Sirio SY27-4 Beam Install

[vkrules]

No.The next director has to be spaced way out to get worth while result. Would have liked to go 8 or 9 meter boom and change all the spacing but that would have required changing the matching network and purchasing more materials.
I was feeling lazy and went with the materials I had on hand.
Was after minimum work and better front to back , previously had already maximized for 28.3 . I went with the model I had used to get what I wanted for 10 meters then added a director.Modeling with yagi cad I found the spacing and length that provided what I wanted without changing the resonance or radiation resistance much . Swept it after modification with the ant analyzer. Then using the analyzer as a rf source 100 meters away took rf readings and plotted a polar graph . The change in pattern was obvious with a much cleaner pattern.I'm very pleased with the results.

 

[vkrules]

I also added 12 cm to director 2 .

 

[firerunner]

Vk thats very interesting, I would like to see a picture of your antenna now. I would have thought that one would just space the extra director the same or just a little more that the previous one but i'm just learning ( not judging what you did). One thing I didn't mention on my antenna, I saw a recommendation from somewhere about adding dowels to the elements to help strengthen them so I also did this. They were light and didn't add a lot of weight.

 

[mb91w126]

While it was down I added 3 meters of boom and another director, now it really rocks!

how does one calculate director distance and size

 

[vkrules]

That math is beyond me .I used a design program.
Size and location of the parasitic element is everything and effects all the parameters of the antenna, it is possible to add an element and degrade performance.
Changing the length of one element can change the required length of the other elements.
So there is no single "right size"it depends on the other elements. Have a play with one of the design programs that are available , it will show you whats going on.
The dowel reinforcing is a good idea on this ant

 

[Marconi]

how does one calculate director distance and size

I think the element length beyond the first director tends to make little difference in my quad models. My yagi models may be a bit different however, but I have not studied that idea in the yagi design.

In my real world experience I believe I found with the yagi as I get away from a somewhat better balanced spacing designs, like the Moonraker spacing for example, I found otherwise that all of the modified dimensions to be far more sensitive and harder to get the same or better performance...compared to the more traditional well balanced method of multelement spacing designs. So, I prefer not to use the optimized design ideas.

I know this is not much help, but maybe you can find some ratios in the ARRL handbook. I refer to page 153, Table 4-11 for some starting point ratios and you can figure the math from there.

 

[vkrules]

Yes some designs can get to sensitive to reproduce real world . I'm always wary of any model that changes dramatically when you change the dimensions 10mm or so .I like to error on the long side for director spacing and short on director length.Short spaced arrays with the directors close to the resonance of the driven element tend to be too sensitive.
The old .2 of a wavelength element spacing will still work if you don't have a design program. And lets be honest good gain is easy to get . The trick is to maximize gain and front to back ratio without lowering the feed point impedance and bandwidth to much.Cebick Lawson and Lyngby all produced different designs yet they all worked.

 

[vkrules]

Quads maybe a little different .Making the directors of my yagi the same length as the first director produced a loss in the front to back ratio of 18 db and dropped the feed impedance to 6.5 ohm.
It did however show an improvement in gain of 1 db.
Real world I can't measure an improvement of 1db but a change of 18db in the f to b is obvious .

 

[Marconi]

Yes some designs can get to sensitive to reproduce real world . I'm always wary of any model that changes dramatically when you change the dimensions 10mm or so .I like to error on the long side for director spacing and short on director length.Short spaced arrays with the directors close to the resonance of the driven element tend to be too sensitive.
The old .2 of a wavelength element spacing will still work if you don't have a design program. And lets be honest good gain is easy to get . The trick is to maximize gain and front to back ratio without lowering the feed point impedance and bandwidth to much.Cebick Lawson and Lyngby all produced different designs yet they all worked.

Thanks for your thoughts VK. In my real world testing I've found that just about any beam, within reason will work.

I've setup a beam that responded for me just like an omni antenna, but it did show gain over my vertical omnis.

I've also setup a single polarity horizontal Moonracker that had the driven element at the end. It only had directors...no reflector. I saw it work, but it was only as good as the regular MR'r beam for me. The rejection, close in was exceptional however...and I never was able to explain that. It could have been a fluke, but I tested it over a month and it was very consistent at reducing signals by up to 9S units, and that really surprised me.

Here is a model that I was just working on recently at the request of another member. The Signal Engineering Lightning L4+ which I think is optimized in the last director element vs their original Lightning 4.

You will note that the factory model has a bit more gain, but my model with spacing set at 60" between the elements is a better compromize that shows much better rejection.

 

[Marconi]

Quads maybe a little different .Making the directors of my yagi the same length as the first director produced a loss in the front to back ratio of 18 db and dropped the feed impedance to 6.5 ohm.
It did however show an improvement in gain of 1 db.
Real world I can't measure an improvement of 1db but a change of 18db in the f to b is obvious .

VK. I agree that most of the iterations we might make within reason on a MultiElement beam mostly effects the match and the rejection...rather than the gain. This is probably why my omni beam noted above showed me a nice gain...as best I could tell with RX signals...just by using my radio.

 

[Matt5527]

Nice thread everyone. Here is a free Yagi design program I found. I'm trying to build a 5 or 6 element Yagi for 10m voice so I will probably purchase the SY27-4 and then modify the boom and number of directors to give me some additional gain. de KD8NCP

http://www.k7mem.com/Electronic_Notebook/antennas/yagi_vhf.html

 

[vkrules]

Her is an other program.http://www.yagicad.com/

 

[Marconi]

Hey Robb, I want to model your beam, do you have the specific dimensions for spacing and element length for your SY27 - 4? The manual is not specific.

 

[Robb]

Sorry Marconi, I just slapped it together, set the gamma, and threw it up on a push-up pole and have been using it every day since then. Never thought about dissecting it. Found this diagram, but it's measured in millimeters . . .

 

[Marconi]

View attachment 14706 Sorry Marconi, I just slapped it together, set the gamma, and threw it up on a push-up pole and have been using it every day since then. Never thought about dissecting it. Found this diagram, but it's measured in millimeters . . .

That is Ok Robb. I'll just guess at the lengths for a,b,c,d. I think they are not adjustable...as I understand it they come fixed length, right?

The spacing design looks very well balanced if the diagram is close to scale.