[TowerTalk] re Radials

[Joe Giacobello]

It is my understanding that a hilltop and the proper terrain can make 
all the difference with a horizontal antenna.

Another correspondent to this list compared a horizontal antenna on a 
500' tower on flat ground vs the same antenna on a 100' tower on a 400' 
hilltop with the ground sloping off at 45 degrees using HFTA "...and the 
two vertical patterns [were] essentially identical."  Since the 
effective height of an antenna is determined relative to the terrain 
2-1/2-3 wavelengths from the antenna, a 100' high 160M dipole on such a 
hilltop would be effectively one wavelength high and would have a TOA of 
about 15 degrees.

I am not disagreeing with anything that has been said in previous posts, 
but just underscoring that terrain has to be taken into account when 
making these kinds of comparisons.

73, Joe
K2XX

Bill Coleman wrote:

>On Jun 16, 2006, at 10:11 AM, Bill Turner wrote:
>
>  
>
>>Yes, I know verticals have a lower radiation angle, but on 160/80/40
>>most signals arrive at high angles anyway. On the higher frequencies
>>a vertical would be more practical, but there most folks use beams.
>>    
>>
>
>Horizontal antennas, like dipoles, make great antennas, but they are  
>affected by proximity to the ground. They have to be at least 1/4  
>wave above ground before the radiation pattern is anything but  
>straight up. Dipoles don't start to have a distinctive bi-directional  
>pattern until they are about 1/2 wave or higher.
>
>For 160, this means a couple of 40m or 80m high supports. That's 133  
>to 266 feet high! For 80m, that's at 66 to 133 feet high. Few hams  
>have antenna supports this high.
>
>For 40m and higher, many hams have the resources to mount horizontal  
>antennas sufficiently high for them to be effective antennas, even  
>for DX. But for 160m and 80m, finding sufficiently high supports is  
>impractical.
>
>There's also evidence that suggests that verticals may be more  
>effective low-band antennas. W8JI relates that his 300 foot high  
>dipole for 160m is only more effective than his verticals under very  
>special propagation conditions. For more than 90% of operating time,  
>the verticals work better.
>
>Bottom line, for the typical ham, compromise verticals are more  
>effective DX antennas than compromise dipoles on 160 and 80m.
>
>Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net
>Quote: "Not within a thousand years will man ever fly!"
>             -- Wilbur Wright, 1901
>
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