Digital tuners can develop - Digital Glitches - that are not cleared out with simple channel scans.
Do Double Rescan ,
http://www.wchstv.com/DoubleReScanAlert.pdf.
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Have only the UHF/VHF antenna connected and aim at about 190 degree magnetic compass direction.
Here is how to aim antennas ,
http://www.kyes.com/antenna/pointing/pointing.html.
Use a Old School magnetic compass to aim antenna/s.
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If using both antennas.
Use a Winegard CC7870 transformer type isolation combiner to connect the 2 antennas.
The isloation type combiner reduces antenna cross talk and reduces signal bleed off of the 2 antennas connected to one coax.
And reduces the out of phase signals of the 2 antenna on 1 coax.
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If using both antennas , aim the UHF/VHF antenna at about 211 degree magnetic compass direction and UHF antenna at about 138 degree magnetic compass direction.