Also:
There are some things that the software can't analyze. It can't handle
an arbitrary terrain. It has only a very limited capability in this
area. It can handle flat ground OK. Non-flat ground can in some cases
can make a big difference. If you want to include that parameter you
have to use different software.
There are some antennas that can't be analyzed because they exceed the
capabilities of the software. For example: Some new hams like to make
40 meter dipoles by winding a lot of wire on a broomstick. For an
accurate answer, that coil has to be modeled as a physical model, not a
lumped component model. The physical model won't work because it
exceeds the close-wire-spacing requirement of EZNEC. So you are left
with an antenna that can't be analyzed. You have to be able to
recognize these situations.
NEC only provides an estimate of the results, but it is a very good
estimate. It is not 100% accurate, but it is good enough for ham use,
and in many cases the accuracy exceeds the accuracy that you can measure
by experiment.
Jerry, K4SAV
K4SAV wrote:
>Those numbers I gave don't include all those variables. Some of the
>variables like ground quality were included as a average value. Those
>last models do not include all the possible variables because I don't
>know what each person has. Once you know that, then the model can be
>modified to include those other items. If you locate a large tower
>directly behind any of these antennas they will not perform the same.
>Exactly what that item is can change the results by a large amount.
>This is not a typical situation so it is not analyzed as typical,
>however the model can be modified to include it.
>
>Knowing what items effect the performance and when those items should be
>included into the model is all a part of learning how to use the
>software. Another item which also have to be learned is how to test the
>results to make sure you haven't exceeded the capability of the analysis
>tool. These two items are also the area where most people misuse the
>software.
>
>Jerry, K4SAV
>
>Richards wrote:
>
>
>
>>That places a lot of faith in the modeling software. How does one
>>know that sort of faith is warranted, given the number of variables that
>>can alter the results in reality? How does the modeling program account
>>for, and accommodate, all those variables? How do we know the
>>modeling is really accurate in all real life situations? Won't the real
>>situation contain variables, such as different soil and humidity
>>conditions, for example, and other differences different locations
>>present?
>>
>>(Not an argument, a legitimate and serious real question.)
>>
>>/////////////// Thanks -- K8JHR ///////////////
>>
>>=================================================
>>
>>K4SAV wrote:
>>
>>
>>
>>>If you model these antennas you can go thru a lot of configurations
>>>in a lot less time than it takes to build one and try to evaluate it.
>>>
>>>
>>You can also optimize
>>
>>
>>
>>>all these parameters to produce a loop best suited for your
>>>purposes. You can't do that by obtaining testimonials,
>>>
>>>
>>==================================================
>>
>>
>>
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