I saw some <-30dB decodings again at 28MHz real low signal levels that are not audiable
like -32dB DK4OG -33db & -32dB & -30dB TF3HZ 3x in the 30 range! it happens every 40 spots or so. a -30dB is a very thin trace on the screen. Normaly it will not decode but if the signal quality is good it can decode. Some much stronger signals can give no decodes sometimes.