Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #1   Report Post  
Old March 5th 08, 09:14 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Jul 2006
Posts: 464
Default 'SMALL' ANTENNA CRITERIA

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!
  #2   Report Post  
Old March 6th 08, 01:40 AM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Jul 2006
Posts: 757
Default 'SMALL' ANTENNA CRITERIA

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
  #3   Report Post  
Old March 6th 08, 12:07 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Jun 2006
Posts: 440
Default 'SMALL' ANTENNA CRITERIA

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

  #4   Report Post  
Old March 7th 08, 12:27 AM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Jul 2006
Posts: 757
Default 'SMALL' ANTENNA CRITERIA

On Mar 6, 6:07 am, "Richard Fry" wrote:
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


For some reason, I'd always got the impression that the antenna
was symmetrical and balanced.. But who ever knows for sure
with Art...
If this is the case, I wonder why he needs the garbage can lid, or
whatever metal he is using under it..
I had the impression in his various posts that he was trying to
avoid ground connections. But whoever knows for sure except
Art, and now maybe Denny... :/
MK
  #5   Report Post  
Old March 6th 08, 01:52 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Jun 2006
Posts: 828
Default 'SMALL' ANTENNA CRITERIA

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 -


  #6   Report Post  
Old March 6th 08, 06:55 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Jun 2006
Posts: 1,374
Default 'SMALL' ANTENNA CRITERIA

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
  #7   Report Post  
Old March 6th 08, 11:33 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Jul 2006
Posts: 274
Default 'SMALL' ANTENNA CRITERIA

Michael Coslo wrote:
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 -


Easier said than done, Mike.
73,
Tom Donaly, KA6RUH
  #8   Report Post  
Old March 7th 08, 02:02 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Jun 2006
Posts: 828
Default 'SMALL' ANTENNA CRITERIA

Tom Donaly wrote:

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

- 73 de Mike N3LI -


Easier said than done, Mike.



Any way we look at it, Tom! ;^)

- 73 de Mike N3LI -
  #9   Report Post  
Old March 6th 08, 06:45 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Jun 2006
Posts: 1,374
Default 'SMALL' ANTENNA CRITERIA

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
  #10   Report Post  
Old March 6th 08, 11:29 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Mar 2007
Posts: 36
Default 'SMALL' ANTENNA CRITERIA

On Mar 7, 3:45 am, Roy Lewallen wrote:
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



You still don't understand! you are talking bull**** you have no
idea of the design of Art's antenna or of how it works or it's needs
yet you put up your remedies for old style antenna's.

I am sure Denny is a competent and independant operator and will be
aware of all the pitfall's of testing a new antenna and does not need
you to tell him how to go about it.
As Art said in a previous post Denny is free to do as he wishes Art
will have no input in the testing of the antenna, and nor should you

Keep on digging the hole is getting bigger.

Derek




Reply
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules

Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
constrained listening criteria: tom k in L.A. Shortwave 1 January 17th 07 01:49 PM
A Small Indoor FM Antenna W. Watson Antenna 4 March 27th 06 06:02 PM
Good Small Antenna David CB 5 December 29th 03 03:09 PM
Common Criteria Bill Shell Swap 0 December 28th 03 07:49 PM
Small Directional Antenna Ron Antenna 5 September 4th 03 12:04 AM


All times are GMT +1. The time now is 04:58 PM.

Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
Copyright ©2004-2025 RadioBanter.
The comments are property of their posters.
 

About Us

"It's about Radio"

 

Copyright © 2017