I highly recommend that you decouple the feedline with a current balun
(common mode choke). Better yet would be two, spaced about a quarter
wavelength apart. Small antennas can be made to look a lot better than
they really are if the feedline is allowed to become part of the
radiating antenna system, so unless the feedline is decoupled well, any
measurements you make will be subject to speculation as to whether the
radiation was from the antenna or the feedline.

Roy Lewallen, W7EL

Denny wrote:
Art did ship me one of his antennas a week or two back... I have it in
my shop...
I will indeed put this interesting antenna to an objective and
thorough testing with a full report here... I am always excited to
learn something new...

It is 19F outside this morning and blowing hard, with wind and snow
forecast through the week and into the weekend, and I am unlikely to
climb the big tower in this...
I will attempt within a week to put it on a small 50' tower I have
attached to my shop and get some baseline impedence and field strength
measurements... Then as soon as the weather allows I will move it to
the big tower for a good test against my full size antennas...


I am sorry to have to put this off a bit, but given the weather and
that my family is hurting at the moment my free time is limited...

denny / k8do

Roy Lewallen wrote:
I highly recommend that you decouple the feedline with a current balun
(common mode choke). Better yet would be two, spaced about a quarter
wavelength apart.

Methinks if Denny does that, Art should have used
bigger wire for his coil.
--
73, Cecil http://www.w5dxp.com

In article ,
Roy Lewallen wrote:

I highly recommend that you decouple the feedline with a current balun
(common mode choke). Better yet would be two, spaced about a quarter
wavelength apart. Small antennas can be made to look a lot better than
they really are if the feedline is allowed to become part of the
radiating antenna system, so unless the feedline is decoupled well, any
measurements you make will be subject to speculation as to whether the
radiation was from the antenna or the feedline.

It would also be interesting to use a simple current probe to sweep
along the feedline, and see what sorts of currents might be flowing
along the outside of the feedline, both with and without a good
common-mode choke or two in the feedline.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

On Mar 5, 3:14 pm, (Dave Platt) wrote:
In article ,
Roy Lewallen wrote:

I highly recommend that you decouple the feedline with a current balun
(common mode choke). Better yet would be two, spaced about a quarter
wavelength apart. Small antennas can be made to look a lot better than
they really are if the feedline is allowed to become part of the
radiating antenna system, so unless the feedline is decoupled well, any
measurements you make will be subject to speculation as to whether the
radiation was from the antenna or the feedline.

It would also be interesting to use a simple current probe to sweep
along the feedline, and see what sorts of currents might be flowing
along the outside of the feedline, both with and without a good
common-mode choke or two in the feedline.


I agree. I think it's quite possible that even a decoupled feedline
will add enough radiation to make the antenna noticeably better
than it really is.
I'd prefer to see the source mounted *at* the antenna to make it
a decent comparison.
One problem with the decoupling that I can see, is if it's used on
160m, a quarter wave is about 125-130 feet plus or minus...
So even if you stack two chokes or baluns a quarter wave apart,
I can see the feedline noticeably radiating above the lower choke.
Of course, this condition will exist for all types of antennas,
but on the other hand, most antennas will be radiating quite
a bit more from the antenna, vs the feedline.
So the difference between the two sources are much larger,
and the feedline radiation is more likely to be swamped and
made a non issue as far as the total radiation.
But with such an inefficient small antenna, the feedline
radiation will be a much larger part of the total radiation.
My guess on the performance? Probably about the
same as the usual Isotron antenna used on 160m.
And even in the case of the Isotron, I bet a good portion of
the radiation is actually from the feedline.
I don't recall ever seeing any documentation of the Isotron
that recommended decoupling the feedline.
I don't have to stretch my mind to far to wonder why... :/
To quiet the naysayers, "like me", I'd mount a radio directly
to the base of the antenna with a coax union and
do FS tests at certain distances, and then likewise
with the full size antennas.
That would cure the feedline issue real fast.. lol..
Course, that may be more work than Denny wants to
take on..
You could compare it to a mobile set up though, and
keep things on the ground level for ease of testing.
I bet my mobile antenna would whip that thing.
It should, being it's bigger and has more efficient loading.
MK

wrote:
I agree. I think it's quite possible that even a decoupled feedline
will add enough radiation to make the antenna noticeably better
than it really is. I'd prefer to see the source mounted *at* the
antenna to make it a decent comparison.
__________

Unless this antenna is itself balanced, most likely for best efficiency when
operating in this configuration there would need to be a conductor running
from the elevated tx chassis to a good r-f ground of some kind, either
buried in the earth or in the form of a counterpoise. Radiation from that
"ground" conductor could be many times greater than from what is considered
to be the antenna -- even though no feedline is present..

This is a common configuration used for so-called Part 15 AM installations
to get greater groundwave coverage from the 100 mW tx input power allowed
under FCC Part 15.219, by ignoring the 3-meter limit on the length of the
radiating structure given there.

