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Author Topic: 2 elements phased array  (Read 843 times)
F8DRA
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Posts: 29




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« on: December 06, 2012, 06:25:57 AM »

Good morning,
I use to have a 40M 2 elements vertical phased array antenna with a 1/4 waves spacing between the two monopoles.
Now, i'd lile to test the same antenna but with less space between the two verticals, i'm going to choose a 1/8 waves spaced vertical array, according to the ON4UN low band DXing and the ARRL antenna book, this option would give a better gain but smallest bandwith. The front to back ration should be better too.
I read that the phasing line must be 135° length but don't know how long must be the two feedlines in this case ?

If someone has already tested that kind of antenna ( the 1/8 wave spaced one ) i'll be very glad to know how this antenna work and how long must be the two feedlines.

Sorry for my english .... Huh

Best regards

F8DRA, Marc
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N4JTE
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Posts: 1147




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« Reply #1 on: December 06, 2012, 02:42:36 PM »

The best advice I can give you is to stick with 1/4 wl spacing using 84 degree phase lines and a 71 degree lag line for direction changing.
135 degree phasing is extremely tricky to achieve while matching phase and voltage in equal amounts at both antennas.
While in theory the 1/8 spacing and 135 has slightly better gain I stick with the quadrature, christman method and very happy with 24 db minimum front to back from 7160 to 7200 as verified daily with east and West dx stations along with stateside contacts.
Bob
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K3VAT
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Posts: 699




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« Reply #2 on: December 06, 2012, 03:17:47 PM »

The best advice I can give you is to stick with 1/4 wl spacing using 84 degree phase lines and a 71 degree lag line for direction changing.
135 degree phasing is extremely tricky to achieve while matching phase and voltage in equal amounts at both antennas.
While in theory the 1/8 spacing and 135 has slightly better gain I stick with the quadrature, christman method and very happy with 24 db minimum front to back from 7160 to 7200 as verified daily with east and West dx stations along with stateside contacts.   Bob

I agree with N4JTE's recommendation; 1/8 wave spacing can be very touchy.  Another point to especially consider when using 1/8 wave spacing is the typology of the radial field.  There should be a center-line connecting bus wire midway between the two elements electromechanically connecting all those radials sharing common typology.  This is also covered in ON4UN's book and there is a diagram to help you visualize the radial layout.  Non-symmetrical radial layouts or crisscrossing radials are discouraged. 

GL, 73, Rich, K3VAT
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F8DRA
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Posts: 29




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« Reply #3 on: December 07, 2012, 01:14:01 AM »

Thank you for all your recommendations, several friends of mine told me the same recommendations about the difficulty of adjusting a 1/8 spaced vertical array, according to few articles that i've read there is not a so big difference in  gain so i'm going to follow your ideas and opinions and keeping my first antenna configuration ( the 1/4 waves spaced ) .

Thank for your help  Wink


PS : if someone has already tested this 1/8 spaced vertical array, i'll be interested to know how this 2  elements work out !!!! and how long are the 2 feedlines and the phasing line too because in the last ON4UN edition, this antenna doesn't appear anymore Huh
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