LinkBack Thread Tools Search this Thread Display Modes
Prev Previous Post   Next Post Next
  #21   Report Post  
Old April 3rd 08, 06:12 AM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Mar 2008
Posts: 1,339
Default Antenna physical size

On Apr 2, 10:37 pm, wrote:
On Apr 2, 1:41 pm, Art Unwin wrote:



Pray tell me then why I am incorrect. You can salvage the
answer from your own mind or even from a book.
When the air breaks down around an antenna it is because the antenna
is not in a state of equilibrium.


Define equilibrium as it pertains to an antenna. Until you do, it's
fairly hard to comment on the first statement.


I don't think I can do that for you, it would take to long.

If you have corona discharge from an antenna, it's usually due
to sharp points when using wire or a whip with a pointed tip.
Thats why they stick round balls on whips, flagpoles, etc..


When you have a discharge it is a loss of energy

When a dipole is replaced by a quad ala
a series circuit is replaced by a tank circuit it clearly shows that
the latter is more efficient.


What clearly shows this?

Well there is no discharge. This is becaquse that there is a route
of a lesser impedance available

This is the statement which drew my comment.
The efficiency of a 1/2 WL dipole and a 1 WL loop are so close as
to be almost unmeasurable in the real world.

Almost doesn't count when measuring efficiency and in the real world
many CAN tell the difference
But you can take this even farther. Almost *any* size dipole
or loop will radiate most all of what is fed to it.

Again you are admitting to lower efficiency when you use the word
"most"


A 1/10 WL whip radiates almost all of the power applied to
it, same as a 1/4 WL, 1/2 WL, or whatever you want to try.
This not not conjecture. This is pretty much written in stone
after many years of testing.

Again you use the word "most" which is admitting less efficiency

Why you continue to ignore this simple fact boggles my mind.
So your statement is so far from reality I would be amiss
in my "talking head" duties if I did not comment.
Don't take my word for it. Ask anyone you can think of
that has a clue. They will tell you the same thing.

What it going to spoil your "full size performance from a
dinky radiator" picnic is not the radiator and it's abilities to be
an efficient radiator.
It's going to be actually feeding the power to such a small
radiator and not turning a large amount of RF to heat in the
process. No cheating letting the feed line be the antenna..


I think you are missing the point here. My antenna has a full wave
length of wire
not a fraction there of. So the radiator has the same inductance and
capacitance
that one would expect from a full wave antenna spread out in a
straight line
where the wire surface is exposed to the atmosphere, so there is no
reason
for the energy to circumvent the wire circuit as it must do for a
fractional wavelength.


Look at "small" HF transmitting loops. Do you see any
using 22 gauge wire? I doubt it.
They will be using the fattest or widest strip of material
they can get their hands on.


What you are seeing as representing a loop antenna is a fractional
wave length
Often it comes with a HV variable capacitor for tuning.

The loop that I made was a plastic loop with a full wave length of
wire wound upon it. No high voltage capacitor needed as it coveres
the whole band.
As far as 22 gauge wire being used this is because there is no
mechanical stresses
imposed on it as would be for a stretched out radiator. So the main
consideration
is to supply enough skin depth since the diameter itself
is not a factor in terms of fusing.current

There are other issues involved also in feeding such an
antenna. Never do these small loops equal the performance
of a full size antenna. They radiate enough to maybe let
you operate, and thats about it.


If the scource impedance is one that you can match efficiently
then you have at hand a efficient radiator of a wavelength where
the normal loop you are refering to uses a metal loop as the radiator
which is much shorter than a wavelength of wire wound on a plastic
loop.
The loop is now a small full wave radiator not a small fractional
small wave antenna


This was firmly proven in Quito.Maximum radiation
efficiency requires equilibrium. Period


Again, the change to quad loops at HCJB was to
avoid the sharp points of the dipoles, yagi's, or
whatever they were using. In the high alitudes of
Quito, HV breakdown at the tips was a serious problem.
The change had absolutely nothing to do with antenna
efficiency.

If the impedance is to high on the antenna compared to
discharging through air to the transmitter ground then that
is a very inefficient antenna

Not to mention that the whole idea of a loop being
more efficient than a dipole is totally wrong.

The energy travels easily along the wire circuit without
encountering a high impedance that it is forced to take a circuitous
route thru ground to the transmitter ground. When the energy
is passing thru ground it becomes a loss.

And I don't see how equilibrium has anything to
do with it, whatever you might mean by that silly "E"
word.

If a circuit is not balanced and a fractional wave length long
it is not in equilibrium!. The energy supplied to the radiator
will always encounter a energy wasting impedance in the wire itself if
is not at least a wavelength long, and of the right material
(diamagnetic)
otherwise the energy will seek a route outside the wired circuit which
can only lead to losses. Think of it this way, a fractional wave
length radiator
cannot avoid the energy taking a route thru ground and the ground is a
loss.
Hopefully you now see antennas in a different light. I do urge you to
look up
the tank circuit since it is quite an interesting circuit with its
phase changes
and effective resistances apparently changing without being diverted
from the circuit wire confines. Another place where the books are in
error
is their association with the iron filing magnet experiment at HS
which
forms a magnetic field very different from that formed from aluminum,
copper and other diamagnetic materials. When you pass a time varying
current thru
copper the magnetic field turns at right angles to the radiator axis
and in fact
compliments the electrical field vector ( they are not at right
angles)
Now you can see what lifts or ejects the static particles resting on
the surface
because they are repelled instead of bing magnetically atracted
( Static: nearly devoid of energy and of small mass)
.. So the EH antennas which supposedly combines the EH fields just
didn't
understand that with a radiator the combination of vectors is already
a given!
I think you also are making a mistake that many books make when
referring to
small antennas instead of referring to ELECTRICALLY small antennas

Anything else you are curious about?
BTW, no grabbing of books were needed to form
this response.
Art


Best regards, no offence intended
Art Unwin ......KB9MZ..(uk)
 
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
what size antenna? clu Shortwave 16 October 26th 05 11:25 PM
what size antenna? [email protected] Shortwave 0 October 25th 05 01:55 AM
Recomend Size of Aux Antenna for use with MFJ-1025/6 or ANC-4 Ronald Walters Antenna 2 January 3rd 05 12:00 AM
Question of Antenna Size? Doug Smith W9WI Shortwave 1 August 2nd 04 09:20 AM
Physical size of radiating element? FAZAMY Antenna 3 January 30th 04 03:29 PM


All times are GMT +1. The time now is 02:48 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