Windom Antenna Adjustments - help please

[VK2XTC]

Hello,

I built a Windom antenna this weekend and was wondering if anyone has experience with this type of antenna ?

It's basically a 40 meter dipole fed at the 67% and 33% point. 4:1 Balun. SS wire and copper swages.
What is the process the adjust SWR, which end first and how to get it to resonate on multiple bands ?

40M is 1.35:1 @ 7.010 Mhz and and 1.15:1 @ 7.295 Mhz
20M is 1.2:1 through to 1.4 :1 at the top of the band

10M is high at 2.5:1 up to 3.5:1 at the top.
6M is again high at 3:1 flat.

Any suggestions on tuning one of these antennas ?
I tried shortening the thing by about 400mm (long leg, short leg both legs), and the difference in SWR was maybe .5. Not what I expected.
I have left the swages at the balun loose to enable me to adjust length if required.


Brian

VK2XTC

QF56oe

[VK4WDM]

Hi Brian

I have the same antenna. Mine was commercially made but it still required some tuning. Do you have an antenna analyzer or can you borrow one? It will make the tuning much easier because you will be able to see whether it it needs to be lengthened or shortened.

My first goal was to get the SWR to as close to 1:1 on 40m. That required VERY small (about 10mm) pruning steps from both sides. I could only manage to get it to 1:2 on 40m. It was the same on 20m and 15m without any more adjustments. On 10m is was 1:5 and a few more snips brought it to 1:3. I did not try to get it any lower because I can bring it to a 1:1 match using either the internal tuner in the TS-2000, or the outboard MFJ Versa Tuner which also makes it usable on 30, 17, and 12m.

No, its not a beam, but I am very impressed with mine which is only 6m high in the centre and 5m high at the ends. It has given me some really good contacts all over the world even on 10m where it seems to be a bit compromised, but as I said, I do need a tuner to make it happen on all bands.

73

Wayne VK4WDM

[VK2XTC]

Wayne,

Thanks, I made a Windom as I needed a multi band antenna and could only have one due limited in space.

As it turns out my carport (which was once a veranda some 100 years ago) is q bit longer than length of a 40 Meter dipole. (approx 22 meters).
So that plan is to mount it via some stand offs on pipe along the line of the gutter. Getting it as high as the neighbour will permit.

I was surprised at how flat the VSWR was, with very little difference across the band.

I tried making changes and still no real change in VSWR. Confused me.

Unfortunately I don't have a an antenna analyser, not sure if that's something you can rent somewhere.
I'm using an external VSWR meter as I have a TS-2000 and the meter on that is not great.

Do you have a vertical section on yours , or is it all horizontal , 67% 33% ratio ?
Vertical version has 37.8% // 62.2% with approx 10 feet to Line isolator.


Brian

VK2XTC

[VK5PL]

I would think you would need to take the same amount off each side to maintain the ratio between long & short.

[VK4WDM]

Hello again

I don't have a vertical section on mine and he short section is only about 2m above the roof. I worked into Africa on 10m with 100w of SSB and into eastern Canada on 40m with 30w of JT65 yesterday.

I am going to try shorting the feed line and feeding it against ground like a Marconi T to see if I can get it to load on 80m. I will post the results here.

I think it will do very well for you just as it is with the external tuner. Have fun

73

Wayne VK4WDM

[VK2AVR]

I gather you're talking about an OCF dipole and not a Windom. Windom antennas have a single-wire feedline, although it seems to be commonplace to call OCF's a Windom.. they are quite different in operation and if well constructed suffer none of the feedline radiation issues that the Windom does. I don't know why hams love to keep the Windom name going, it seems like if you call a giraffe an elephant for long enough the rest of the world will know what you're talking about??

You have 3 tuning paramaters for an OCF (broadly speaking):
1) Dipole impedance generally is influenced by height above ground. Lower dipoles have lower impedance. A typical OCF needs a 4:1 balun, an OCF at significant height needs a 6:1 balun. MUST be current balun or the feedline will radiate and the tuning will vary when you touch your radio.
2) Overall antenna length - this sets the frequency of the resonant points. At the ideal feedpoint for that frequency this should correspond with a nice SWR dip.
3) Feed point - this sets the R+jX impedance at the dip of each resonant point. This needs to be tuned for best compromise over the bands covered once the overall length is established.

