Re: antenna impedance - calculated 10 - 20 Ohms - measured 36 Ohms??
- From: "David G. Nagel" <nagel@xxxxxxxx>
- Date: Mon, 27 Feb 2006 13:36:55 -0600
dansawyeror wrote:
All,Dan;
This is an attempt to add loaded radials to a loaded vertical. The plan is to make a large efficient loading coil for the radials and offset the variable coil in a 'screwdriver' vertical segment.
The antenna is about 4 meters overall with about an load at about 1.5 meters from the base. The antenna is raised about a meter.
The loaded radials are two 1 inch copper tubes about 1.67 meters long. The radial loading coil is connected from the coax shield to the radial coil.
The feed is 50 Ohm coax, the shield is connected to the loading coil and the center to the base.
4nec2 predicts an impedance of between 10 and 20 ohms depending of the assumed values of R in the impedance loads. The actual antenna measures 36 Ohms at the feed.
The question is: What is the basis of the difference between predicted and measured values?
Below is a representation of the nec code used to simulate the antenna.
Thanks - Dan
CM 75 m Vertical 12 ft high
CM base 3 ft up - two radials
CM copper conductivity
CE
GW 1 11 0 0 1 0 0 5 0.025
GW 2 7 0 0 1 0 1.67 1 0.025
GW 3 7 0 0 1 0 -1.67 1 0.025
GE 0
LD 4 1 1 1 5 1500
LD 4 1 6 6 8 600
EX 0 1 2 0 1 0
GN 2 0 0 0 13 5.e-3
FR 0 1 0 0 3.74 0
EN
I can't answer you question except to note that this is why they call antenna design an ART not a SCIENCE. Other comm enters have good suggestions. Let us know what happens.
Dave WD9BDZ
.
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- antenna impedance - calculated 10 - 20 Ohms - measured 36 Ohms??
- From: dansawyeror
- antenna impedance - calculated 10 - 20 Ohms - measured 36 Ohms??
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