I also have noticed similar events with AO-7.  I try to work into Northern Europe when the opportunity is there.  As you mentioned, polarization, obstructions, local noise.  I might add just being a bit temperamental at being up there for 35 years!  I find it remarkable that we are privileged to have access to such a marvelous bucket of bolts.

73 Bob W7LRD

Seattle ----- Original Message ----- From: "Bill Dzurilla" billdz.geo@yahoo.com To: amsat-bb@amsat.org Sent: Tuesday, April 6, 2010 8:07:38 PM GMT -08:00 US/Canada Pacific Subject: [amsat-bb] Re: AO-7 Mode C? (Or other reason for varying signal strength?)

So, folks, does anyone have any thoughts or comments about this issue? 73, Bill NZ5N

--- On Sun, 4/4/10, Bill Dzurilla billdz.geo@yahoo.com wrote:

From: Bill Dzurilla billdz.geo@yahoo.com Subject: AO-7 Mode C?  (Or other reason for varying signal strength?) To: amsat-bb@amsat.org Date: Sunday, April 4, 2010, 10:52 PM

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

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