Topband: Modeling close to earth ( was Odd-ball question)

[Artek Manuals]

Jerry et all

My personal antenna FOR 160 was/is as follows

160M T:
   60' Tall with with a 78' flattop. The "bottom"  is at 7' ( so the 
actual vertical element is 53') with three 90' radials at 7' spaced 
pretty nearly in 60 degree increments ( 60, 120, 240). There is a tapped 
inductor in series with the ground side (NOT the vertical side) of the 
feed point used to resonate the whole thing . For the general approach 
to loading and using non-resonant radials I was strongly influenced by 
K5IU's work in Spring 1997 Communications Quarterly  (google should  
find you reprints of that) . The vertical is #14 bare stranded copper 
and the radials are #10 Bare solid copper ( no magic on sizes etc just 
what I happened to have on hand.  Ezenec  says this should be around 13 
ohms at 1840 resonance ( with a 23uh series inductor) . In practice it 
is closer to 25ohms at resonance  with a about 17uh of inductance.

It is then matched with a 2:1 UNUN to 50 ohms. This antenna REALLY NEEDS 
and uses a common mode choke at the feed point . This turned out to 10 
to be ten FT-240-43 torroid's with 4 turns of coax through the batch, 
lesser amounts of ferrite became quite hot.

After the smoke clears it all appears to work very well I have worked 24 
countries on 5 continents ( still need Antarctica and Asia...tough on 
any band from FL) in just 4 SUMMER months and I am sure that total will 
climb quickly once the winter season starts. For the FT8 doom and 
gloomers half of these were on CW....8^)

Happy to share details of the 80 and 40 M antennas off list, not 
relevant  to the topband list !

Dave
NR1Dx
manuals at artekmanuals.com




On 8/25/2019 1:33 AM, K4SAV wrote:
> Dave
>
> Just a clarification.  I didn't want your actual data.  All I wanted 
> was the length of the wires and the frequency.
>
> Jerry
>
> On 8/24/2019 9:30 PM, K4SAV wrote:
>> Hey Dave
>>
>> I'm interested in your data.  How long were the radials and what 
>> frequency were you using for the measurements.
>>
>> I suspect that NEC2 may be close enough to be generally useful 
>> (accuracy is questionable) for a BOG up to 250 ft on 160.  My 
>> measurements (several of them) say that NEC isn't close for a 350 ft 
>> BOG.  Usually my BOGs are 1 to 2 inches above the dirt because they 
>> sit on dead grass.
>>
>> I seriously doubt that NEC4 will be accurate for a 350 ft BOG 
>> either.  I have seen a 450 ft BOG pattern generated by NEC4 and I can 
>> duplicate it with NEC2, (with only minor insignificant squiggle 
>> differences) and I know that NEC2 is wrong.
>>
>> I suspect that as frequency decreases or the wire becomes shorter, 
>> NEC answers will improve.
>>
>> A data point from someone else would be nice to know.
>>
>> Jerry, K4SAV
>>
>>
>> On 8/24/2019 7:53 PM, Artek Manuals wrote:
>>> Chuck et all
>>>
>>> It is well documented that the the NEC-2 based programs leave 
>>> something to be desired� with wires on or very near the ground, This 
>>> includes most of the EZENEC� family and MMANA-G� Purportedly NEC-4 ( 
>>> there is a Ezenec version which runs with NEC 4 engine ... not a 
>>> cheap date) does deal with the near earth problem .
>>>
>>> How close is "Close" is a matter of conjecture. A friend of mine and 
>>> I have been working on building and modeling vertical antennas ( 
>>> Verticals, Inv-L and T's) for 160/80/40 with ELEVATED NON-RESONANT 
>>> radials at 3' and 6' (google "K5IU Elevated Radials") . The good 
>>> news is at 3' and above both NEC 2 and NEC 4 models agree within 5% 
>>> or better.� We have not done any comparisons below 3'
>>>
>>> Dave
>>> NR1DX
>>>
>>>
>>> On 8/24/2019 1:41 PM, Chuck Dietz wrote:
>>>> I seem to remember someone saying the modelling programs are 
>>>> unreliable
>>>> when a wire is close to the ground. Also, there is really no way to 
>>>> model
>>>> the properties of "ground." It can vary in just a few feet and the 
>>>> moisture
>>>> content varies from day to day. I think this is a "try it" kind of 
>>>> antenna.
>>>> Read other's reported results.
>>>>
>>>> Chuck W5PR
>>>>
>>>>
>>>
>>
>
>

-- 
Dave
Manuals at ArtekManuals.com
www.ArtekManuals.com


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