[amsat-bb] AO-7 Mode C? (Or other reason for varying signal strength?)

[Bill Dzurilla]

Hi folks,

Since starting my effort to work Europe on AO-7, I've found that the very low elevation sigs vary significantly on different 
passes.  Some mornings I can easily hear my downlink and start working 
Europe at 0.7 degrees elevation, while other days I can't hear myself 
until 5 degrees elevation, after the window to Europe has closed.  Not 
sure if this is due to band conditions, satellite polarization, 
obstructions at certain positions, operator error, local noise, or what.

Today I spoke with another experienced AO-7 op and he had an interesting theory: on the bad days (when I don't hear my downlink until 5 degress), the sat is in Mode C (lower power).  This seems to make sense, because there does not seem to be any middle ground -- I start hearing my downlink at either 0.7 degrees or 5 degrees, never at 2-4 degrees.

Anyone have any thoughts on this?  Are we able to predict when the sat will be in one mode or another?  Or any other explanation for the signal strength variations?

73, Bill NZ5N