Test reception without the , preamplifier , power injector , power supply.
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Test reception with the ANT751 antenna aimed at about 170 degree magnetic compass direction.
Here is how to aim antennas ,
www.kyes.com/antenna/pointing/pointing.html
Use a Real and Actual magnetic compass to aim antenna.
Digital tuners can develop - Digital Glitches - that are not cleared out with simple channel scans.
To Clear Tuner , Do Double Rescan ,
www.wchstv.com/DoubleReScanAlert.pdf
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www.coaxseal.com , works better then silicone sealer.