-->YES you ave a Excelent reception location.<--
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So what is the make and model number of the antenna.
It looks like a Channel Master CM4228HD UHF/VHF antenna that is desinged to receive UHF channels 14 thru 51 and VHF high band channels 7 thru 13.
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YES you have a Excelent reception location.
The transmission/reception in the Green and Yellow reception zones are Strong Signal Strength and are easy to receive.
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The reception of the VHF high band channels 7 thru 13 will be received even with a antenna that is designed for UHF reception , Reason: the Tv transmissions are Very Strong at your location.
Examples ,
WJLA VHF high band channel 7.
WUSA VHFhigh band channel 9.
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Aim the antenna at about 65 degree magnetic compass direction.
Here is how to aim antennas ,
http://www.kyes.com/antenna/pointing/pointing.html.
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Water damage of outside connections and coax is the most likely cause of reception that gets less and less as time goes by.
As a ->Test<- to prove reception.
Disconnect and remove ALL parts of amplifier , disconnect and remove the amplifier unit , disconnect and remove the power injector , disconnect and remove the power supply.
Connect a ->NEW<- continues length of coax that has the compression type connectors on the ends of the coax , not the old crimp type connectors.
Run the NEW continues length of coax through a open door or window direct to 1 Tv.
No couplers , No splitters , No ground couples , No nothing.
It is the , Antenna , the NEW coax , the Tv.
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Digital tuners can develop -Digital Glitches- that are not cleared out with simple channel scans.
Do Double Rescan ,
http://www.dtv.gov/rescan.html.
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If reception still has problems , then the connection , transformer/balun , of the antenna can be bad from water damage.
->ALL<-> outside connections are suspect of being bad.
And All other connections and coax is/are suspect of being bad through out the whole system , both inside and outside of the building.
Water will get into coax and damage the coax.