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

[Herb Schoenbohm]

I learned the hard way with a 5/8 wave insulated self standing tower on 
to band is basically useless for DX work compared to a standard  1/4 or 
3/8 wave vertical radiator.  As Tom so knowledgeably pointed sending 
radiation close to the ground is not helpful except perhaps for a tall 
tower AM station.  If you have this kind of height available for 
broadcast then a folded Franklin may make more sense.   But one of the 
basic rules of non-Maxwell physics, that so far no one has been able to 
disprove, and remains an undeniable truth for topbanders:  That which 
work best on 160, works!   Now try that one on for size.

Herb Schoenbohm, KV4FZ







On 10/1/2013 8:26 AM, Tom W8JI wrote:
> 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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