Not a surprise.
Strong signal and multipath.
The signal is Very Strong at 74.7 NM(dB).
The attic environment is close in and creates A Lot of multipath - reflected signal bouncing all around in the attic.
Digital Tv Tuners have a circuits that reduce the signal strength in the tuner and can process and eliminate multipath up to a certain point,
And then the Digital tuner is overloaded.
By turning the antenna , you changed some of the multipath reflections to a amount the Digital tuner can deal with.
The 'popular knowledge' is that the stronger the signal the better , ' yea - slam the juice to it!! , more power please!! , crank up the amp's!! , super charge it!! , and so forth!!.
To much signal strength on a Tv channel and the Digital tv tuner will shut down and , No Tv channel for you.
Multipath is not always a negative , sometimes the main signal is not avavliable or good enough to receive.
But the reflected signal is.
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I am curious , is WSKY-Tv channel 9 ,
http://en.wikipedia.org/wiki/WSKY-TV , being received??