So I've tuned all I can. I am solidly locking 4005 (10.8 dB), 4020 (10.0 dB), 4030 (9.7 dB), 4048 (9.5 dB), 4080 (9.5 dB), 4120 (10.8 dB), 4140 (6.4 dB). But 4180 is just flickering my SNR reading: not anywhere near locked and certainly not viewable. I'll see how it looks later tonight.