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15FB269 Profile
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New Kid On The Block

Registered: 09-2012
Posts: 1
Karma: 0 (+0/-0)
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4 Element Yagi for 11m tuning question


I would like to have a go at building a 4 element yagi for 11m. the dimensions are as follows:

Reflector 546.74cms
Driven: 517.85cm
Director 1: 509.27cm
Director 2: 473.4cm
Boom: 410.0cm total element spacing 400.05cm
spacing between elements
ref to driven: 105.73
driven to Dir1: 105.73
Dir1 to Dir2: 188.6

My question is about tuning. as I will not be using a gamma match is it as simple as just tuning the driven element just the same as a dipole? AND as its not exactly the most easy antenna to keep lowering and raising into position to check and re check how critical does the matching have to be? what i mean is lets say I set everything up as per the computer model and its still a little out say due to surroundings, are the losses large if I use an auto tuner just to trim up?

Last edited by 15FB269, 1/Oct/2012, 10:00 pm
1/Oct/2012, 9:52 pm Link to this post Send Email to 15FB269   Send PM to 15FB269 Blog
 
yamanx1 Profile
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Registered: 09-2007
Location: In a world of my own
Posts: 4894
Karma: 40 (+41/-1)
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Re: 4 Element Yagi for 11m tuning question


Yes tune it as if it was a dipole, the VSWR may change depending on surroundings, but try it. In my experience, unless the surrounds are severe there is little difference. Try not to use a matcher, but 1:1.5 is acceptable emoticon

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By all means think yourself big, but never think others small.... R.F.Scott
2/Oct/2012, 6:24 pm Link to this post Send Email to yamanx1   Send PM to yamanx1
 
madmark1 Profile
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Accomplished DX-er

Registered: 10-2009
Location: Abertillery
Posts: 454
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Re: 4 Element Yagi for 11m tuning question


You will have to use some sort of matching device... why.... well a dipole on its own will have a impedance of around 50 to 80 ohms depending on how high above ground it is, Trimming the dipole will allow you to get a good match to your 50 ohms coax and radio.

When you add elements such as the case for a yagi, The elements will effect the dipole element and this will have the effect of reducing the impedance so your tuned dipole wont be tuned anymore, with only one extra element such as just adding a reflector you may gey away with it BUt the more elements you add the more they effect the impedance, Normally a yagi with 4 elements will have a very low impedance, Somewhere around 8 or 10 ohms, This impedance wont matvh to your 50 ohms coax and radio so you will need some sort of matching device to match the dipole to your coax... a gamma rod will do it.. its easy to make. loads of info on-line..


Mark

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9/Oct/2012, 8:18 pm Link to this post Send Email to madmark1   Send PM to madmark1 Blog
 
yamanx1 Profile
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Head Honcho

Registered: 09-2007
Location: In a world of my own
Posts: 4894
Karma: 40 (+41/-1)
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Re: 4 Element Yagi for 11m tuning question


If you're using a gamma match, I have a spare you can have emoticon

---

By all means think yourself big, but never think others small.... R.F.Scott
19/Oct/2012, 3:09 pm Link to this post Send Email to yamanx1   Send PM to yamanx1
 


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