Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #51   Report Post  
Old April 5th 14, 07:54 AM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Jul 2006
Posts: 757
Default Radials

On Friday, April 4, 2014 9:16:01 PM UTC-5, Fred McKenzie wrote:


3. Ground is relatively flat. Drooping radials to approximate a sleeve

dipole is stretching the definition of a ground plane!


The best modeled version of the 5/8 with 5/8 radials scheme, I
consider more of a dual 5/8 collinear than a 5/8 ground plane.
You don't get the full 5.1 dbi free space gain of the straight
collinear, but you get fairly close.
But.. I don't really care about the name.. Just as long as they work.



  #54   Report Post  
Old April 5th 14, 02:40 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Jul 2006
Posts: 317
Default Radials

In article ,
Ian Jackson wrote:

I understand that my 2m 5/8 mobile antenna (on a magmount) is
essentially electrically a 6/8 (ie a 3/4 wave - hence a good match). The
actual whip is around 5/8, and the other 1/8 is the 3-turn spring steel
'loading' coil at the bottom end.

Again my understanding is that a 5/8 gives the maximum broadside gain (a
tiddly bit more oomph than a 1/2 wave), and if you make the antenna
longer, the predominant broadside lobe collapses, and most of radiation
moves to the higher angle lobe.


I read somewhere that the maximum gain toward the horizon, was obtained
with a 0.58 wavelength vertical element rather than 5/8 (0.625).

The advantage of a 5/8 antenna with a flat ground plane, is that its
impedance is capacitive with a 50 Ohm resistive component. A small
inductor (loading coil) cancels the capacitance.

Fred
K4DII
  #55   Report Post  
Old April 5th 14, 05:33 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Jun 2006
Posts: 1,898
Default Radials

Ian Jackson wrote:
In message ,
writes
Fred McKenzie wrote:
In article ,
Wimpie wrote:

I know the "classical" definition, but we live in 2014, and when the
scope of some definitions changed over the last 20..30 years, it is
good to know how they changed to avoid misunderstandings. Visit some
antenna manufacturer's websites and see what changed over the years
(that doesn't mean that I agree with them).

1. There are industry standards, but some antenna manufacturers use
numbers and definitions to make their products more attractive. That
has not changed over the last many years.

2. The feature that defines a ground plane antenna is the ground plane,
not the vertical element.

3. Ground is relatively flat. Drooping radials to approximate a sleeve
dipole is stretching the definition of a ground plane!


The Radials of a ground plane antenna work entirely differently than the
sleeve in a sleeve dipole, drooping or otherwise.

I would question 'entirely'. In my simplistic ignorance, I would have
thought that as you increase the angle of dangle, one kind of morphs
into the other.


Does bread dough "morph" into bread when you bake it or does it become
something different?

A sleeve dipole is a dipole with a skinny and fat element. The fat element
is also a common mode choke.

A ground plane antenna is a monopole mounted over ground. The common usage
is that a GP uses an artificial ground consisting of radials.


--
Jim Pennino


  #56   Report Post  
Old April 6th 14, 12:43 AM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Jul 2006
Posts: 757
Default Radials

On Saturday, April 5, 2014 8:40:31 AM UTC-5, Fred McKenzie wrote:
In article ,

Ian Jackson wrote:



I understand that my 2m 5/8 mobile antenna (on a magmount) is


essentially electrically a 6/8 (ie a 3/4 wave - hence a good match). The


actual whip is around 5/8, and the other 1/8 is the 3-turn spring steel


'loading' coil at the bottom end.




Again my understanding is that a 5/8 gives the maximum broadside gain (a


tiddly bit more oomph than a 1/2 wave), and if you make the antenna


longer, the predominant broadside lobe collapses, and most of radiation


moves to the higher angle lobe.




I read somewhere that the maximum gain toward the horizon, was obtained

with a 0.58 wavelength vertical element rather than 5/8 (0.625).


