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#1
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Circular V.S. Vertical antenna polarization !
I'm interested in real results between this two antennas, urban area, same
power, same high etc. Running circular we have only 50% of power, compared to normal dipole, but there are many positive feedbacks about circular polarization in urban area! Is this really true? |
#2
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Lex-Lutor wrote:
I'm interested in real results between this two antennas, urban area, same power, same high etc. Running circular we have only 50% of power, compared to normal dipole, but there are many positive feedbacks about circular polarization in urban area! For FM, yes, circular polarization is a very good thing. Part of it is because the antenna orientation no longer matters; your listener can have a vertical whip in a car or a horizontal dipole and still get good reception. In addition there are some serious benefits in reduced multipath, many of which really only apply if the listener has a circularly polarized receive antenna, but some of which are of benefit even with a whip. Is this really true? Yes. Pretty much everyone today is running some sort of circular polarization. The real difference is in the antenna patterns and how low the angle of radiation is. You don't want to waste your signal by sending it out into space or into the ground. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#3
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"Lex-Lutor" wrote in message ... | I'm interested in real results between this two antennas, urban area, same | power, same high etc. Running circular we have only 50% of power, compared | to normal dipole, but there are many positive feedbacks about circular | polarization in urban area! | Is this really true? In a manner of speaking, yes, it's true. The reason why you have 1/2 the power that you would with a straight dipole is because half the power transferred goes into the other polarisation (10kW ERP = 5kW Horiz + 5 kW Vert). And the reason why one uses vertical polarisation is for the number of automobile receivers that have vertically-oriented antennas. But, other than that (with one exception which I'll cover presently) there's no good reason why you'd run C-pol. For the rare individual who has a C-pol receiving antenna, (s)he'd be picking up both polarisations, and therefore get 3dB better signal-to-noise....but in an urban area, that effort is for naught, since there's already plenty of RF, and twice more than plenty is still more than plenty. For the rest of those using dipoles in random orientations, they're just as susceptible to multipath, fading, and other propagation effects that would be experienced with a single polarisation. Still, there's some value in this since it wouldn't make any difference which orientation a simple dipole was in, if it had a C-pol signal to work with. -- ----------------------------------------------------------------------------- Men born to freedom are naturally alert to repel invasion of their liberty by evil-minded rulers. The greatest dangers to liberty lurk in insidious encroachment by men of zeal, well-meaning but without understanding." -- Justice Brandeis ----------------------------------------------------------------------------- For direct replies, take out the contents between the hyphens. -Really!- |
#4
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"Lex-Lutor" wrote in message ... I'm interested in real results between this two antennas, urban area, same power, same high etc. Running circular we have only 50% of power, compared to normal dipole, but there are many positive feedbacks about circular polarization in urban area! I did extensive empirical testing in Quito, Ecuador in the mid 60's on HCTM1, using both horizontal and vertical polarization. I ended up with only vertical, which reduced the multipath from the reflection of the hills and mountains considerably. At that time, HCTM1, 95.1, was the only FM on the air in that city of 700,000 lying in a valley in the Andes, so it was a good test of signal. Since we were the only FM for about 1000 miles around, we could do pretty much whatever we wanted. |
#5
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Lex-Lutor wrote: I'm interested in real results between this two antennas, urban area, same power, same high etc. Running circular we have only 50% of power, compared to normal dipole, but there are many positive feedbacks about circular polarization in urban area! Very, very much not an urban setting, but West Virginia Public Radio was exclusively horizontally polarized at most, if not all, their dozen mountain top transmitters. The chief emgineer contended it worked better in the mountainous terrain. Their situation might have assumed a fixed transmitter power out, thus the circular would result in half the ERP (per polarization). I note that they have recently obtained construction permits to convert to circular. Perhaps they are buying new transmitters - which will have much higher efficiency. This way the power bill and wires up the mountain need not change (much) to get the higher transmitter output needed to maintain the same horixontal ERP when going to circular. |
#6
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Robert J Carpenter wrote:
Very, very much not an urban setting, but West Virginia Public Radio was exclusively horizontally polarized at most, if not all, their dozen mountain top transmitters. The chief emgineer contended it worked better in the mountainous terrain. Their situation might have assumed a fixed transmitter power out, thus the circular would result in half the ERP (per polarization). I think this was the case at the time when most listeners were at home with horizontal folded dipoles. I note that they have recently obtained construction permits to convert to circular. Perhaps they are buying new transmitters - which will have much higher efficiency. This way the power bill and wires up the mountain need not change (much) to get the higher transmitter output needed to maintain the same horixontal ERP when going to circular. The big deal is that in the past 15 years or so, radio listenership has moved very much into the car (even for NPR which tends to have more home listeners than most stations) which has made vertical components that much more important. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#7
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"Scott Dorsey" wrote in message ... Robert J Carpenter wrote: Very, very much not an urban setting, but West Virginia Public Radio was exclusively horizontally polarized at most, if not all, their dozen mountain top transmitters. The chief emgineer contended it worked better in the mountainous terrain. Their situation might have assumed a fixed transmitter power out, thus the circular would result in half the ERP (per polarization). I think this was the case at the time when most listeners were at home with horizontal folded dipoles. The chief engineer claimed that it worked better in his car as well. YMMV. |
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