The Federal Antenna Law provides for you the right to install a antenna out on the balcony.
http://www.fcc.gov/mb/facts/otard.html.
As you now know , concrete blocks Tv reception and what Tv signals do make it to the inside of the building through doors windows , are multi-path reflected - bouncing all around over and over again , this Is Not good for reception.
And at your location the Tv reception is Very Strong Signal Strength , so Very Strong Signal Strength Tv signals bouncing all around is now the 2 times Not Good for Tv reception.
The 2 times not good signals bouncing all around are made even worse and are now Triple Not Good when amplified.
Do Not use a amplified antenna or amplifier of any type or kind.
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Install a Antennas Direct , Clear Stream 2 Complete VHF/UHF antenna out on the balcony , aimed at about 164 degree magnetic compass direction.
http://www.antennasdirect.com/store/...VHF-Combo.html.
Get the antenna as much as you can , out in the clear on the balcony for reception of the Tv transmitters to the , south west , south , south east.
Most of the Tv transmitters to the southward type direction are to the , south , south east.
As always , the starting antenna aim direction is the -->starting antenna aim direction.
The antenna aim direction can be adjusted for best reception.
Most Digital Tv's have a Signal strength meter and some digital Tv's also have a signal quality meter.
Here is how to aim antennas ,
http://www.kyes.com/antenna/pointing/pointing.html.
Here are some places to buy antennas and etc. .
http://www.solidsignal.com ,
http://www.amazon.com.
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Also Digital Broadcast Tv Tuners can develop - Digital Glitches - that are not cleared out with simple channel scans.
Do Double Rescan.
http://www.dtv.gov/rescan.html.