Re: Problem with nec2

"Detlef Conradin" <skyline@xxxxxxxxxxxxx> wrote in message
news:436125c1$0$1163$5402220f@xxxxxxxxxxxxxxxxxx
> Hi
>
> To get started with nec2 I tried to simulate a simple dipole.
> The graphical view of the pattern looks okay, however the gain seems
> to be to high. To what are the DBs refered in the output file?
> Or what do I have to change to get the gain in dBi ?
>
> Here is my input file:
> -----------------------------------------
> CM Test
> CE
> GW 1 20 0 0.005 0 0 7.5 0 0.01
> GW 2 20 0 -0.005 0 0 -7.5 0 0.01
> GW 3 1 0 -0.005 0 0 0.005 0 0.01
> GE 0
> EX 0 3 1 1 10. 0 0 0 0 0
> FR 0 30 0 0 6. 1. 0 0 0 0
> RP 0 37 72 1001 0. 0. 5. 5. 1000 1.
> EN
> -----------------------------------------
>
> Detlef
>
> PS:
> If I calculate the gain with the formula:
>
> 4 * Pi * r^2 * |E|^2
> Gain = -----------------------
> P_in * 2 * 120 * Pi
>
> by using the E-Field magnitude values from nec2's output I get also
> those very high values. (?)
>

Hi, you have a segment length violation in TAG 3; it is very short, being
only 5mm. Also short when compared to the segment length in TAGs 1 and 2
at 37.5 cm. It is a good idea to maintain equal segment lengths in the
entire model, with minimum lengths not exceeding 0.001 wavelengths on any
frequency. I have modified your code as shown below. There is nothing
wrong with breaking the wire up into three tags, but they should all run the
same way. Your end TAGs are running in opposite directions, which will
cause current discontinuities in plots, and NEC output file data.

There was something weird about your RP card also, but have not yet delved
into what is wrong. I have not checked, but your computation of gain with
the E-field should now be correct.

Cebik's book on NEC modelling, at www.nittany-scientific.com, for $50 is
well worth the money.

Regards,

Frank


CM Test
CE
GW 1 21 0 -7.5 0 0 7.5 0 0.01
GS 0 0 1.000000
GE 0
GN -1
EX 0 1 11 00 10. 0 0 0
FR 0 30 0 0 6. 1. 0 0 0 0
RP 0 181 1 0000 -90 0 1.00000 1.00000 1000 1.
EN


.

Relevant Pages

  • Re: Problem with nec2
    ... To what are the DBs refered in the output file? ... but nec2 shows the total radiated power in its output. ... > "Phi" pattern is only computed for one frequency. ... > is that I normally do not use gain averaging. ...
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  • Problem with nec2
    ... The graphical view of the pattern looks okay, ... To what are the DBs refered in the output file? ... Or what do I have to change to get the gain in dBi? ...
    (rec.radio.amateur.antenna)