Follow up:

One of the not so apparent results of Reg's program is the relationship of
radial length to height. I chose 2 meters because they were only .7 meters high.

I raised your model to 2 meters, that reduced the R to about 20 Ohms. Raising it
to 3 meters lowers it to 18 Ohms.

How did you calculate the H of the loading coils? Is that easy to edit? It would
seem that these values are closer.

Dan

Frank's Basement 2 wrote:
Hi Dan, thanks for the interesting info. You did not specify dimensions,
but from your comments it appears you are using a vertical about 23 ft high.
Such a monopole would have a 3.5 ohm input impedance when placed above a
perfectly conducting ground, and gain about +4.5 dBi. Adding a center
loading coil raises the input impedance to 11.5 ohms, and gain +2.6 dBi.
Base loading provides an input impedance of 5.5 ohms with almost the same
gain as center loading (Q = 400). Adding ten, 6ft radials, at 3" above an
average ground, the input impedance increases to 40 ohms, and gain -6.3 dBi.

Adding lumped element loading coils, (75 uH, Q = 400) in each radial
(antenna base end) drops the input impedance to 37 ohms, and gain -6.4 dBi.
Don't know why this does not agree with Reg's program. Probably I made some
fundamental error with the NEC model. Included the code below, so you may
see an error I missed.

73,

Frank

CM 75 m Vertical 23 ft high
CE
GW 1 64 0 0 23 0 0 0.25 0.0026706
GW 2 12 0 0 0.25 6 0 0.25 0.0026706
GM 1 9 0 0 36 0 0 0 002.002
GS 0 0 .3048
GE 1
GN 2 0 0 0 13.0000 0.0050
EX 0 1 64 0 1.00000 0.00000
LD 5 1 1 184 5.8001E7
LD 4 1 33 33 4 1600
LD 4 2 1 1 4 1750
LD 4 3 1 1 4 1750
LD 4 4 1 1 4 1750
LD 4 5 1 1 4 1750
LD 4 6 1 1 4 1750
LD 4 7 1 1 4 1750
LD 4 8 1 1 4 1750
LD 4 9 1 1 4 1750
LD 4 10 1 1 4 1750
LD 4 11 1 1 4 1750
FR 0 11 0 0 3.5 0.05
RP 0 181 1 1000 -90 0 1.00000 1.00000
EN





Frank,

Good morning. Let me start at the beginning. I have a loaded vertical on

75

meters. The combination of the antenna and ground measure about 40 Ohms at

the

antenna. The models all show such an antenna over a perfect ground should

have a

radiation resistance of between 3 and 4 Ohms. That says the antenna system

is

less the 10% efficient.

This then is a journey to reduce ground resistance. Attempts to add

radials and

wire mesh to the ground have had very little if no effect. This leads to

Reg's

c_poise model. It predicts a coil in the range of 60 uH to 90 uH tuned to

a 2

meter by 18 mm 'wire' will have a total resistance in the 2 to 4 Ohms

range.

Together this should result is a 8 Ohm system. The ratio can be directly
inferred as an performance improvement of 5 to 1 or 7 db. This is worth

some

effort.

To answer your question the first step will be one coil and one radial.

The

objective is the get the antenna system close to 10 Ohms. From there I

will

experiment with adding radials and coils. I am not sure what to expect.

Thanks - Dan





Frank wrote:

Not sure I understand what is going on Dan. Are you planning on loading
each radial element?

Frank


"dansawyeror" wrote in message
...


These results were from Reg's c_poise program. The band is 75 meters and
the coils were about 70 uH. The coils were a relatively large diameter,

on

the order of a meter. The wire lengths were about 20 meters. By varying
the length the coil, the coil wire may be varies from 1mm to 12mm.

Richard Clark wrote:


On Sat, 18 Feb 2006 08:20:38 -0800, dansawyeror
wrote:




The devil is in the details. Modeling shows large coils with 1 mm wire
have a Q in the range of a few hundred. On the other hand a coil with

12

mm tubing has a Q of about 2000. The R of the 1 mm coil is about 6

Ohms

while the 12 mm coil is on the order of 1 Ohm.

Given these model results it says there is a significant difference
between 1 mm and 12 mm coils.


Hi Dan,

In the details, indeed. What is the LENGTH of wire in this 6 Ohm
resistor? What is the LENGTH
of wire in this 1 Ohm resistor? How many turns are in these "large
coils?" What is their diameter? What is their solenoid length?

Without these details, there is nothing said that is significant.

73's
Richard Clark, KB7QHC