A test of reception using known to be good reception hardware.
Can I make it more clear.
Radio Shack matching transformer ,
http://www.radioshack.com.
#15-1140
#15-1230
Use a New long length of coax.
No splitters , no couplers , no amplifiers , no nothing.
Antenna -> matching transformer -> coax -> Tv , scan for digital broadcast tv channels.
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Using a channel as a reference point.
WVTM-DT 13 NBC.
Is in the Yellow zone , 17.3 NM(dB) , reception at 30 feet antenna height.
The NM(dB) number drops to 4.5 NM(dB) at 15 feet antenna height , weak but still receivable.
Do the reception test.
Always rescan for Digital Broadcast Tv Channels when making changes.
Would also help to get the antenna higher.