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"Walter Maxwell" wrote in message ... On 10 Sep 2004 16:10:57 GMT, Allodoxaphobia wrote: I am a newbie here and have just dropped in to ask a single technical question. Living as I do in a suburban area, I use an FM antenna to draw the stations located in a certain vector from me. A station of interest is located at 107.1MHz but is interfered with by an off-axis stronger signal at 106.9MHz Hello Bryce, I'm sure you're aware that these two frequencies are adjacent channels. The FCC allocated channels such that adjacent channels stations would not be located in the same geographical area, expressly fo the purpose of preventing such interference. Obviously the two channels involved are not in the same area, and it seems strange to me that you can even hear the station on 107.1 MHz. ..... Walt, W2DU When you are BETWEEN markets, this is common. Or, if you want to listen to a distant station and the wrong one is close. I'm equi-distant from Chicago, Milwaukee and Rockford and have this problem hearing WDCB 90.9, west of CHi-town with WHAD 90.7, S-W of Milwaukee pounding in. They're in different markets. This was discussed not to long ago here. A notch in the antenna pattern is not too difficult. Two vertical dipoles spaced (about) a half wave and fed with the proper feed line so they are 180 degrees out from each other, can make a nice null - actually two. They are perpendicular to the plane of the antennas. I'd have to sit and tinker to remember the feed system, but there has to be 1/2 wave more feed line in one dipole, compared to the other. It is also possible to do the same thing and get a one notch pattern (cardioid). If I recall, the antennas are spaced 1/4 wave apart and the feed is 3/4 wave of feed line between them. Again, the receiver simply connects to one of them and the null is off one end. -- Steve N, K,9;d, c. i My email has no u's. |
#2
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On Fri, 10 Sep 2004 13:38:34 -0500, "Steve Nosko"
wrote: When you are BETWEEN markets, this is common. Or, if you want to listen to a distant station and the wrong one is close. I'm equi-distant from Chicago, Milwaukee and Rockford and have this problem hearing WDCB 90.9, west of CHi-town with WHAD 90.7, S-W of Milwaukee pounding in. They're in different markets. This was discussed not to long ago here. A notch in the antenna pattern is not too difficult. Two vertical dipoles spaced (about) a half wave and fed with the proper feed line so they are 180 degrees out from each other, can make a nice null - actually two. They are perpendicular to the plane of the antennas. I'd have to sit and tinker to remember the feed system, but there has to be 1/2 wave more feed line in one dipole, compared to the other. It is also possible to do the same thing and get a one notch pattern (cardioid). If I recall, the antennas are spaced 1/4 wave apart and the feed is 3/4 wave of feed line between them. Again, the receiver simply connects to one of them and the null is off one end. Yeah, Steve, but isn't FM broadcast wirh horizontal polarfization? With vertical dipoles the only signal you'll receive is from reflect;ions off objects such as buildings. What kind of reflection coefficient would one expect ? Enough for a good signal? Walt |
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"Walter Maxwell" wrote in message ... On Fri, 10 Sep 2004 13:38:34 -0500, "Steve Nosko" wrote: When you are BETWEEN markets, this is common. Or, if you want to listen to a distant station and the wrong one is close. I'm equi-distant from Chicago, Milwaukee and Rockford and have this problem hearing WDCB 90.9, west of CHi-town with WHAD 90.7, S-W of Milwaukee pounding in. They're in different markets. This was discussed not to long ago here. A notch in the antenna pattern is not too difficult. Two vertical dipoles spaced (about) a half wave and fed with the proper feed line so they are 180 degrees out from each other, can make a nice null - actually two. They are perpendicular to the plane of the antennas. I'd have to sit and tinker to remember the feed system, but there has to be 1/2 wave more feed line in one dipole, compared to the other. It is also possible to do the same thing and get a one notch pattern (cardioid). If I recall, the antennas are spaced 1/4 wave apart and the feed is 3/4 wave of feed line between them. Again, the receiver simply connects to one of them and the null is off one end. Yeah, Steve, but isn't FM broadcast wirh horizontal polarfization? With vertical dipoles the only signal you'll receive is from reflect;ions off objects such as buildings. What kind of reflection coefficient would one expect ? Enough for a good signal? Walt To the best of my knowledge- commercial FM broadcast has transmitted on both V and H for many years- how else would a vertical whip on an automobile receive FM? Dale W4OP |
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On Fri, 10 Sep 2004 23:18:13 GMT, "Dale Parfitt" wrote:
"Walter Maxwell" wrote in message .. . On Fri, 10 Sep 2004 13:38:34 -0500, "Steve Nosko" wrote: When you are BETWEEN markets, this is common. Or, if you want to listen to a distant station and the wrong one is close. I'm equi-distant from Chicago, Milwaukee and Rockford and have this problem hearing WDCB 90.9, west of CHi-town with WHAD 90.7, S-W of Milwaukee pounding in. They're in different markets. This was discussed not to long ago here. A notch in the antenna pattern is not too difficult. Two vertical dipoles spaced (about) a half wave and fed with the proper feed line so they are 180 degrees out from each other, can make a nice null - actually two. They are perpendicular to the plane of the antennas. I'd have to sit and tinker to remember the feed system, but there has to be 1/2 wave more feed line in one dipole, compared to the other. It is also possible to do the same thing and get a one notch pattern (cardioid). If I recall, the antennas are spaced 1/4 wave apart and the feed is 3/4 wave of feed line between them. Again, the receiver simply connects to one of them and the null is off one end. Yeah, Steve, but isn't FM broadcast wirh horizontal polarfization? With vertical dipoles the only signal you'll receive is from reflect;ions off objects such as buildings. What kind of reflection coefficient would one expect ? Enough for a good signal? Walt To the best of my knowledge- commercial FM broadcast has transmitted on both V and H for many years- how else would a vertical whip on an automobile receive FM? Dale W4OP You're right, Dale, my age and ignorance are showing. Walt |
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