First , falling of the roof of the house is , very close to zero fun , so do not fall off the roof.
The following test is best done with , no , wind , rain , snow , ice.
A small test antenna , ANT751 , can be mounted to Tv antenna mast sections , and hold up in the air up high , as a test of reception.
A chimney antenna mount , tripod antenna mount , eave antenna mount , can be used as a 'test stand' , and add mast sections and keep pushing the antenna higher.
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Also if you can get on the roof of the obstructing building , and put your head down low to the top edge of roof of the obstructing building and look out to the roof of the 3 story house , that would give you an idea of how high the the test antenna will have to go.
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In your favor the Digital Tv stations are Strong Signal Strength at your location.
And there is the scatter effect.
As the signals come across the obstructing buildings roof , some of the signal is bent downward.
The scatter effect is not evenly distributed , so will most likely require , moving the antenna up and down to find hot spots.
Also if toward the top end of the mast pipe section below where the ANT751 is clamped to , is bent , so the ANT751 front of the antenna is 'looking' up at a angle of about , 5 to 15 degree , that will put the length of the ANT751 in better alignment with scattered signals that are bent downward at a angle.
And can also help to try other locations , backwards , forward , left and right.
The best reception will be with the antenna location , north , away from the building that is blocking reception
In the old days it was called walking the roof , holding the antenna , looking for hot signal spots.
You may find that the signal strengths are reliable with out going too high.
It is a Experimental situation.
The Canada Digital Tv stations to the , south east are , CHCH - Independent , CHCJ - CTV TWO , CITS - Religion.
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An other way to do the test is , if you can make a deal with some one that has truck that has the hydrulic arm and bucket , like tree trimmers use , ect. , use.
Then is easy to test and install the antenna above the roof of the house.
If the antenna can be installed at a height that clears the buildings roof to the south then the antenna will not need to be tipped up at a angle.
As part of the test to prove reception , connect a NEW loooong coax to the antenna and run the NEW loooong coax through a open door or window , direct to 1 Tv.
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Another way to watch the channels is ,
http://www.slingbox.com .
The Sling Box and a Digital Broadcast Tv Tuner are placed at a location where the Tv Transmitter is easy to receive.
The Sling Box , Tuner , combination , will send the Tv channel over the internet to your Tv.
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An other way to do it is , many Tv stations can be received directly from the Tv stations web site.
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An other way to do it is , move to a location that provides easy reception of all the Tv transmitters.