Guest post: Interference from a LDG Z-817 autotuner

This actually is a guest post from PE1BVQ Hans. Hans did suffer from heavy noise (S9) on his FT-817 affecting his receive especially from digital weak signals like WSPR and JT modes.

By coincidence I discovered that the noise on my FT-817 with the laptop connected only appeared when the CAT cable is connected through the LDG Z-817.

When the CT-62 CAT interface is connected
directly to the radio the noise disappeared. When searching for the problem I noticed the noise came up even when I touched the Z-817 connector with the CAT cable connector, it was not even plugged in!

The noise disappeared when connecting the PL259 chassis to the earth of the CAT connector. This problem never occured to me as I use the Yaesu FT-817 + LDG Z-817 as a combo as the Z-817 is sticked to the radio. Opening the ATU reveals 2 circuits, one that tunes the antenna and one that controls the memory.

Both circuit negative sides are connected with each other through coil L14. I didn't bother measuring this coil and just made a connection between the connector earths, that solved the problem.

I hope Hans can now finally enjoy digimodes again and actually decode weak signals.
If you as reader has something interesting about the hobby to share and don't want to post it yourself please contact me, I'll be happy to publish it for you here on this blog. The only thing I need are photos and a small story. Dutch will be translated by me. And if desired I will place dutch text as well.