RF

wrote:
On Mar 5, 3:14 pm, (Dave Platt) wrote:
In article ,
Roy Lewallen wrote:

I highly recommend that you decouple the feedline with a current balun
(common mode choke). Better yet would be two, spaced about a quarter
wavelength apart. Small antennas can be made to look a lot better than
they really are if the feedline is allowed to become part of the
radiating antenna system, so unless the feedline is decoupled well, any
measurements you make will be subject to speculation as to whether the
radiation was from the antenna or the feedline.
It would also be interesting to use a simple current probe to sweep
along the feedline, and see what sorts of currents might be flowing
along the outside of the feedline, both with and without a good
common-mode choke or two in the feedline.


I agree. I think it's quite possible that even a decoupled feedline
will add enough radiation to make the antenna noticeably better
than it really is.
I'd prefer to see the source mounted *at* the antenna to make it
a decent comparison.

But if the major radiation is from the feedline, that will mean the
antenna won't work as it is supposed to.

Since this is voodoo antennaland stuff, the antenna needs to be tested
as Art would suggest, not as we might like. And since most of the chaps
here are a lot smarter than me, I suspect everyone knows that his
antenna just might need that feedline radiation in order to work "properly".

Now after the initial tests in whatever manner Art dictates, *then* the
feedline should be isolated to determine where the major radiation is
coming from.

At that point, your source at the antenna method is the ticket. That
would remove feedline effects altogether.

Is this test going to be written up somewhere? What is the test protocol?

- 73 de Mike N3LI -

Denny wrote:
Art did ship me one of his antennas a week or two back... I have it in
my shop...
I will indeed put this interesting antenna to an objective and
thorough testing with a full report here... I am always excited to
learn something new...


Hi Denny,


What is the test protocol that you are using?


- 73 de Mike N3LI -

wrote:
On Mar 5, 3:14 pm, (Dave Platt) wrote:
In article ,
Roy Lewallen wrote:

I highly recommend that you decouple the feedline with a current balun
(common mode choke). Better yet would be two, spaced about a quarter
wavelength apart. Small antennas can be made to look a lot better than
they really are if the feedline is allowed to become part of the
radiating antenna system, so unless the feedline is decoupled well, any
measurements you make will be subject to speculation as to whether the
radiation was from the antenna or the feedline.
It would also be interesting to use a simple current probe to sweep
along the feedline, and see what sorts of currents might be flowing
along the outside of the feedline, both with and without a good
common-mode choke or two in the feedline.


I agree. I think it's quite possible that even a decoupled feedline
will add enough radiation to make the antenna noticeably better
than it really is.
I'd prefer to see the source mounted *at* the antenna to make it
a decent comparison.
. . .

Even that might not be adequate, depending on the design of the
transmitter. Any power or other wires connected to the transmitter could
easily become part of the radiator, so they'd have to be decoupled. A
small, battery-powered transmitter with no connected wires would avoid
this potential problem.

Roy Lewallen, W7EL

Michael Coslo wrote:

But if the major radiation is from the feedline, that will mean the
antenna won't work as it is supposed to.

Since this is voodoo antennaland stuff, the antenna needs to be tested
as Art would suggest, not as we might like. And since most of the chaps
here are a lot smarter than me, I suspect everyone knows that his
antenna just might need that feedline radiation in order to work
"properly".

Now after the initial tests in whatever manner Art dictates, *then* the
feedline should be isolated to determine where the major radiation is
coming from.

At that point, your source at the antenna method is the ticket. That
would remove feedline effects altogether.
. . .

Fair enough. But only the naive will be impressed by an antenna system
that has to be electrically large (including the feedline) in order to
be efficient, unless it also has some property that's significantly
different than the radiating feedline alone. For example, it would be
interesting if it's highly directional when fed with a vertical
feedline, but not if it just looks like another vertical.

If the feedline is radiating, you can expect the antenna performance to
be quite sensitive to the conductive path from the transmitter to the
Earth, as well as the feedline length and orientation. Consequently,
different people will likely get considerably different results, even
with identical antennas and feedlines. So the entire path from the
transmitter to the Earth will have to be specified and carefully
duplicated in order to get meaningful and repeatable results if the
feedline is a critical part of the system.

Roy Lewallen, W7EL

On Mar 5, 3:23 am, wrote
..
Does this help clarify my stance on this small sized subject?
I try to avoid any gray areas that might give the impression
that I think this device even has a remote chance of it's
claimed full sized success as a radiator of RF.
But in case some still get confused by what I say, let me
rephrase in a manner that most all will understand.
What a load of horse manure says I...
MK


Spoken like a true neanderthal, they also refused to embrace new ways
of doing things and look what happened to them.
You are living in the past, keep on digging.

Derek