John WBOCMC has a tech article in the August 2023 QST magazine on p.50. He made an audio signal generator, engineered it, and even made the circuit board himself. Wait, it gets better. He’s making his own ADF (Automatic Direction Finder) system, and to test it he needed 2 audio signals in quadrature (same freq – one offset 90 deg phase). So he made it.
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Expand the pic above. You may be able to read it right here. The circuit board on the right, next page, has 5 ICs and some other parts on it.