Rob, this has been discussed on the group here previously, this is a common outcome for the high band QDX builds, my rev 5 was this way, too. 20 and 17m share the same BPF, and there's interactions between the other BPF slots, extra capacitance from the PCB, and more. Hans has stated this is a compromise that had to be made to fit all bands in. This is part of why the QMX midband uses 2 separate toroids for the BPF, and the QMX+ uses only 2 bands per BPF toroid....it helps keep the BPF slots from interacting with each other. I think Hans may have softened the L-C sharpness of the BPF values in general, too...but not positive.?
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I use a low band QDX and my high band QDX on the same antenna, and I just increased the audio level on the high band...it's not really noticeably worse in reception on 20m.?
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I struggled to make some of the bands sweep well with a mid-band QDX I built (40-15m), and ended up just bypassing the BPF entirely, and run a K9DP BCI filter in front of the QDX for <3.5 mhz. So far has worked fine in the US.
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-Nate
N8BTR