One huge trick with OCFs is not to trim them at first in case you go too far. If you double back an element on itself by making a sharp 180 degree turn and wrapping the loose "tail" around the main element then it will effectively be shorter. You can then fiddle with the overall length and relative feedpoint as much as you like.

I find tuning OCFs to be far more intuitive with an antenna analyser. Especially one that shows you a graphical display like the Youkits FG-01. It took me 3 'trim' attempts and 10 minutes to get an OCF fed at the 17% point (1/6th distance) to give me low SWR on 40-20-15-10m. Having the SWR graphed tells you a) where the dip is in frequency and b) how good a dip it is. Changing the feedpoint changes the "goodness" compromise across each band.

On 10m you need to find out where the lowest SWR point is. If it's outside the band you may need an antenna analyser to spot it. However it seems like the SWR is increasing with frequency which means your antenna is fractionally too long at 10m. And I mean fractionally. Try reducing your elements by a few cm (5cm) each end and re-measure SWR. Otherwise, it may be that your impedance is reactive and you might get a better result by moving the feed point (making one end longer and the other end shorter by the same amount).

You have achieved great matching on 40m and 20m so make small changes so as not to upset what you've already got (and make notes of the current dimensions so you can fall back if you make things worse). Shortening the antenna to suit 10m will increase your SWR at the low end of 40m because when you shorten the antenna, it moves ALL resonant points upwards. Instead of shortening you may be able to move the feedpoint and find a better match. Anything under 1.5:1 is awesome. Anything under 2:1 is good enough (most radios start folding back at 1.5:1 but it is a minor foldback until about 3:1 and then your output power really takes a dive). Obsessing about the difference between 1.35:1 and 1.2:1 is a waste of time.

Forget about 6m for now, sometimes you can be lucky and have it work but it depends on luck, and your balun's performance at 50MHz. Baluns only have a limited frequency range they work on, you may be outside it. If you get 40,20,10 working on one antenna that's a victory in itself.

[VK4WDM]

"a giraffe an elephant for long enough the rest of the world will know what you're talking about??" But a giraffe IS an elephant but with a shorter neck and no spots.

Hi Geoff

That is a really good explanation!

73

Wayne VK4WDM

[VK2XTC]

Well I had some time today to read up on antenna fundermentals and discovered something interesting.

American articles on "OCF Dipoles" {see.. PC now !} use the formula of L= 468/F (Mhz)

e.g. 468/7.1 Mhz = 65.9154 Feet

However, I use the more scientific measure of a metric (rather than the length of some kings appendage who's name I don't know) and use L=300/F (Mhz) in meters.
e.g. 300/7.1 Mhz = 42.2535 Meters. (1/2 wavelength = 21.1267Meters)

Convert Feet to Meters and I get 20.0910139 metres. Theres a big difference there.

So I've made the antenna too long by a long way...
How did the Americans come up with the number 468 ? Is it some on timer ham figure or is there science to it.

Also, some people use 67% / 33% others use 37.8% / 62.2 % to get their feed point.

It seems that making antennas is more "magic" than science.

I'll never get this thing right if I cannot get the basics correct ......


Brian


A colleague has an Antenna Analyser that I may be able to borrow (he's trying to sell it to me at present) (VK5 Kit ??)

Lastly, Common Mode Currents. Seems I need an RF Choke for this antenna. Heading to eBay for some ferrite cores as Air Wound Balun (Coax) is not broadband enough, so articles say..

[VK2XTC]

Found it.

http://www.eham.net/articles/23802

Seems it a correction factor for a "Practical" antenna, rather than the figures derived from an antenna in free space.

See, there is an "Art" factor in there after all.

So what figures do you use ?




Brian

[VK4WDM]

Mine is commercially-built by W8AMZ. Dimensions for the 40-6m version: 66' long. 44' on the long side & 22' on the short side with a 4:1 balun rated to 2KW. I have two ferrite beads at the top of the feed line and one at the bottom. No evidence of common-mode problems.

73

Wayne VK4WDM

[VK2XTC]

Wayne,

I looked at those but they worked out to be $169 delivered (A$ - US$ movement changes that).
I had the insulators from years ago, and Stainless Steel wire and swages from another project with a shade sail that didn't go ahead.

