Topband: 5/8 wavelength vertical is mo betta than shorterversions??

[Tom W8JI]

I certainly agree with Richard Fry from a pattern perspective, although my 
experience with 5/8th wave antennas and other low angle tall verticals over 
the past 40 years (and I have had several antennas) is that really low 
angles on 160 for extended groundwave contacts or DX are utterly useless.

If you want a dog of a performer that is good for stuff within 40 miles, use 
a really low angle radiator on 160, especially one that puts a null at 20-40 
degrees. At about 200-220 feet height with flat ground the overall 
performance of a vertical starts to take a dive.

Consequentially, at least on 160 for practical uses, NEC far field is fine. 
Reaching the ionosphere at a low angle that simply uses up the energy in 
losses is not a good design goal, especially when the gain is so small and 
significant energy is removed from more useful angles.

Tom

----- Original Message ----- 
From: "Richard Fry" <rfry at adams.net>
To: <topband at contesting.com>
Sent: Tuesday, October 01, 2013 6:38 AM
Subject: Re: Topband: 5/8 wavelength vertical is mo betta than 
shorterversions??


>>>The radiation toward an elevation angle of 5 degrees shown in the surface 
>>>wave plot continues in essentially a straight line, to reach the 
>>>ionosphere."
>
>>I'm still puzzled by these statements.
>
> Its clear that a NEC far-field analysis over a real earth path omits a 
> significant amount of low angle radiation produced by vertical monopoles. 
> Such an analysis always shows zero radiation in the horizontal plane, and 
> not much more than zero at very low elevation angles.
>
> But if that pattern was correct, then MW broadcast stations would have no 
> daytime or nighttime groundwave coverage -- which obviously they do.
>
> However the NEC near-field analysis used to calculate the surface wave 
> does show that low angle radiation.
>
> BOTH the NEC far-field and near-field analyses are required to describe 
> and understand the total radiation envelope of a monopole over real earth.
>
> For background, I contacted Gerry Burke in January, 2012 when I was
> researching the basis for the comments I have been posting here.  Probably
> most will recognize Gerry Burke as the co-author of NEC software, working 
> at
> Lawrence Livermore National Laboratory.
>
> I sent him the NEC surface wave plots linked below, and asked him,
> "...would you expect the fields at elevation angles of 1 to 10 degrees in 
> these
> plots to continue on to the ionosphere, and under the right conditions
> be reflected back to the earth as skywaves?
>
> His reply was (quoted with his permission): "The low angle 1/R fields 
> should
> reach the ionosphere, although perhaps not accurately predicted by NEC,
> since it does not include the effects of earth curvature and the
> ionosphere."
>
> G. Burke's reply should be conclusive on this subject.
>
> BTW, the 2.46 V/m groundwave field shown at 1 km from the WLS tower for 8 
> mS/m earth in the NEC plots linked below is almost exactly the value 
> measured at 1 km by the newly-retired chief engineer of WLS, who is an 
> acquaintance of mine.
>
> http://s10.postimg.org/xq4ngg4hl/WLS_Surface_Wave.jpg
>
> RF
> _________________
> Topband Reflector
>
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