[TowerTalk] optimum vertical length

[Joe Subich, W4TV]

> Curiously enough, though,  on both those bands, there are times when  
> signals arrive at high angles.  At a sunspot peak, for example, at mid 
> day,  if you don't have a 10m  yagi @ 25',  you won't break
> contest pileups.

Even a low Yagi (25' on 10 meters) has a take off angle around 15 degrees. 

The 43' vertical is much too tall to be usable on 15 and particularly 
10 meters.  On 10 meters the dominant lobe is at 57 degrees (3.7 dBi). 
The pattern is less than 0 dBi below 45 degrees and almost - 10 dBi 
below 15 degrees.  On 15 meters, the only lobe peaks at around 3.5 dBi 
with a take off angle around 40 degrees and drops below 0 dBi around 
25 degrees. 

On both 10 and 15 meters a majority of the radiation will occur above 
the "critical angle" of the ionosphere and will pass into space without 
being reflected back to earth. 

73, 

   ... Joe, W4TV 
   




> -----Original Message-----
> From: towertalk-bounces at contesting.com 
> [mailto:towertalk-bounces at contesting.com] On Behalf Of jim Jarvis
> Sent: Monday, June 01, 2009 7:53 AM
> To: towertalk at contesting.com
> Subject: Re: [TowerTalk] optimum vertical length
> 
> 
> 
> Jim,
> 
> 43' was chosen as a length because it represents 5/8 wave on 20m,  
> which is the point at which
> a higher angle lobe starts emerging, but groundwave is maximized.
> 
> Clearly, the antenna is the biggest it can be, to produce best 80m  
> performance, while retaining
> best 20m performance.   160 is compromised.   15 and 10 are  
> compromised by multiple lobes.
> 
> Curiously enough, though,  on both those bands, there are times when  
> signals arrive at high angles.
> At a sunspot peak, for example, at mid day,  if you don't have a 10m  
> yagi @ 25',  you won't break
> contest pileups.
> 
> So, the only answer is,  "it depends".
> 
> Regardless of the electrical length of the antenna, though,  getting  
> it up high and in the clear
> is the important factor.   A 40m vertical dipole plays 
> amazingly well  
> on multiple bands, with
> a tuner, if you can get the high current portion of the antenna up  
> 50' or so, in a tree.
> 
> N2EA
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> 
> 
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