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Cross Yagi with folded dipoles.



Hi all,
I have just changed antenne to a 2x19 element Tonna
cross yagi for 70 cm.
Up to now I have used first a 16 turn helix, model G3RUH, then
a linear 19 element Tonna.
The Tonna 2x19 have folded dipoles which seems to give a small
problem if they are not exactly at resonance.
I have made a left hand - right hand switch which is in line
as well.

It seems that the rear driven element changes impedance compared
to the forward driven dipole.
First I had trouble getting the VSWR down. It is 1.7 now.
Second I was not convinced that the pattern is really circular.
This was when listening to different satellites.

After the live tests I simulated the antenna using EZNEC 2. 
My findings are that the folded dipoles have great influence
on one another, when the antenna is not in perfect resonance.
The change in impedance is big enough to give a 3 dB difference
between the vertical and the horizontal field.

I know there are a lot of you using cross yagis with folded dipoles.
Have any of you seen anything like this ??

Thanks in advance.

73 OZ1MY/Ib
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