Microbit RRC-1258 MkII(s) Manual de usuario descargar pdf (Pagina 13)

Antenna Modelling

The Cond (Ground Conductivity) and Diel Constant in the

sample model are set to those for very good ground. To make the

model more realistic we will

change these parameters to

those for average ground.

Change the Cond

(Conductivity) value from

0.0303 to 0.005 Siemens per

metre. Change the Diel Const

(Dielectric Constant) value

from 20 to 13 – Fig 4.9. Close

the window.

This changes these

values from those for good

ground to average ground.

These may not be those

pertaining at any particular

amateur QTH, the only certain

way being to measure them.

However, an idea of the likely ground conductivity anywhere in the UK

can be obtained from Fig 4.10. Also, http://andycowley.net/ant/vmox/

gm.html has a useful colour map, showing ground conductivity in the

UK and a list of permittivity values for various soil types.

Commonly accepted values for conductivity and permittivity values

for good, average and poor ground are shown in Table 4.2.

Table 4.2:

Typical ground

parameters.

Ground Conductivity Conductivity Permittivity

Type (Siemens/m) (Milli-Siemens/m)

Poor 0.001 1 5

Average 0.005 5 13

Good 0.0303 30.3 20

Click on the Wire Loss button, click on

the copper button to change from zero loss

– Fig 4.11. Click OK to close the window.

We are using copper wire and the resistive

loss needs to be taken into account in

calculating the actual antenna gain. Click OK

to close the window.

Click on the Plot Type button and

change from elevation to 3D by clicking on

the 3D button – Fig 4.12 (overleaf). Click OK

to close the window.

Fig 4.9: The

Ground

Description

Window for the

G5RV.

Fig 4.10: Ground

Conductivity Map

for the UK. The

values are in

milli-Siemens

per metre.

Fig 4.11: Wire

Loss window for

the G5RV.

1 2 ... 8 9 10 11 12 13 14 15 16 17 18 ... 29 30

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