I purchased the Tet-Emtron 4:1 balun kit as I also have a Bushcomm folded dipole and they are the same parts.
The Bushcomm folded dipole is just a little too long for my site here.

I'll start with the basics and get it working on 40M first, with the long / short leg lengths corrected to the "American version of a Half Wavelength" and take it from there.

I need the ferrite beads for the coax as the Cat control now fails every time I transmit due to excess RF in the shack.

Still, I actually enjoy stuffing around with this. I'm remembering what I liked about Amateur Radio all those years ago !.



Brian

[VK3ALB]

Hi Brian,

You can make your own balun using cores from Jaycar or you can buy Amidon cores from MiniKits in VK5. Don't discount the Jaycar cores, they will get you on the air with a minimum of fuss. Of course, you can also use them to make choke baluns and help tame those problems on your CAT cable.

Part numbers

Ferrite ring cores suitable for balun & choke construction - Jaycar LO1238
Ferrite sleeves used for 4:1 balun made from RG174 - Jaycar LF1260
Small ferrite sleeve (fits over RG58) - Jaycar LF1258
RG174 coax - Jaycar WB2018

If you want to learn more about baluns look around for texts by Jerry Sevick W2FMI. You can also download his book called Transmission Line Transformers Handbook

Here's Ron Bertrands article on the OCF dipole.

[VK4TI]

Hae you tried simply adding a multi turn choke under the antenna feedpoint ( ugly balun) usually works and can take up access coax

[VK4WDM]

I brought mine from a ham who had got it from the USA and then found he did not have enough room for it. At $70 it was a bargain, but I usually HB wire antennas because it is fun for a TAWAN like me Even though it was commercially-made it still required a bit of fine tuning.

"Ugly baluns" or "coax choke"? Maybe a case of calling elephants giraffes again but they do a good job. The only reason I did not use one on the OCFD is that the feed line I am a using is a tad short to make the turns, but there is no evidence of common-mode currents with the ferrite beads.

73

Wayne VK4WDM

[VK2XTC]

VK3ALB (Lou),

I made the 4:1 balun, but it was from a kit. (but you have to wind it , so more like an expensive shopping list )seems to work fine. But to be sure I'm going to disconnect the lengths of SS wire and put a 200 ohm , 10 watts resistor across it and measure it's response.
I'm on to the ferrite beads solution for the stray currents and have already purchased some from my local Jaycar store.
(why I'm on that, where do you buy good quality coax from nowadays ? the cheap stuff they sell is terrible quality.)

Thanks for the link to the article.

VK4TI, (?)

About to start construction. 7 Meters of RG58 on a 100mm PCV sewer , got both lying around. Hopefully won't be too Ugly.

The plan at present is, I'm going to build the choke on the PVC pipe with caps both ends and SO-239. It means I can move it later to the next antenna. And I don't have that much Coax spare in the primary run.
I'll also make a short lead of coax with ferrite beads over it then I can use both together to ensure no leakage.

I'm in Artarmon surrounded by 3 TV and FM Radio Transmission Towers, There is enough RF about to light a Fluro !
The more RF suppression I can achieve the better, I have S7 noise floor on 40 Meters.


Brian

[VK3ALB]

If you're happy to use RG58 I can recommend the Altronics W2230 offering. The braid has very good even coverage over the inner and the inner conductor is multi strand and seems to be of good quality. It stands up well to the elements, trampling, driving over it, packing and unpacking and doesn't seem affected by UV.

[VK3AIF]

Well I had some time today to read up on antenna fundermentals and discovered something interesting.

American articles on "OCF Dipoles" {see.. PC now !} use the formula of L= 468/F (Mhz)

e.g. 468/7.1 Mhz = 65.9154 Feet

However, I use the more scientific measure of a metric (rather than the length of some kings appendage who's name I don't know) and use L=300/F (Mhz) in meters.
e.g. 300/7.1 Mhz = 42.2535 Meters. (1/2 wavelength = 21.1267Meters)

Convert Feet to Meters and I get 20.0910139 metres. Theres a big difference there.

So I've made the antenna too long by a long way...
How did the Americans come up with the number 468 ? Is it some on timer ham figure or is there science to it.

