Friday, July 29, 2011

Eight Bands On One Coax - The Windom Antenna

Eight Bands On One Coax - The Windom Antenna
I Need A New Antenna
After trying the usual antennas that would fit in my limited space back yard, which is located in one of those wonderful Ken & Barbie subdivisions, I decided I needed to maximize the number of bands that would work on one coax. I tried my Butternut vertical, but even with a bunch of radials it played like a ground mounted dummy load - didn't work near as well as it did in Guam when it was surrounded by ocean. Dipoles were out of the question, because there wasn't enuff room for seven or eight different antennas and it didn't make sense to feed the squirrels that much coax.
Expand or Start Over?
Last summer I put up a triband delta loop - which seemed to play OK, nothing spectacular - but it was only for three bands, 10-15-20 meters. Fed with 1/4 wave 75 ohm stubs to a remote antenna switch, it resulted in only one coax into the shack, but adding bands would result in only a couple more WARC bands (no room for a 40 meter loop). And navigating it up and down while trying to keep the individual loops spaced correctly and not tangled was a time consuming job.
Back in my novice days I'd been the G5RV route, and the multiple dipoles on the same feedline route, and the results were dismal at best, so I didn't want to bother with those again. I needed a new antenna, one I'd never tried before.....
Antenna Hunting We Go!
The Internet is a wonderful place. You can find just about anything you want to find, it you look hard enuff. So after a few nites of hunting around in Google, I had come up with a few antennas that looked like they were worth investigating.
Requirements for my new antenna were simple: It had to have as many bands as possible on one coax. It had to be something I could BUILD myself (even though I'm getting really lazy in my old age, I still can't force myself to BUY a wire antenna - if I get to the point where the only option left is to buy wires from Gordon West, then I think it's time to hang up ham radio forever). It had to fit in my back yard (140 feet wide at the widest point and full of nasty short scrub oak trees).
One of the antennas I found was the Windom. A "true" Windom, from what I've read, is an off center feed dipole fed with a single wire feed line. I have a tuner, but experience has told me that RFI burns your lips, so never mind that idea. But an off center feed dipole fed with coax didn't sound bad. In my search I happened to find that one of my friends, VE1DX, had a Windom up at his QTH, so I discussed the idea with him. He seemed to like his (a commercial version made by a Canadian company that is no longer in business), and also sent me the paperwork and information that came with his antenna.
I found several "formulas" on the Internet to design Windoms, but they conflicted each other (by feet, not inches) so I decided to go with the dimensions used in the commercial version. A quick analysis of a Windom will show that it's the same length as a half wave dipole on the lowest frequency desired. But you'll find variances in recommendations for where the feed point should be. And nobody seems to know WHY it works on other bands, so you won't find much discussion of that subject at all. When this antenna makes it up to it's final resting place (twice as high as it is now), I may try fooling with some formulas/different feed points to see if I can improve the SWR on some or all of the bands.
Don't Get Your Hopes Up
To be perfectly honest, I wasn't expecting the Windom to work very well. You can't base how well an antenna works on what other hams say, or base how well it works on how much Deeee-X they claimed to have worked on it. Experience has also taught me that I can work 100 DXCC countries using a chain link fence for an antenna, and that doesn't make it a good antenna. Previous experiences with all band wonder wires had always been a flop.
Because I didn't have much faith in this one wire/all band wonder antenna, I didn't run out and buy a mile of stainless steel copper clad whoppie wire or the best balun I could find. I opted for a $20 balun (mistake, keep reading) and a roll of wire from the local hardware store.
The Installation
Three weeks worth of procrastinating got me down to the day that the Florida QSO Party started, a Saturday morning, so installation time was now or never. First try at hanging the Windom revealed that my favorite tree limb was about 10 feet too close to one end of the back yard and the antenna wouldn't fit. But after selecting a new tree, and some careful pruning (about 2 hours worth) with a ladder and a chain saw, the Windom was flying and ready to play. Wasn't up very high - 25 feet in the middle, 25 feet on the long end, 15 feet on the short end - but a quick check seemed to indicate it could hear pretty well and I was AMAZED to find that most signals on 20 meters were 2 or 3 S units LOUDER than my delta loop. Yes, I know. Wire antennas don't usually have 18 db gain more than other wire antennas. But what works in the book doesn't always work in the tree.... After a quick shower, I was ready to give it the Contest Test.
The antenna, as originally installed, had two wires (the top two in the image below). In this configuration, the Windom is advertised to work on all bands but NOT on 15 meters. But it heard GREAT on 15 meters, and I have a tuner, so a little SWR's not a problem, right? Wrong. Most Baluns that I saw advertised on the Internet warn about power limits. They are rated at whatever limit on SSB - and generally tell you to forget about AM and RTTY. But I figured that a Balun that's rated at 1KW on SSB should play fine with 100 watts on CW, even with a little SWR, right? Wrong. The antenna loaded up fine on 15 meters with the tuner, but after about 15 minutes of CW operation I noticed the SWR meter going nuts, and retuning wouldn't work. Whoppie. Now we've melted the 1KW Balun with 100 watts, and the contest is over. Not so. After about 10 or 15 minutes, the Balun cooled off again and I was back in business, but staying away from 15 meters.
I remembered seeing an old 40 meter dipole out in the garage, which was just about the right length for the additional two wires that were advertised to make 15 meters one of "ALL" the bands again, so a quick trip to the back yard with a tape measure, a ball of string, and the old 40 meter dipole produced the second set of necessary wires on the feedpoint to enable 15 (and supposedly 30) meter operation. Here's the final configuration:
It doesn't take a brain surgeon to figure out that since the feed point of the antenna is only 25 feet high, the ends of the two shorter wires are a lot closer to the ground than what they probably should be - maybe 2 feet higher than my six foot fence. Which may account for the high SWR on 30 meters. But with the addition of the second set of wires, 15 had become very usable, and the SWR on 15 and 20 was low enuff so I could pop back and forth between those two bands without even bothering with the tuner.
The antenna is obviously too low, but even at this height it's very usable on all bands but 30 meters. SWR on the bands as it's installed now:
3.800 - 1.5:1
7.000 - 2.2:1
10.125 - 3.4:1
14.000 - 1.9:1
18.110 - 1.5:1
21.100 - 1.5:1
24.900 - 1.4:1
28.500 - 2.1:1
The Windom works well enuff that the delta loops are now in the garage and after we get some trees removed from the back yard this summer, the antenna will go up on the top of a 35' mast, which I think may resolve the 30 meter problem. I've purchased a much better 4:1 Balun, which will alleviate the saturation problem. Moral to the Balun story is that if the SWR is high, don't use a tuner on the band it's high on. I've heard saturation stories from a couple other hams. If you are going to buy a Balun, I'd recommend a good one, not the $20 model.
On a side note, the antenna seems to hear pretty well on 160 meters, but I haven't tried transmitting on that band. Performance has been great - the only RFI problem I have is on 40 meters, and the only thing it seems to get into are computer speakers, which isn't much of a problem at all. TV, telephones, stereos, and the neighbors aren't complaining at all. I'm sure the antenna doesn't work as good as monobanders, but in a limited space situation, where lots of bands on one coax are a plus, I think the Windom is a great choice.
Yes, Virginia, I've been werkin' sum Deee-X. I werked YI just last nite on 20 meter CW, first call, 100 watts. Check my logs - everything starting 24 April 2004 was on the Windom - it's the only HF antenna I have up....
The Windom at VE1DX is up a little higher than mine is, but doesn't include the extra two wires for 15/30 meters. Paul has detailed SWR curves of his antenna on his web site on this page.

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