Mike's updated phase shifter



    Dana designed a  phase shifter that input a single hf freq, and output 6 copies of this, each with a programmable amplitude and phase shift. This allowed us to generate the circular polarizations needed for the ionospheric studies.

    The technique split an HF signal into 6 copies (one for each dipole). Each of these signals was input to the lo inputs of  2 mixers (with a 90 deg phase shift). The IF input of the mixers was driven by dacs outputing DC levels. The output of the two mixers was then combined and output to a dipole. By changing the amplitude of the dac outputs, the amplitude and phase of the signal to a dipole element could be set.

This worked fine until we tried to do AM modulation, and dual frequency experiments. Since the lo input of  a mixer is non-linear, what we got out was not what we put in. (more info)

    Mike came up with a technique to get around this problem.

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