Pruning a 440 antenna

[SCPD]

I have several plans for 22 and 33 element beams for 440, out of the ARRL Antenna Book.
My question stems from a discussion I had at a recent ham club meeting.
Can I take plans for a 22 element 440 beam, and make just a 7 element out of it, by just using 5 directors instead of 20, without changing the original spacing or length of the remaining elements?

 

[tyytor]

i would think yes, it would depend on the factors that made up the antenna, metal boom...ect
i think that it would be easier to just go from these (links) if you are not going to do EME, EVE modes
you would loose db gain hope they help lots of building ideas


links;
Free Yagi Antenna Designs for Ham Radio
Amateur Radio Antenna Projects
http://www.k7mem.150m.com/Electronic_Notebook/antennas/yagi_vhf.html

 

[W6KRU]

I have several plans for 22 and 33 element beams for 440, out of the ARRL Antenna Book.
My question stems from a discussion I had at a recent ham club meeting.
Can I take plans for a 22 element 440 beam, and make just a 7 element out of it, by just using 5 directors instead of 20, without changing the original spacing or length of the remaining elements?

I don't think that would work very well at all. There are plenty of yagi calculators on the web. Here is a pretty good one. If you don't like it, google for more.

Martin E. Meserve - K7MEM - VHF/UHF Yagi Antenna Design

 

[Fast1eddie]

Martin, very nice site. I've bookmarked it. Many thanks!

 

[SCPD]

Thanks for all the help. I'm perusing the links. Thanks again

 

[kb2vxa]

The rule of thumb provided it's a true Yagi is all the directors are of the same length and spacing so just take it from there. You don't need a calculator, only a hacksaw.

 

[kb0nly]

The rule of thumb provided it's a true Yagi is all the directors are of the same length and spacing so just take it from there. You don't need a calculator, only a hacksaw.

My thoughts exactly.

I have taken designs for UHF that were 20+ elements and built a 10-11 element yagi using the dimensions for the first half of it, worked just fine.

 

[k8wha]

I have several plans for 22 and 33 element beams for 440, out of the ARRL Antenna Book.
My question stems from a discussion I had at a recent ham club meeting.
Can I take plans for a 22 element 440 beam, and make just a 7 element out of it, by just using 5 directors instead of 20, without changing the original spacing or length of the remaining elements?

Theroetically the answer is yes.. the reality of the situation is not exactly... all those director elements have an interaction and the spacing makes a difference in the overall gain of the antenna. Going down to five disrectors with out changing the spacing slightly will not yeaild an optimized forward gain as well as Front to back ratio. Also the horozontal lobes are affected by wave length height. You may be better off just keeping the 22 elements and adjusting the height to pull the lobe angle higher since you will end up with reduced gain with 7 vs 22 or 33 elemnt yagi.

Something to think about...

73's


Dick

 

[SCPD]

I made a 5 element

Theroetically the answer is yes.. the reality of the situation is not exactly... all those director elements have an interaction and the spacing makes a difference in the overall gain of the antenna. Going down to five disrectors with out changing the spacing slightly will not yeaild an optimized forward gain as well as Front to back ratio. Also the horozontal lobes are affected by wave length height. You may be better off just keeping the 22 elements and adjusting the height to pull the lobe angle higher since you will end up with reduced gain with 7 vs 22 or 33 elemnt yagi.

Something to think about...

73's


Dick

Thanks for the help. I ended up making a 5 element from the links posted earlier. I had to go with a "shorty" because the antenna was going to have to be end mounted off a mast. I didn't need a whole lot of gain anyway, and all 440 machines in Metro Detroit are due north for me.