To All from PA0SE
Some time ago you received via the reflector the following correspondence
between PA0SE and W7EL.
-----Oorspronkelijk bericht-----
Van: Roy Lewallen <[email protected]>
Aan: Dick Rollema <[email protected]>
Datum: dinsdag 20 juli 1999 19:35
Onderwerp: Re: Antenna Software
Dick,
Only the professional versions of EZNEC (EZNEC-M and EZNEC/4) directly
report the ground wave. However, a reasonable approximation of the
ground wave field strength can be gotten by using the EZNEC near field
analysis. This is because the "near field" analysis actually calculates
the total field, both near and far, including the ground wave. The near
field analysis results are available only as numbers; they are not
plotted as a graphical pattern.
Roy Lewallen, W7EL
Dick Rollema wrote:
Dear Roy,
Quite a few countries in Europe now have made the 136 kHz longwave
band available to amateurs.
Although at night some sky wave propagation may be present most of the
contacts are made via the so called surface wave.
I wonder whether EZNEC and ELNEC produce proper radiation patterns for
that kind of wave propagation?
73, Dick, PA0SE
I use the antenna simulation program Antenna Optimizer by Brian Beezley,
K6STI.
This program also has the possibility to compute the near field and I
wondered whether this was also suitable for computing the field strength of
the surface wave.
I modelled my antenna system and let the computer calculate the electric and
magnetic component of the field. As Roy explained this must the total field,
near plus far.
For antennas on the surface of the earth outside the near field region only
the surface wave remains.
Only in the far field E/H = 377, in which E = electric component in V/m and
H = magnetic component in A/m. So this is a method to check whether you are
in the far field region or not.
For several distances (in metres) from the antenna I found the following:
Distance E/H
500 271
1000 338
1500 358
2000 366
2500 369
3000 371
3500 374
4000 375
This shows that my earlier statement is correct: in order to obtain the
EIRP of a transmitter by measuring the field strength with a loop (or
ferrite rod) antenna a minimum distance of 3500 m is sufficient for a
meaningful result.
73, Dick, PA0SE
JO22GD
D.W. Rollema
V.d. Marckstraat 5
2352 RA Leiderdorp
The Netherlands
Tel. +31 71 589 27 34
E-mail: [email protected]
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