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ANTENNAS FOR 100 POUND DXPEDITIONS 6.4

Force-12 Sigma-5 on 15 meters The match on 15 meters is under 2:1 for the entire band with the dip just before the center of the band. We must remember that these numbers are for the model of the antenna (but the model’s predictions have been verified by direct measurement). -------------- LOADS (RLC Type) -------------No.

Specified Pos. Wire #

Actual Pos.

% From E1

% From E1

Seg

L

C

(ohms)

R

(uH)

(pF)

R Freq (MHz)

Type

1

2

47.00

47.73

11

Open

1.21

Open

21.2

Par

2

2

55.00

56.82

13

Open

1.21

Open

21.2

Par

3

2

50.00

52.27

12

Short

0.52

Short

0

Ser

SWR predicted by model

SWR measured by AntennaSmith

Figure 54 SWR for Force-12 Sigma-5 on 15 meters Though this antenna is relatively short for a 15 meter antenna the resistance presented is still relatively high. Assuming all this resistance is not losses, why would the radiation resistance be so high? Consider the surface area of a 16 AWG wire. The diameter of this wire is about 0.05 inches. The circumference is therefore just under 0.08 inches (0.05/2 * pi). The circumference of the one inch aluminum pipe is 1.57 inches. That is nearly 20 times the surface area of the wire! That is much more metal to radiate.

51

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Antennas for 100 Pound DXpeditions - volume 1  

Computer-based antenna modeling and direct experience with lightweight portable antenna systems. Volume 1: Selected high band antennas [20-6...

Antennas for 100 Pound DXpeditions - volume 1  

Computer-based antenna modeling and direct experience with lightweight portable antenna systems. Volume 1: Selected high band antennas [20-6...

Profile for ne1rd
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