Also, some people use 67% / 33% others use 37.8% / 62.2 % to get their feed point.

It seems that making antennas is more "magic" than science.

I'll never get this thing right if I cannot get the basics correct ......


Brian


A colleague has an Antenna Analyser that I may be able to borrow (he's trying to sell it to me at present) (VK5 Kit ??)

Lastly, Common Mode Currents. Seems I need an RF Choke for this antenna. Heading to eBay for some ferrite cores as Air Wound Balun (Coax) is not broadband enough, so articles say..

As I am led to believe the "468/freq Mhz = L feet" takes end effect into account which amounts to about 5%. The amount of end effect can vary depending on what other conducting material is near the ends of your antenna so some adjustment may be required. Where an antenna has multiples of a half wave length the end effect only plays a part on the outer most ends of the antenna so a piece of wire that resonates at say 7.1 Mhz would not resonate on exactly 14.2 but closer to 14.53Mhz so a compromise will have to be reached as far as where you will accept the resonances to be. To take it to the next multiple it will be around 21.99Mhz and so on. So consequently you will not get everything tuning up as you would like or where you would like it to.

Again, as I understand it the offset of the feed point is looking for a magic spot where all bands present the same impedance to the 4:1 or 6:1 balun and if you were to plot the current curves for the various band you will see this point. Because the feed line is not in the centre of the radiated field it does not have equal but opposite antenna currents imposed on it so therefore it will skew the radiation pattern somewhat and will also radiate and conduct antenna currents back along it and possibly into the shack unless you have an effective choke of some kind in the line preferably somewhere away from the strong field. Maybe bring the feed line straight down to ground level and place the choke there bring the feed along or even better, below the ground to the shack. You might also be better off starting with a fundamental frequency somewhere below 7.1 Mhz, even below 7Mhz and check each band as you make adjustments.

I myself use a W3DZZ antenna for a multi band HF antenna as it is symmetrical it does not have the feed line radiation but it still has the end effect problem operating on its harmonics. It is actually slightly shorter than the comparable OCFD and not too hard to make work so try one of those? I feed mine with 50 Ohm line through a 1:1 balun and if you are contemplating making one I would advise steering away from the ones using coaxial traps as they are pretty lossy in that design at least.

Please correct me if I am wrong on any or all of this ay?

[VK4WDM]

I find it fascinating that even with all the complex technology available to us, many hams still have great fun messing around with pieces of wire.

My XYL says that all the nursing home will need to do to keep me happy is give me a piece of wire to play with.

73

Wayne VK4WDM

[VK3XL]

I find it fascinating that even with all the complex technology available to us, many hams still have great fun messing around with pieces of wire.

My XYL says that all the nursing home will need to do to keep me happy is give me a piece of wire to play with.

73

Wayne VK4WDM

Me too. I have recently put up a full wave loop for 80 meters and initially fed it with some TV 300 ohm ribbon. Encouraged by how much better signal to noise I was getting compared to my 160 meter doublet fed with home brew open wire line, I replaced the 300 ohm line on the loop with some 600 ohm open wire line on the weekend.
I then did a quick comparison between the doublet and the loop and found that the loop out performs the doublet with respect to signal to noise on all bands except 160 meters (as you would expect).

Keep playing with your bits of wire.

[VK3XL]

Brian many years ago I did some experimenting with a off centre fed dipole and wrote an article for a radio club I am involved with. Unfortunately the club website is down at the moment but I found it using the way back machine.
You may find some of the info useful with your current tuning issues. I found that the balun design did have an effect. There are a couple of different designs around for 4:1 Baluns and it may be worth trying a couple of different ones to see which suits your particular circumstances.

Here is a link to the article I wrote.
http://web.archive.org/web/200605101342 ... domhtm.htm

I still have the antenna in the air, but predominantly only use it on 40 and 80 as a backup antenna.

Good luck with getting it working how you want.

p.s I have moved to 450 ohm open wire line on a 160m half wave doublet 4:1 balun outside the shack and about 2 meters of coax into the shack. This is coupled to a TS830s via its matching AT230 "tuner". I find this is more versatile arrangement, but still mostly used on 160, 80 and 40. I recently added the 80 meter full wave loop to the mix as in my post above and am still to make up my mind which I prefer.