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Old 31-Mar-2011, 4:24 AM   #1
Junior Member
Join Date: Mar 2011
Location: anaheim, ca
Posts: 13
Impedance matching, directionality, and gain

Originally Posted by No static at all View Post
I agree as well. Just a few inches can make a world of difference, even with a strong signal. UHF can be very fickle.
Just registered. I was using a CM4228 8-bay antenna to get the UHF channels because I believed it would help my reception plagued by multipath. Some channels were strong and some were weak. I would move the antenna a few inches and the weak ones became strong but the strong ones became weak. I could never find a spot where all stations were strong. I read on HDTVPrimer that a large antenna (which has a narrower beamwidth) could actually be more lossy than a smaller antenna. Thus I tried the CM-4221 4-bay antenna and to my surprise all the UHF channels were strong (high S/N), some even stronger than before. Didn't have to move the antenna at all.

My theory of why I got better reception is that the radiation pattern across the smaller antenna was more uniform than across the larger antenna. According to the reciprocity theorem, the multipath signals received creates a very complex signal that is not matched to the transmission line thereby causing reflection which is loss. The losses must have been greater than the 3 dB increase in gain. The received signal from the smaller antenna better matched the transmission line resulting in less loss.

Sorry for being long winded. Your comments or thoughts are welcomed.
retired17 is offline   Reply With Quote