"dansawyeror" wrote in message
...
All,

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

Interesting Dan, I get the same results as you, using your code. At 3.74
MHz the input z is 16.8 +j133. The antenna is resonant at about 3.55 MHz.
With your average ground the gain is about -9 dBi.

The only question I have is how certain are you of the accuracy of your test
equipment? Did you use a 1:1 balun at the feed point? You may be getting a
large current on the outside of the coax.

Frank