I'm not sure if that gives the maximum gain vs a .64 wave, but
it gives the cleanest pattern, with the least radiation skewing
upwards. So most of the AM broadcasters that use 5/8 radiators
prefer them on the shorter side from what I've read.



The advantage of a 5/8 antenna with a flat ground plane, is that its

impedance is capacitive with a 50 Ohm resistive component. A small

inductor (loading coil) cancels the capacitance.


I didn't see much if any changes in the loading coil no matter
what I did for radials. IE: I used the same coil for all of them,
and never had to change it when I added longer radials, etc.
I did not use a grounded coil. I just ran it in series. That way
I was able to use the antenna on 30m as a 1/4 wave.

And the same when I had the full size 40m 1/4 GP. I also used
it on 17m as a 5/8 GP, and used a 24v relay to bypass the coil
for 40m. That way I could switch from the shack.
Kinda hard to reach when the base of the GP is 36 ft up.. lol..
I used a full size 32 ft aluminum radiator, with the tip made of
car whip to reduce weight and wind load. The lower tubing was
double walled to be stronger. Almost 70 ft to the top of that thing.
It kicked butt on 40 and 17 both. Good on 40m DX late at night,
and I was running a KW+ on top of that, just to make sure I browned
the food across the ponds. I also had a 40m horizontal dipole at 36 ft,
and to DX, the vertical was usually about 2 S units better to the
U.S. coasts, and often 4 S units better across the pond. The longer
the path, the better the vertical did. Also had a good ground wave,
which was often noticed in the daytime.


  #57   Report Post  
Old April 7th 14, 02:54 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Mar 2008
Posts: 329
Default Radials

El 05-04-14 9:46, Ian Jackson escribió:
In message ,
writes
On Friday, April 4, 2014 9:16:01 PM UTC-5, Fred McKenzie wrote:


3. Ground is relatively flat. Drooping radials to approximate a sleeve

dipole is stretching the definition of a ground plane!


The best modeled version of the 5/8 with 5/8 radials scheme, I
consider more of a dual 5/8 collinear than a 5/8 ground plane.
You don't get the full 5.1 dbi free space gain of the straight
collinear, but you get fairly close.
But.. I don't really care about the name.. Just as long as they work.


I understand that my 2m 5/8 mobile antenna (on a magmount) is
essentially electrically a 6/8 (ie a 3/4 wave - hence a good match).
The actual whip is around 5/8, and the other 1/8 is the 3-turn spring
steel 'loading' coil at the bottom end.

Again my understanding is that a 5/8 gives the maximum broadside gain
(a tiddly bit more oomph than a 1/2 wave), and if you make the antenna
longer, the predominant broadside lobe collapses, and most of
radiation moves to the higher angle lobe.








The "theoretical" more gain for a 5/8 lambda radiator over a half wave
dipole is only valid when towards the direction of reception, you have
a fully constructive image antenna in the ground.

To fullfill this:

1# The elevation angle needs to be well above the (pseudo) brewster
angle, to make sure that the ground reflection is strong and more or
less in phase.

2# The ground plane needs to cover at least about the first Fresnel
zone as seen from the negative image antenna towards the reciever.

When you look to real far field patterns of 5/8 lambda antennas as
used in AM broadcast over land, the pattern only matches the
theoretical pattern for elevation angle say above 5..10 degr
(depending on soil type). For lower elevation, you are below the
brewster angle and then the effect of the negative image becomes more
destructive with decreasing elevation, hence decreasing gain.

For HF, VHF and higher, the ground plane will never meet 2#. To meet
this, the ground plane (metallic plane) needs to extend from the
transmitter towards the receiver. You can't count mother earth as
constructive ground as that serves as a destructive image as the
elevation angle is well below the (pseudo) Brewster angle.

