I apologize if this isn't the correct Stack on which to ask this question, but it seemed like the best fit. I've tried to Google an answer, but I haven't been able to find anything that applies directly to Es/No, or which is written in a way I can understand (ie, the mathematical formulas on Wikipedia are beyond me at the moment).

I have worked with legacy satellite communications equipment for years, and I am typically used to seeing receive signal performance measured as a positive Eb/No or Es/No; any carrier visible on a spectrum analyzer would have--in my experience--a positive Es/No value.

However, I was recently shown an SCPC system where the carrier's Es/No was reported as a negative value, but I can't get an explanation as to why. Is a negative Es/No value even possible? Specifically, is such a value possible for a carrier which appears to be above the noise floor (as seen on a spectrum analyzer)?

If it's possible, then what would such negative values signify?

I appreciate any insight anyone can offer, even if it's just to point me to another Stack.