Re: NEC-LIST: NEC-4 problem with salt water ground

I have also found problems with NEC 4 for the case of a small loop
over sea water.

See Attached file.

This Technical Correspondence was published, see:

Belrose. J.S., "Performance of antennas close to the ground", RadCom,
November 2005, pp. 80-83.

If you get into problems use NEC-2, is the conclusion I came to.

73, Jack, VE2CV

>I recently ran into an example of an apparent problem with NEC-4
>using salt water ground characteristics (conductivity = 5 S/m, rel.
>permittivity = 81), where it gives a negative input resistance for a
>single-source model. NEC-2 gives a believable positive resistance
>for the same model. Here's the model:
>
>CE
>GW 1,21,0.,-15.5448,15.24,0.,0.,15.24,.0008138
>GW 2,21,0.,0.,15.24,0.,15.5448,15.24,.0008138
>GW 3,21,0.,0.,15.24,0.,0.,.1524,.0008138
>GW 4,21,0.,0.,.1524,0.,50.292,.1524,.0008138
>GW 5,21,0.,0.,.1524,0.,-50.292,.1524,.0008138
>GE 1
>FR 0,1,0,0,1.83
>GN 2,0,0,0,81.,5.
>EX 0,3,21,0,1.,0.
>XQ
>EN
>
>The result using NEC-4 is an impedance at the source of -61.4 + j621
>ohms. NEC-2 reports a believable 14.8 + j105 ohms.
>
>The problem with NEC-4 is evidently the combination of highly
>conductive ground and the low (0.0009 wavelength) radial wires,
>since raising the radials or decreasing the conductivity restores
>apparently valid operation.
>
>I recall from some past experience and correspondence that NEC-4
>isn't nearly as tolerant as NEC-2 of extreme ground conductivities.
>But it was some time ago and I haven't been able to locate the
>information. Can anyone shed some light on what guidelines should be
>followed to avoid this problem?
>
>Thanks,
>Roy Lewallen
>
>--
>The NEC-List mailing list
>NEC-List_at_robomod.net
>http://www.robomod.net/mailman/listinfo/nec-list

-- 
John S. (Jack) Belrose, PhD Cantab
Life Senior Member of the IEEE
TA ARRL, Fellow Radio Club of America
Member AWA, Life Member QCWA
Radioscientist Emeritus Researcher
Communications Research Centre Canada
PO Box 11490 Stn H
OTTAWA   ON   K2H 8S2
CANADA
e-mail  john.belrose_at_crc.ca
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