For mobile LOS use, the advantage of the 5/8 lambda is not in the
gain, but in its heigth, as propagation in a mobile path is roughly
spoken proportional to h^2. So when the current center goes from 2.5 m
(quarter wave on a car, 2 m band) to 3.3 m (5/8 lambda on same car),
you win 2.4 dB.

For a base station where the ground provision (for example 4 quarter
wave radials) is already many lambda above mother earth, the
additional gain due to the increased length is mininmal.



--
Wim
PA3DJS
Please remove abc first in case of PM
  #58   Report Post  
Old April 8th 14, 12:24 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: May 2011
Posts: 550
Default Radials

On 4/7/2014 8:54 AM, Wimpie wrote:
El 05-04-14 9:46, Ian Jackson escribió:
In message ,
writes
On Friday, April 4, 2014 9:16:01 PM UTC-5, Fred McKenzie wrote:


3. Ground is relatively flat. Drooping radials to approximate a sleeve

dipole is stretching the definition of a ground plane!


The best modeled version of the 5/8 with 5/8 radials scheme, I
consider more of a dual 5/8 collinear than a 5/8 ground plane.
You don't get the full 5.1 dbi free space gain of the straight
collinear, but you get fairly close.
But.. I don't really care about the name.. Just as long as they work.


I understand that my 2m 5/8 mobile antenna (on a magmount) is
essentially electrically a 6/8 (ie a 3/4 wave - hence a good match).
The actual whip is around 5/8, and the other 1/8 is the 3-turn spring
steel 'loading' coil at the bottom end.

Again my understanding is that a 5/8 gives the maximum broadside gain
(a tiddly bit more oomph than a 1/2 wave), and if you make the antenna
longer, the predominant broadside lobe collapses, and most of
radiation moves to the higher angle lobe.








The "theoretical" more gain for a 5/8 lambda radiator over a half wave
dipole is only valid when towards the direction of reception, you have a
fully constructive image antenna in the ground.

To fullfill this:

1# The elevation angle needs to be well above the (pseudo) brewster
angle, to make sure that the ground reflection is strong and more or
less in phase.

2# The ground plane needs to cover at least about the first Fresnel zone
as seen from the negative image antenna towards the reciever.

When you look to real far field patterns of 5/8 lambda antennas as used
in AM broadcast over land, the pattern only matches the theoretical
pattern for elevation angle say above 5..10 degr (depending on soil
type). For lower elevation, you are below the brewster angle and then
the effect of the negative image becomes more destructive with
decreasing elevation, hence decreasing gain.

For HF, VHF and higher, the ground plane will never meet 2#. To meet
this, the ground plane (metallic plane) needs to extend from the
transmitter towards the receiver. You can't count mother earth as
constructive ground as that serves as a destructive image as the
elevation angle is well below the (pseudo) Brewster angle.

For mobile LOS use, the advantage of the 5/8 lambda is not in the gain,
but in its heigth, as propagation in a mobile path is roughly spoken
proportional to h^2. So when the current center goes from 2.5 m (quarter
wave on a car, 2 m band) to 3.3 m (5/8 lambda on same car), you win 2.4 dB.

For a base station where the ground provision (for example 4 quarter
wave radials) is already many lambda above mother earth, the additional
gain due to the increased length is mininmal.



Excellent information, Wim. Thanks.

John, KD5YI

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
radials for Cushcraft AV5 Daniel Ferrato - IK2SGL Antenna 3 August 23rd 19 01:33 AM
radials Jeff Arrowsmith Antenna 9 April 16th 13 11:20 AM
Radials Rick Antenna 5 February 28th 07 07:13 AM
Radials hasan schiers Antenna 0 March 22nd 06 11:42 PM
Radials for 6-BTV rhymer Antenna 5 May 31st 04 01:55 AM


All times are GMT +1. The time now is 02:23 PM.

Powered by vBulletin® Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 RadioBanter.
The comments are property of their posters.
 

About Us

"It's about Radio"

 

Copyright © 2017