On Tue, 07 Mar 2006 14:18:47 -0500, Michael Coslo
wrote:

....

My setup is:

Icom IC-761
Antenna 1 - Homebrew OCF dipole at ~ 50 feet.
Antenna 2 - Butternut HF6V -ground mounted and 18 radials on the ground.


Question, does the magnitude of feedline radiation from the OCF
(presumably predominantly vertical) significantly affect qualification
of it as a horizontal antenna?

There shouldn't be any feedline radiationn, this is oan antenna
running coax to a 4:1 balun at the feedpoint.

Mike, I understand that feedline radiation is an un-escapable
characteristic of an OCF dipole, caused by the asymmetric feed. Some
even claim it as a major advantage (eg Caroline Windom). Whilst no
dipole is perfect in that respect, the OCF dipole is less perfect, and
it may be worth modelling the thing to comment in your findings on the
probably magnitude of the contribution by the feedline.

Great project, look forward to follow-ups.

Owen
--

On Tue, 07 Mar 2006 14:18:47 -0500, Michael Coslo
wrote:

Question, does the magnitude of feedline radiation from the OCF
(presumably predominantly vertical) significantly affect qualification
of it as a horizontal antenna?

There shouldn't be any feedline radiationn, this is oan antenna
running coax to a 4:1 balun at the feedpoint.

Hi Mike,

Not all 4:1 BalUns exhibit enough (or sometimes any) common mode Z.

73's
Richard Clark, KB7QHC

Hmmm... Gee, I could connect a spectrum analyzer channel to each of
two different antennas and get a continuous real-time comparison of the
signals and noise them.

Cheers,
Tom

Richard Clark wrote:
On Tue, 07 Mar 2006 14:18:47 -0500, Michael Coslo
wrote:

Question, does the magnitude of feedline radiation from the OCF
(presumably predominantly vertical) significantly affect qualification
of it as a horizontal antenna?
There shouldn't be any feedline radiationn, this is oan antenna
running coax to a 4:1 balun at the feedpoint.

Hi Mike,

Not all 4:1 BalUns exhibit enough (or sometimes any) common mode Z.

Okay. Perhaps I might better characterize my experiment as a comparison
of a vertical and an OCF dipole of indeterminate vertical vs horizontal
performance. I was under the impression from the designers of this
flavor of dipole that they were not radiating from the feedline unless
you wanted that "feature". In that case you would feed the antenna with
balanced line. Certainly the antenna doesn't seem to be radiating RF
from anywhere but the antenna bits.

p.s. forgive the spelling, I am using a beta of Thunderbird for my
newsgroups, and it seems to have a few quirks that make it hard to see
what I have written!!

- 73 de Mike KB3EIA -

On Wed, 08 Mar 2006 09:47:18 -0500, Michael Coslo
wrote:

I was under the impression from the designers of this
flavor of dipole that they were not radiating from the feedline unless
you wanted that "feature".

It is pretty well known that an OCFD is a bear when it comes to common
mode current on the feedline. Usally requiring more than one common
mode choke to tame the sucker.

Danny, K6MHE

On Wed, 08 Mar 2006 09:47:18 -0500, Michael Coslo
wrote:

I was under the impression from the designers of this
flavor of dipole that they were not radiating from the feedline unless
you wanted that "feature".

Hi Mike,

This is not outside the realm of possibility. Whose antenna is it?

73's
Richard Clark, KB7QHC

Michael Coslo wrote:
Okay. Perhaps I might better characterize my experiment as a
comparison of a vertical and an OCF dipole of indeterminate vertical vs
horizontal performance. I was under the impression from the designers of
this flavor of dipole that they were not radiating from the feedline
unless you wanted that "feature".

Unfortunately, even if the designers don't intend the feedline to
radiate, it's very difficult to avoid. A single balun at the feedpoint
is very likely not enough to prevent it.

In that case you would feed the
antenna with balanced line.

That would make no difference at all in determining whether or not the
line would radiate.

Certainly the antenna doesn't seem to be
radiating RF from anywhere but the antenna bits.

The amount of feedline common mode current and therefore radiation will
vary from band to band, probably a great deal. It's easy enough to make
up a simple current probe with a clamp-on core and make quantitative
measurements if you're interested. They've been described on this
newsgroup several times.

Roy Lewallen, W7EL

Radiation from feedlines is grossly exaggerated.

For many purposes, practically it does not occur.

When discussing the importance of such radiation one should always
crudely estimate its level relative to transmitter or radiated power.

If you don't know what its level is then you don't know what you are
waffling about.
----
Reg.

On Wed, 8 Mar 2006 21:55:42 +0000 (UTC), "Reg Edwards"
wrote:

If you don't know what its level is then you don't know what you are
waffling about.

Hi Reggie,

Seeing you lack any quantifiables, are you offering belgian waffles?

73's
Richard Clark, KB7QHC

On Wed, 08 Mar 2006 13:58:19 -0800, Richard Clark
wrote:

On Wed, 8 Mar 2006 21:55:42 +0000 (UTC), "Reg Edwards"
wrote:

If you don't know what its level is then you don't know what you are
waffling about.

Hi Reggie,

Seeing you lack any quantifiables, are you offering belgian waffles?

73's
Richard Clark, KB7QHC

Richard,

Just anouther one of Reg's factoids (e pluribus unum).


Danny