Microbit RRC-1258 MkII(s) Manual do Utilizador descarregar pdf (Página 11)

Antenna Modelling

example models. Left click on this, then click ‘Open’. The Control

Centre window reveals we have opened the model file BYDipole.EZ

which is a ‘Back yard Dipole’ for 20 metres at a height of 30ft.

Click ‘Wires’, which opens the Wires definition window – Fig 4.3.

The single wire dipole is defined as a wire with End 1 and End 2 xyz

co-ordinates. The wire is 12 gauge bare copper and is 33.43 feet long

at a height of 30ft with 11 segments. The Wires window is where the

antenna to be modelled is defined as a series of wires. We will be

using only one wire, but more complex models will need many wires

and it can be a tedious process to correctly define all of them. Certain

tools are provided under the Create function to more easily define

structures like radials, loops and helixes.

Note the last two columns, dealing with insulation. This allows

antennas with plastic coated wires to be modelled. The effect of the

coating is to slightly shorten the required wire lengths compared to

bare copper.

We will now turn this 20m dipole into a 102ft G5RV dipole, made

of copper wire, 0.1-inch diameter, complete with a 20m λ/2 feed stub

made of 450-ohm open wire feeder. We will then examine the radiation

plots and feed-point impedances at the bottom of the feeder.

Fig 4.4 shows the Wires window, modified to create the model of

the G5RV.

We have changed the length to 102 ft, the number of segments

to 51 (19 if using the free demo version)and the wire diameter to 0.1-

inch. To change these parameters, simply highlight each value to be

changed and type in the new value. Close the window when finished.

The new values are automatically saved.

Note we have used an odd number of segments. This is neces-

sary with NEC2, to allow connection of feed points, or in this case

transmission lines to the exact centre of the dipole.

We will now add a 20m λ/2 450-ohm ladder-line in the Transmis-

sion Lines Window. We need a half wave long line at 14.175MHz

made from 450-ohm ladder line with a Velocity Factor of 0.9. This is

32.23 feet long. Real life transmission line losses are 0.082dB per

100ft at 10MHz.

Fig 4.3: The

Wires Window

for BYDipole.

Fig 4.4: The

Wires Window

edited for the

G5RV. If the Free

Demo version is

used, the number

of segments

should be 19.

1 2 ... 6 7 8 9 10 11 12 13 14 15 16 ... 29 30

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