Well, mystery partly solved.
I was engaged in some due dilegence, doing searches in various bands, mainly in the 150 - 156 MHz area, which is SMCAS' original home, and finally got a hit on 151.3350 (this on my Uniden BCD396T). I've gotten hits here before, when 151.3325 was first established. This I attribute to my radio's selectivity slop with the 2.5 KHz channel spacing.
Then, I went back to 151.3325 MHz, already in my radio, and turned off the PL setting (118.8). Voila! That seems to be the issue. I would say, unless we get word otherwise, that the PL was changed on 151.3325. I only use PLs when I'm trying to keep the channel from opening the squelch due to skip, as there isn't any other receivable traffic around here on that freq. So maybe I'll find out what the current PL is and post it, unless OpusX beats me to it.
Too bad I didn't find this out yesterday evening, as there was a rare ambulance call just a block away from where I live.
