iphone 4 wifi signal keeps dropping

Iphone 4 WIFI signal keeps dropping.
location: apple.com - date: June 4, 2012
Hello could someone help me? I have had my iphone 4 for about 4 5 months as this was a replacement. But now i keep having this issue. I have had it for about a month. I connect to my internet and it works perfectly. Surfing the web facebook all works. But soon as i go on to youtube and click on a video every 4 - 5 minutes the wifi signal drops and to get it back i have to ecit to the home screen and wait for a couple of seconds. Then i go back onto the video and it happens again. This happens on alot of WIFI connections not just my one what could be the issue?
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