Peter,
I didn't need to remove C91 on my BitX40 board, only L4 and it works perfect with a Si5351 and a Arduino, however i too was getting harmonics from the Si5351, so I added a LPF between it and the BitX board and now it works great with a much lower noise floor.
Joel KB6QVI
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On Dec 17, 2016, at 12:43 PM,
parkerp@... [BITX20] <
BITX20@...> wrote:
?
Adding a DDS isn't all plain sailing. ?
I got a horrible whine that was coupled into the BitX via the power supply rail. ?I needed to add some caps and big RF choke to provide isolation. That removed about 95% of it so it's hardly noticeable unless the antenna is removed. ?Another choke should fix it completely.?
Also I sometimes hear a lot of carriers from SW broadcast signals when tuning 7 MHz that weren't there when using the free running VFO. My theory is that it's a harmonic of the DDS VFO but I haven't tracked it down yet.?
Joel Caulkins/N6ALT