TX ports question

Hello all ,
I am building a ground station using the LimeSDr and doing comparison on multiple options for the ground station. One of our questions is antennas. We are looking at using two antennas, but we would need them to be out of phase by 90 to achieve circular polarity. I have not been able to find on the data sheet, but I was wondering if anyone knew if the TX ports on the LimeSDR are out of phase or if they are not.



I did some measurements using an oscilloscope at 13.56 MHz - both TX ports are in phase.

Having said that, it’s simple enough to put the necessary phase shift into the two data sets you’re sending out; you can pre-compute the phase shift and cook it into the digital data.

Easier yet is to just use one port with a CP antenna. Helicals are by far my preference; they have high gain and wide bandwidth, and between ~500 and 3000 MHz can easily be built out of common materials (baking sheet ground plate and a PVC support for a Romex helix). A capacitive paddle at the ground end will match to 50 ohms over a 1.8:1 frequency range.

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