OWA Element Spacing

[Marconi]

Captain Kilowatt, I have been checking out and modeling the OWA design ideas you noted in Spongbob's thread.

I built your model using the basic Eznec5 and got a little bit more gain than Henry suggested. Without a working frequency I took a guess and used the middle of the band at 52.25 mhz. The match was not so good as I expected, due to your use of a hairpin match, (edit) which I did not add a hairpin to my model. The front to back was also worse than Henry's >20 dbi suggestion.

I modeled a few OWA 6 meter beam models off of the Internet without much success. So, I went back to G0KSC's website and used the dimensions for a direct fed 6 M 6 element OWA model, where Justin used Eznec Pro/4. My basic Eznec model came out very near perfect as compared to his model. So, I think my models below are pretty close...even using this older, not professional version of Eznec.

From the looks of your model below the gain and angle are good, but the F/B does not fair so well compared to my version of G0KSC's 6M 6 element model in Free Space or at 30' feet over real Earth.

The first two models are my Free Space and over Real Earth models of CK's 6 meter 6 element beam using his dimensions at 52.25 mhz. I did not included details for the SWR chart and bandwidth, because the match is bad not using a matching system. I also added the wires displays for both models. The AG ratios are good for all models. The boom on CK's model is connected directly to the antenna elements and the driven element is directly center fed. The currents report on the boom show to be very low however.

The second two models shown are G0KSC's dimensions and my Free Space and over Real Earth models of his 6 Meter 6 element OWA design at 50.15 mhz as noted on his website and attached below.

Note: my G0KSC's model uses a 3" isolated boom to element setup. I did this to make my antenna adjustments easier to manage. I have not compared Justin's model with the boom connected directly to the elements.

Link to G0KSC's Website: http://www.g0ksc.co.uk/50mhz-owa-yagis/6el-6-1m-boom-owa.html

 

[Captain Kilowatt]

Thanks for the info Eddie. My antenna is tuned for the bottom of the band around 50.200 MHz. As I mentioned in the thread the dimensions I presented may be a little off due to tweaking . The hairpin should not contribute to a poor match and in fact the match is very good at 50.125 MHz. I do not recall he exact impedance at the moment but an antenna analyzer was used and not just an SWR meter. The SWR rises sharply above 52.5 MHz however. On-air performance has been great and the F/B and F/S seems better than what your numbers indicate. It is hanging on the back side of the shop right now but is to go up sometime in the next month or so. I will take more accurate measurements at the time and present them here again.

 

[Marconi]

The hairpin should not contribute to a poor match and in fact the match is very good at 50.125 MHz.

My model did not include a matching device CK, so the match shown is bad at 4.336 SWR in the attached source data report. So, I did not include the SWR bandwidth curve report that could show us the broadband benefit that a OWA design should produce. I did not mean to suggest what you post above, in fact I agree with you on that point.

Justin's model produces a very good direct feed match with a very low SWR among other benefits, so I included the bandwidth SWR curve in his models. All I can claim about my model of your 6 meter beam is...I think I got all of your dimensions right.

Note: You also used taper and I can't model using that feature. So, like I said earlier...my model might not be of any use to you. Maybe Henry will find some time to do your model with matching and taper before you raise it up again.

I did this modeling, because I wanted to see if I could duplicate results that somebody with good credits, using Eznec, might generated. I was also trying to make a model showing all of the benefit features the OWA design indicates are possible...and doing it when using the non-professional basic Eznec software vs. the Eznec Pro/4 version...as in this case.

 

[BJ radionut]

CK: I guess I missed the post where your original info is listed.
I am interested in this beam...Your using a 30 ft.boom for how many elements?
The Hairpin matching (Homebrew?)...anyway I would like the specs...and maybe a few pics (if you have them) thinking about a build before the "snow" fly's and would be interested in your construction.
CK, I worked up your way the other day on 6m (VE9) area to couple stations.
Marconi what do you have modeled?...I would also be interested to see some info on a 6m beam with about a 20 ft. boom with Center frequency of 50.150 MHz with max gain at that point...F/B is not a factor, looking for forward gain and minimum beam width (?)
Thanks for your time...Same with you Marconi.
All the Best
Gary

 

[Captain Kilowatt]

My model did not include a matching device CK, so the match shown is bad at 4.336 SWR in the attached source data report. So, I did not include the SWR bandwidth curve report that could show us the broadband benefit that a OWA design should produce. I did not mean to suggest what you post above, in fact I agree with you on that point.

