| Author |
Message |
    
matt r pratt
| | Posted on Sunday, July 22, 2001 - 7:34 pm: | 
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I am quite sure that with the correct instruction building a 3 element yagi beam for 27mhz would be relatively simple however I have been unable to find plans for one anywhere if I just knew the element lengths and spacing in between I could construct one any input would be greatly appreciated thank you |
707
| | Posted on Sunday, July 22, 2001 - 9:48 pm: |
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check out the antenna links at my website http://www.dxring.net You will find many different plans and calculators to get you started. |
Tech181 (Tech181)
| | Posted on Monday, July 23, 2001 - 12:05 am: |
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707,
Cool! Can't wait to check it out. I have the formulas down for the element length and spacing but was having a hard time finding the right materials!
Steve
181 |
Anonymous
| | Posted on Monday, July 23, 2001 - 9:00 pm: |
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This website was nice but there was only instruction for quad if someone would just give me boom length
driven element length
reflector length
director length
spacing between elements
If the If the driven element is actualy two pieces how far apart do the pieces need to be apart and does this spacing in between add/reduce element length . Do you need a gamma match for 3 element yagi ? what size metal can you use and where to get it? my center frequency would be about 27.205 if someone could calculate for me.thanks |
707
| | Posted on Tuesday, July 24, 2001 - 12:13 am: |
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Gamma matches are used when constructing a yagi antenna where the driven element is solid, bolted to the boom. Here is a link to a description for a type of gamma match using a fixed capacitor. A variable cap could also be used.
http://members.tripod.com/~cb_antennas/gamma.jpg
You can build a gamma match in several different ways, including the classic sliding matcher found on most commercial beams. The advantage to those is price and durability compared to investing in a heavy duty 100pf air variable cap, which is much easier to tune, but is susceptible to damage from hail, bug goop, etc., unless you mount it in a plastic enclosure.
Here is a page with calculators to determine element length:
http://members.home.net/ac3l/antenna.htm
You may choose to use a direct connect type of feed. This is when you actually split the driven element into two separate sides. In that case here is a link to show you how to do that for 2, 6 and 10 meters. You will need to do a little calculation for 11m.
http://members.home.net/ac3l/antlegn.htm
If you will carefully read through this page:
http://members.tripod.com/~cb_antennas/yagi.html
you will find all the info you need.
Research is part of the fun in building your own antenna. If you don't want to do a little research and calculation, then you might as well just buy a simple 3 element beam, which will cost about the same as buying your own aluminum stock, brackets, bolts, time spent fabricating, etc. and will already be designed to withstand Mother Natures buffeting. It's one thing to build your own yagi, and another thing altogether to have it last past one good springtime windy thunderstorm.
I stop building my own yagi antennas at 6m, mainly because I've found that going any any larger than that, the materials cost shoots past the satisfaction factor, unless you have the stuff on hand, which I generally don't. |
Anonymous
| | Posted on Tuesday, July 24, 2001 - 6:12 pm: |
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Thankyou very much for the info it was very helpful towards construction for my yagi however im thinking of buying one now skip all the hassle thanks alot everyone |
707
| | Posted on Tuesday, July 24, 2001 - 11:31 pm: |
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Ive seen at least one 3 element 11m beam built using a piece of aluminum tubing from a pool skimmer,and bunch of 102" fiberglass whips. It looked kind of crazy in the wind, but worked ok. |
Josuha
| | Posted on Thursday, July 26, 2001 - 11:07 am: |
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A 3 Yagi uses a half wave dipole a using director (front element) and a reflector (rear element) The dipole is the driven element. The driven element is calculated by the follwing formula 468 divided by frequency. (example: 468 divided by 27.195)
I use a program called "Yagimax 311" to calculate distance of the elements and boom length to get the gain and forward to back ratio I want. It can be found on the net on Yahoo using "yagimax" as the search engine inquiry. 73's |
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