Richard Clark wrote in
:

On Sun, 14 Nov 2010 02:25:50 GMT, Owen Duffy wrote:

I meant to elaborate on this a bit more. (Did I hear someone groan?)

If for example, the feedpoint Z of a 0.6 wave vertical over four
quarter wave radials...

I'll bite (or groan as the expectation demands) - why "quarter wave"
radials? A rule of thumb?

It is just what I modelled, so I was declaring the context. The thread
started on 2m, my discussion was in that context, and the usual
application would be elevated radials, I modelled free space.

I used a quarter of the free space wave length. It is not that important
because as you note, matching the feedpoint impedance deals with the
length issue. The reason I didn't specifiy any slope is that they were
horizontal.

Other configurations are possible, but the numbers will vary.

I suggest that as the vertical length approaches a half wave, a set of
shorter radials, and perhaps three might well provide adequate
decoupling... but Z will differ again.

I was not trying to publish a working design, rather to give some info
on the way these things behave.

Owen

....

On Nov 13, 9:11*pm, "Peter" wrote:
Why do you call it a 1/8 wave loading coil? It wouldn't be along the
lines of the flawed "loading coil replaces the missing degrees" concept
would it?

I referred to the 1/8 wave loading coil without really thinking about it. I
was unsure of the loading coil dimensions, so I simple tried a 1/8 wave
length wire formed into a coil. This is for the simple series arrangement
5/8 radiator. This created a load coil that appeared to have a little too
much L so I have removed one turn, seems to load up ok after a little
trimming of the radiator. Keen to hear how too determine the
value/dimensions for the loading coil.

Having said that I'm not sure what so wrong with missing degrees" concept..







A 5/8 monopole's performance is quite senstive to the ground plane
implementation. The behavior of a 5/8 monopole over a perfect ground is
not replicated over real radial systems or car roofs, yet people compare
antennas based on the perfect ground plane environment.

As the length of the radiator is increased beyone a half wave, low angle
gain increaeses until about 0.6 wavelengths when power is shifted into a
developing upper lobe. The optimum length over a perfect ground is
probably just a little less than 5/8, and less still over practical
ground planes.

The other dimension is feedpoint impedance. For a simple series L
matching arrangement, R is a little high and the optimum length is
typically longer than 5/8.

So, for optimum pattern, and low VSWR, a better solution is a tapped base
coil with 0.6 wavelength vertical... but that doesn't play well with the
simplest of mobile antenna bases that provide only one connection to the
screw on antenna.

My current 5/8 wave ground plan project is simply to get something on air,
however I plans to construct an improved version with the tapped coil
approach.

I may be looking in the wrong places, but I have been surprised at how
little information there is on the net regarding 5/8 wave ground plan.

Thanks Owen for the above over view of the 5/8 wave ground plan.

Cheers

Peter VK6YSF

http://members.optushome.com.au/vk6ysf/vk6ysf/main.htm- Hide quoted text -

- Show quoted text -

The way you did it works pretty good. A lot of practical antenna work
is estimate and trim.There is or used to be a site that goes into a
lot of detail on the 5/8ths. I had it in my bookmarks for a long time
but lost it in my last computer crash. Compares 5/8ths with 1/4 wave
radial 5/8 radials horizontal and drooping radials and much more.
Sorry but I cant remember who had the site bet someone here does.



Jimmie

On Nov 13, 10:21*pm, JIMMIE wrote:
On Nov 13, 9:11*pm, "Peter" wrote:



Why do you call it a 1/8 wave loading coil? It wouldn't be along the
lines of the flawed "loading coil replaces the missing degrees" concept
would it?

I referred to the 1/8 wave loading coil without really thinking about it. I
was unsure of the loading coil dimensions, so I simple tried a 1/8 wave
length wire formed into a coil. This is for the simple series arrangement
5/8 radiator. This created a load coil that appeared to have a little too
much L so I have removed one turn, seems to load up ok after a little
trimming of the radiator. Keen to hear how too determine the
value/dimensions for the loading coil.

Having said that I'm not sure what so wrong with missing degrees" concept.

A 5/8 monopole's performance is quite senstive to the ground plane
implementation. The behavior of a 5/8 monopole over a perfect ground is
not replicated over real radial systems or car roofs, yet people compare
antennas based on the perfect ground plane environment.

As the length of the radiator is increased beyone a half wave, low angle
gain increaeses until about 0.6 wavelengths when power is shifted into a
developing upper lobe. The optimum length over a perfect ground is
probably just a little less than 5/8, and less still over practical
ground planes.

