How to use 70 cm WiMo phasing harness for a COTS crossed yagi antenna?

Question

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.

Answer 1

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.