A call to the engineering departments of these stations confirms that the Tv transmissions are Analog transmissions and are transmitting.
Aim the XG91 at 270 degree magnetic compass direction.
KNTL-LP UHF channel 47 , Univision.
K22DR UHF channel 22 , CBS.
K18CB UHF channel 18 , MyNetwork
And , Fox , ABC , are also received at 270/269 degree magnetic compass direction.
And PBS using the HD5030 antenna.
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So that leaves Digital channel NBC UHF channel 50 , at 122 degree magnetic compass direction.
I recommend install a Separate UHF antenna , a Channel Master 4228HD antenna aimed at about 122 degree magnetic compass direction.
Install a Remote control A/B antenna switch ,
http://www.mcmelectronics.com , #32-4425 , or ,
http://www.radioshack.com , #15-1968 .
To change antennas , west group of Tv stations and south east group Tv stations.