Well, the TNC-M bulkhead pigtails that I’d received from a buddy of mine were great, but more sensitive to stripping stress than I’d considered. I suspected that I’d possibly damaged one last weekend while preparing the end – pays to have a very sharp wire stripper that grabs the insulation fully and doesn’t touch the copper.

Anyway, appears that I stressed one of the two coaxes enough that it’s officially intermittent with temperature, and has now at least a 20 dB signal loss over it’s performance last Sunday. Se la vie – I will repair it tomorrow.

Update: 10DEC16

Replaced damaged TNC pigtail with a new one. Discovered also that a TNC-f to TNC-f adapter was marginal, and replaced that with another cable I found in the garage. Everything is working well now!