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In order to generate circular polarization in a crossed-yagi, a 90° phase delay is required between the horizontal and the vertical antenna. In practice, this is achieved either by making a mechanical shift of lambda/4 or by using phasing stubs. However, some cots antenna have a mechanical plane offset different than the lambda/4. Indeed in my case, I have a 70cm 2x19 elements antenna from Tonna that I want to set up for satellite operations. To achieve right-hand circular polarization, a phasing harness was purchased http://www.wimo.de/download/1808xx.pdf.

In the antenna datasheet, a mechanical offset of 200mm is specified. When consulting other forums and by using online phasing calculators, an extra length of -18.83 mm is needed (see screenshot). On the other hand, the phasing calculations provided in the harness datasheet are totally different.

Can someone please give me a clue here? I would reaaaaally appreciate it. I'm really lost.

enter image description here

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The problem with the result of the online calculator you pictured is that your DE spacing is already greater than $\lambda$/4 (~172 mm). As a result, you must remove the indicated length from the coax feeding the leading DE in order to achieve an overall 90 degree phase shift . That is to say that your mechanical spacing is 105 degrees so you need to remove 15 degrees from the harness in order to achieve a total phase shift of 90 degrees.

The WiMo formula, on the other hand, is simply wrong - unglaublich!

The correct formula for DE spacing <$\lambda$/2:

$$L_{physical}=(\lambda/4-\Delta_{DE})*VF \tag 1$$

where $\Delta_{DE}$ is the distance between driven elements and $VF$ is the velocity factor of the coax. A negative result indicates the coax must be shortened by that amount as noted above.

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    $\begingroup$ Thank for the quick reply. I agree that the wimo formula is no good, and I totally understand that 18.8 mm of cable shall be removed, but from which one: the horizontal or the vertical feedline? In other words, what is going to be the length of the 50 ohms Lv and Lh cables feeding the horizontal and the vertical DE? I really don t see how to remove the 15 degrees from the harness. Best $\endgroup$ – Ibtissam Latachi Dec 21 '18 at 13:24

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