i agree with eddie,
it should be noted that these old tests that the 5/8wave bandcampers talk about are ground mounted over an extensive radial system @ low frequencies with the dominant lobe been the lower lobe, not elevated a short distance above ground with 4 x 1/4wave radials @ 11mtrs + mast/feedline and the dominant lobe been the higher angle lobe,
i don't know where the idea for the equivalent length of a hat came from but there is more to it than adding the length of one hat spoke to the element,
if you remove the hat from a i-10k and retune you will end up over .6346wave as eddie claims,
something else to think about,
Method of Moment Proofs
"The moment method proof, however, is not applicable in all cases or array designs. For instance, arrays utilizing top-loading, sectionalized elements, or folded unipoles (i.e. skirted towers) must go the traditional route. In addition, shunt-fed elements also preclude the use of the method of moments. Therefore, the use of this process is more or less limited to the run of the mill "traditional" designs."
from wiki
NEC versions
There are at least four versions of NEC, with NEC-2 emerging in 1981 and NEC-4 appearing in 1992. NEC-2 is the highest version of the code within the public domain without license. NEC-4 remains proprietary with the Lawrence Livermore National Laboratory and the University of California.
NEC-4 currently requires a separate license for use. The licensing details are available from Lawrence Livermore National Laboratory here.
MININEC was a version first written in BASIC for home computers. It first emerged in 1982 on the Apple II computer. MININEC computational engines are now written in FORTRAN to improve speed. MININEC is an independent implementation of the method of moments. The basic algorithms are based upon the advice of Professor Wilton at the University of Mississippi (now with the University of Houston).
MININEC suffers from some known flaws compared to NEC, the best known being that resonant frequencies may be slightly in error. However, MININEC handles different wire diameters better than NEC2 and probably NEC4[1]; this includes different diameter parallel wires, different diameter wires joined at an angle, and tapered diameter antenna elements. Placing sources at an intersection of two wires is a problem for NEC2 but not MININEC[2]. MININEC converges more slowly (requires more segments) when wires join at an angle, when wire segments of significantly different length are adjacent, and has a weaker ground model[3].
[edit] NEC in the field
Although antennas can be simple structures, the modeling of these systems does require a certain level of understanding of the electrical characteristics of antennas.
As a starter for any modeler, 4nec2 or EZnec can be used. See their respective home pages for further information on their purchase and/or installation.
[edit] Limitations
- NEC-2 does not model tapered elements such as those made of telescoping aluminum.
- NEC-2 does not model buried radials or ground stakes.
[SIZE=+1] [/SIZE]eznec.com
Does EZNEC v. 5.0 use NEC-4 for calculations?
Of the five EZNEC v. 5.0 program types (demo, standard EZNEC, EZNEC+, EZNEC Pro/2, and EZNEC Pro/4) only EZNEC Pro/4 uses NEC-4. NEC-2 is the calculating engine used by the other EZNEC programs. See the next item, below, for more information.
There are two professional (EZNEC Pro) programs, EZNEC Pro/2 and EZNEC Pro/4. They are identical except that EZNEC Pro/4 can use NEC-4 for calculations as well as the NEC-2 used by the other EZNEC program types.
The primary advantages of NEC-4 are that buried conductors can be modeled, and NEC-4 is relatively free of the small error produced by NEC-2 when analyzing connected wires of different diameters.
