Thanks for all your replies.
I would like to explain more, Here are my list of
http://www.tvfool.com/?option=com_wr...60b5c446db19dc
remember, only Digital TV channel available now.
I did try with 15 inch vertical wire ( May be 3db gain) on roof, I get all local channel but missing all 3 of USA channel signal strength between 74dbm to 84dbm
I made a cloth hanger DB4 antenna ( May be 6-8DB gain but 300ohm matching transformer lose 4db+) and mounted it on roof and I get the same result as 15' wires, Also it is a troublesome design, using for 2 months, I am having poor connection problem (rusting, Very wet here) so I took it down.
I tested with an old indoor RCA pre-Amp Loop VHF/UHF antenna ( Indoor only not on roof), about 20db gain, I got all local plus all USA channels but not very stable.
My understand is that, I need to increase signal strength above -70dbm, to pick up those weaker USA TV signal( -74 to -84dbm, It means that I need 14db in Antenna, it is hard for Antenna only but very easy with good Antenna with pre-AMP for this type of Gain.
I would rather to have a wider horizontal beam wide antenna with more narrower vertical beam wide antenna, Like quad type of antenna design.