Dave,
yes it puzzles me too...
Fact is that it does make a tremendous difference with my BITX40 (the
birdie went down from S9++++ to virtually zero). Some other builders don't
notice so much difference.
Some time ago we had a discussion on this forum about the 7199 birdie. See
Hans Summer's posting #22023 with his ideas of what's causing it.
73, Allard PE1NWL