OCF Dipole and Window Line Choke
 

On Jun 28, 9:26*am, Cecil Moore wrote:
dykesc wrote:
On Jun 27, 5:17 pm, Cecil Moore wrote:
Do you mind if I upload it to my web page so
everyone can take a look?

Please do Cecil. Thanks. Dykes (AD5VS)

OK, Dykes, anyone interested in downloading your
EZNEC file can do so from:

http://www.w5dxp.com/ocfv.EZ

Roy, w7el, offered to help. Did you send your .EZ
file to him by email?
--
73, Cecil, IEEE, OOTC, *http://www.w5dxp.com

Thanks for making the file public Cecil. I'll send a copy to Roy. He
said he would be tied up with field day activities through the
weekend.

73
Dykes (AD5VS)

OCF Dipole and Window Line Choke
 

dykesc wrote in news:447c037c-c3e4-4999-9eb1-
:

http://www.w5dxp.com/ocfv.EZ

I had a look at your model and couldn't make head and tail of it.

Here is a simple model of a Carolina Windom, well to the extent that it
can be guessed from the smoke and mirrors used to describe and promote
it... http://www.vk1od.net/files/CW01.EZ .

The model attempts to represent a voltage balun at the dipole feed point,
a vertical coax feedline to a common mode choke (2000+j2000) and then the
coax outer is grounded via a moderately good station ground (directly
under the feedpoint). The power lost in the ground connection and the
choke can be found from the reports. The model does not attempt to
represent the differential mode transmission line, though it could be
done. The CW's voltage balun at the feedpoint is modelled as a pair of
equal voltage sources, with the common mode path connected between them.
I have treated the voltage balun as having zero common mode impedance, it
is probably a few ohms, but insignificant in this model.

As Roy I think already advised you, you have to model the entire common
mode path to ground and my example above is a simple one, but it
demonstrates a technique.

You will see the currents flowing in the three conductors (each side of
the dipole and the coax outer), and their contribution to / effect on the
pattern.

Others may disagree with my representation of the Carolina Windom.

Owen

OCF Dipole and Window Line Choke
 

On Jun 28, 4:51*pm, Owen Duffy wrote:

I had a look at your model and couldn't make head and tail of it.

Owen, maybe the following description will help with understanding my
model.

The antenna is an OCF Dipole in a Vee configuration. Wires 1 and 3 are
the short and long sides respectively. Wire 4 is just a short
connector at the apex. The antenna is fed with 100 feet of 450 ohm
line which transitions through a 4:1 transformer to 5 feet of 50 ohm
coax and then to the source. Wire 6 is an attempt to simulate the
unbalance radiation from the 450 ohm line. Wire 7 is an approximate
80m 1/4 wave RF "sink" on the ground side of the source end of the
model and is not meant to be a main element radiator so its position
relative to the other elements is immaterial.

Also, as you can see, I have wire 6 grounded which isn't actually the
case in the physical world. It is meant to simulate radiation from the
450 ohm line which actually ties into the 200 ohm (ungrounded high Z
side) of the transformer. I guess I figured grounding it was the right
thing to do since the EZNEC Help file implies the need for that to
simulate coax radiation. I do have wire 6 positioned correctly
relative to the other antenna elements, so its effect on the antenna
pattern should be accurate.

Don't let short wire 5 which looks out of position throw you. It just
serves as a termination junction between the 50 ohm side of the
transformer and the short run of coax. There are a couple of other
short "junction only" wires in the model.

A look at the wires, transmission lines, transformers, and sources
tables should aid in understanding the model.

I by no means mean to imply I've modeled everything correctly. I just
wanted you to know what I was attempting when I built the model.

Thanks for the Carolina Windom model. Good reference for comparing to
what I have done.

Also, thanks for looking at this. Any advice much appreciated.

73

Dykes (AD5VS)

OCF Dipole and Window Line Choke
 

dykesc wrote in news:6c2bff9b-583d-4eb5-90fb-
:

You have two parts to your model, and they are disconnected (apart from
conductor coupling effects). You have complicated your model with your
counterpoise concept and it doesn't work.

Try a simple model with not more elements than necessary, then when you
have it working, current look rational etc, extend the model.

Hint: the TL element models the differential mode of the transmission line,
and NOT the common mode. To answer your original question, you do not need
to model differential mode TL, just put the source(s) up in the centre of
the dipole.

You do need to know the common mode impedance of your 4:1 transformer to
include it in the model. If it is a voltage balun, you can probably treat
it as zero ohms without introducing great error, but if it is a current
balun (as your mention of choke implies), you need to know its impedance at
the model frequency.

Owen