OK I guess I misunderstood your comment about the hairpin I used versus the SWR. That 4.3:1 SWR would transform rather nicely with the 4:1 balun.

Justin's model produces a very good direct feed match with a very low SWR among other benefits, so I included the bandwidth SWR curve in his models. All I can claim about my model of your 6 meter beam is...I think I got all of your dimensions right.

Note: You also used taper and I can't model using that feature. So, like I said earlier...my model might not be of any use to you. Maybe Henry will find some time to do your model with matching and taper before you raise it up again.

I did this modeling, because I wanted to see if I could duplicate results that somebody with good credits, using Eznec, might generated. I was also trying to make a model showing all of the benefit features the OWA design indicates are possible...and doing it when using the non-professional basic Eznec software vs. the Eznec Pro/4 version...as in this case.

I didn't really want to go with direct feed as I wanted the antenna to be DC grounded and the hairpin offered that.

 

[Captain Kilowatt]

CK: I guess I missed the post where your original info is listed.
I am interested in this beam...Your using a 30 ft.boom for how many elements?
The Hairpin matching (Homebrew?)...anyway I would like the specs...and maybe a few pics (if you have them) thinking about a build before the "snow" fly's and would be interested in your construction.
CK, I worked up your way the other day on 6m (VE9) area to couple stations.
Marconi what do you have modeled?...I would also be interested to see some info on a 6m beam with about a 20 ft. boom with Center frequency of 50.150 MHz with max gain at that point...F/B is not a factor, looking for forward gain and minimum beam width (?)
Thanks for your time...Same with you Marconi.
All the Best
Gary

Hi Gary. The antenna has six elements on a 17 foot boom. Below are the approximate final dimensions as I may have changed things slightly since then. The hairpin aka Beta match is simply a piece of stainless steel filler rod used in welding. The antenna had a former life as a Wilson Shooting Star 11m antenna and I was able to use the original element to boom clamps with muffler style U-bolt clamps.

Feedline and balun attachment point. Driven element is insulated from the boom with Plexiglass. The center of the element is fiberglass rod.

Half wave coaxial balun attached. Feedline connects to the middle SO-239 connector.

Old picture showing it at 42 feet on the old tower. Notice the wrecked A3 tribander below it with only one element left attached to the boom. Since this antenna was originally an 11m antenna and shortened to 6m it makes for a VERY heavy duty antenna.

 

[The DB]

I modeled the antenna as well, I mounted it 36 feet up because, well, that is where I mount most of my antennas... Like Eddie's my model has no matching system, but the rest of the description is as stated in CK's image. AGT comes out to a 1.0, which is perfect.

Here is the gain and front to back and rear numbers over the 6 meter frequency range...

That drop in gain at 53 MHz, changing the driven element length does not change that frequency much, so I would put forth that if you want to use the upper portion of the band you would also have to adjust at least some if not all of the element lengths...


The DB

 

[Captain Kilowatt]

Probably the ONLY reason I would want to use the higher end of the band would be to use a repeater about 15-20 miles away but I am not even sure it is still on the air since I never listen up there. LOL

 

[Marconi]

Marconi what do you have modeled?...I would also be interested to see some info on a 6m beam with about a 20 ft. boom with Center frequency of 50.150 MHz with max gain at that point...F/B is not a factor, looking for forward gain and minimum beam width (?)
Thanks for your time...Same with you Marconi.
All the Best
Gary

BJ, if you check the 2nd image I posted in my original post above, "G0KSC 6m yagi 50.15 mhz" and check the dimensions I posted on the 1st page, you will see one of Justin's models with a 20' foot boom, which he claims is about the optimum length boom for his OWA design.

The model shows very good gain at a low angle, almost perfect direct fed match, and pretty good rejecton from the rear.

If you prefer a beam with the features like CK posted, then try his design. He gives us his dimensions and the reason why he prefers to use the hairpin match and the balun.

I also did a model of CK's antenna, but I was not able to add the matcher or the balun...however it is fair for some to say...the model can be said to show dubious results in this regard, and due to these omissions.

The originator of this OWA design suggest, if folks want a different mix in their beam project...to contact him and he can help with the dimensions and design. I left the link to his website above.

Keep us posted on your progress.