Do Not go to radio shack - for any reason.
Do not accept any information that the people at radio shack tell you , 99.9% of the information will not be correct.
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---->Please answer this question. What directions do the , windows and balcony face??<----
Your sister has ->Many<- receivable Digital Broadcast Tv stations/channels at her location.
For a indoor type antenna , install a Terk HDTVi (not HDTVa) antenna in/at a ~ South ~ facing window or a balcony door window.
If a Long coax run through the Apt. is required to get the HDTVi Tv Reception from the HDTVi antenna to the Tv , then so be it.
Window glass , balcony-patio door glass , is less obstruction to broadcast Tv reception.
The building construction that is wood with wood or vinyl siding is more obstruction to broadcast Tv reception.
The following is a Non Complete list of building construction that is More obstruction to Broadcast Tv reception.
Concrete walls and building , concrete blocks , bricks , rocks , metal siding , metal walls , metal roof , metal backed insulation ,
apartments between your sisters apartment and the transmitters , other buildings between your sister apt. and the trasmitters.
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Aim the HDTVi antenna at about 180 degree magnetic compass direction , South.
Here is how to aim indoor and outdoor antennas ,
http://www.kyes.com/antenna/pointing/pointing.html.
Use a real and actual magnetic compass to aim the antenna.
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The Tv Must Channel Scan for the , OTA=Over The Air , Digital Broadcast Tv stations/channels , often named the Air Channels' ~ 'Antenna Channels' in the Digital Tv Setup Menu because the Tv transmissions travel through the Air from the transmitting antenna to the receiving antenna.
Some digital tv's will Automatic channel scan for cable tv channels.
DO NOT channel scan for cable tv channels.
Go into the Tv Setup Menu and select 'Air Channels' ~ 'Antenna Channels'.
Scan for channels.
If some weaker signal strength Tv stations/channels in the Yellow/Red reception zone of the Tvfool Current Plus Pending Applications Included Digital Channel List are not received well then try reception by installing a Winegard , LNA-100 "boost" amplifier.
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As always , trees and tree leaves , plants and plant leaves , have a Negative effect on broadcast Tv reception and so do buildings and other obstructions including your sister own building.
The Best Practice is to install a antenna at a location that has the least amount to no amount of obstructions of any type or kind in the directions of reception.
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Here are some places to buy antennas and etc. .
http://www.solidsignal.com.
http://www.amazon.com.
http://www.winegarddirect.com.