how it works. Heck send me the dimensions and I will build one I have the next couple days off and a few empty pulleys on the tower.

Yes please send dimensions and I will build it and sweep it with the 259B and see what it does. The thumbnail has dmensions but not clear enough to read it. Thanks

 

[M0KRL]

The short leg is listed as 6.76mtr, the long leg is 13.52mtr, with a standard 4:1 current balun, fairly standard layout for a 40, 20, and 10mtr OCF, the third wire is 3.68mtr, strung from the balun as a parallel along the long leg, no information about the spacing distance, but i have some 120mm plastic spacers I am going to try tommorow.
I will let you know my results, but the listed report is less than 2:1 on 40, 30, 20, 17, 15, 12, and 10mtr, without a tuner!?? Time to get the ladder out and find out. Good luck with your testing, Karl

 

[wavrider]

Must be antenna building days.

I Got the vertical up yesterday 10-15 meter.

Rotatable dipole 12/17

The Mosley TA-33 up on the tower also.

Thanks for the dimension I will build it today and see how it works.

 

[W5LZ]

Interesting, looks like a 'fan' OCF doublet. How will that 'new' leg affect the lower bands, or the 'old' antenna? I have no idea, but I would bet that it will. There's a possibility that it will 'enhance' the radiation pattern of the 'old' antenna, but I wouldn't bet on that. It will definitely change the antenna's radiation patterns, probably just like adding elements to a 'fan' dipole changes it's patterns. Hopefully, the addition of having the capability of using a formerly unusable band(s) will make those changes worthwhile.
- 'Doc

 

[M0KRL]

I have added the extra section to my antenna, initial impressions are a little dissapointing, I was expecting big things, firstly on 40 mtr, the swr seems to have increased just a little, on 20mtr the swr has come down quite a lot which was unexpeted, no change at all on 10mtr.
Now the big question, 30mtr is still unusable, 17mtr the swr has come down a lot, now less than 2.5:1 so now usable, but the rest of the bands still above 3:1 so not good to use, but the overall swr on the unusable bands has come down significantly, as a example, 15mtr was over 7:1 before the add on third leg, now it is closer to 4:1, which is a significant improvement.

Overall I would say it is a good addition to the windom, and I am reserving final judgement until I have put up a new windom antenna, as I have noticed a few issues with the existing antenna, such as water getting into the balun and the cables showing signs of ageing,

I personally think the results would be much better had it not been for the poor condition of my current windom, but I will update when I get a new one up.

My verdict is basicaly, apart from a slight increase in swr on 40mtr, on the other bands, it certainly made them no worse, and in most cases, showed significant improvement, so nothing to lose by adding it. Karl, M0KRL

 

[wavrider]

Karl,

I tore the shack apart looking for the 4:1 balun. I must have donated it to someone or built an antenna for someone and used it.



The OCF that I have played with worked best if suspended in the middle of the antenna roughly at 33' and install it as an inverted V. OF course the feed point will be off set but the ones I built worked best as mentioned.


Adding the 3rd leg I would treat it as an inverted V also off of the 6.76 meter leg.

It would look like a fan dipole but using the 6.67 m leg as a common for both legs.

Also the 13.52 leg needs to have 1 meter separation from the 3.68 leg.

I may wrap an air core 4:1 balun and try it just for kicks. Wish I could find my darn 4:1 current balun.

 

[M0KRL]

I would be very interested in other peoples experience with the design, unfortunatly at my QTH I have tight restricions as far as space is concerned, so much so that the short leg of my windom is connected to a neighbours chimney stack (very good neighbours), so a multiband antenna is my only HF option, and so far the windom, while being a compromise antenna, has served me well, so keep me updated with your results. Karl, M0KRL.