The other dimension is feedpoint impedance. For a simple series L
matching arrangement, R is a little high and the optimum length is
typically longer than 5/8.

So, for optimum pattern, and low VSWR, a better solution is a tapped base
coil with 0.6 wavelength vertical... but that doesn't play well with the
simplest of mobile antenna bases that provide only one connection to the
screw on antenna.

My current 5/8 wave ground plan project is simply to get something on air,
however I plans to construct an improved version with the tapped coil
approach.

I may be looking in the wrong places, but I have been surprised at how
little information there is on the net regarding 5/8 wave ground plan.

Thanks Owen for the above over view of the 5/8 wave ground plan.

Cheers

Peter VK6YSF

http://members.optushome.com.au/vk6y.../main.htm-Hide quoted text -

- Show quoted text -

The way you did it works pretty good. A lot of practical antenna work
is estimate and trim.There is or used to be a site that goes into a
lot of detail on the 5/8ths. I had it in my bookmarks for a long time
but lost it in my last computer crash. Compares 5/8ths with 1/4 wave
radial 5/8 radials *horizontal and drooping radials and much more.
Sorry but I cant remember who had the site bet someone here does.

Jimmie

I modeled a few of the usual versions.
http://home.comcast.net/~nm5k/acompari.htm
I had thought I had also modeled a few using resonant
3/4 wave radials, but I guess I had found better modeled
results using the 5/8 radials. But I know the 3/4 wave
radials give a much better pattern than the 1/4 wave
radials, but maybe a tad less gain than 5/8 radials.
But these show why I don't like 1/4 wave radials for
a 5/8 radiator. And Richard may have a point about it
it being an "OCF" antenna. This is why I consider it
perverted. I don't like horizontal OCF antennas either..
Through the years of modeling these, and playing with
them in the real world, I've noticed a few things about
the radials.
I prefer sloping 1/4 wave radials when used with a 1/4
wave radiator. The performance difference between
"straight out" radials is not large, but is about .3 db
or so better with the sloping variety. And you get a
bit better match.
But sloping 1/4 radials with a 5/8 radiator is bad news.
The pattern is even worse than when they are straight out.
So if one were to use 1/4 radials on a 5/8 GP, they should
be straight out for the best results.
But I much prefer using either 3/4 or 5/8 radials with
a 5/8 radiator, and the plots show why.
The pattern is cleaned up, and the high angle lobe
does a vanishing act. You then start to see the
comparative textbook gains at the horizon when comparing
to shorter antennas.
IE: most books will claim a 5/8 antenna to have appx
3 db gain vs the 1/4 wave.
But you won't see that with the short radial version.
The gain is there, but it's not on the horizon where you
want it.
If you look at the azimuth plot for each, note the 1/4 GP
shows about 1.8 dbi, and the 1/2 about 2.1 dbi.
As they should..
But look at the perverted 5/8 version.. A lowly 1.1 dbi
at the horizon, with most of the real gain shooting off
to venus at about 45 degrees.. The antenna is sad, and
needs therapy.. Where is the appx 3 dbi we are
supposed to be seeing?
But if you check the version with sloping 5/8 radials,
we see our expected gain on the horizon. About 3.1
dbi in this plot. That's pretty close to the theoretical
expectations.
But if you make the long radials even steeper to
more closely resemble the collinear, the gain increases
to 4.25 dbi.
You are starting to approach the gain territory of the
dual 5/8 collinear which will show about 5.1 dbi on
the horizon. Assuming good decoupling from the
feed line of course... Decoupling is half the battle,
and if it is ignored, one might as well hang a wet
noodle on the roof, and be done with it.
This explains why I have such a negative view of
1/4 wave radials under a 5/8 whip. It's like using
a band aid to deal with severe chainsaw lacerations.
The blood with still spew, and it will be spewing
up into the air at about 45 degrees from the horizon.
Chortle..
All the speculation about matching seems silly to
me. The matching coil is so simple to apply, it's a
non issue. I've built so many of them, I can tell
you about how many turns to use for any particular
band.. I can usually just guess, and get pretty close.
Maybe tweak a turn or two to get just right..
It's simple, and any matching schemes should
not interfere with the lengths of the elements
if you want the most gain at low angles.
It's like matching a yagi.. I don't alter the element
lengths of a yagi to get a batter match. I use the
appropriate matching scheme, and leave the elements
the length they were designed to be for the gain/fb
the antenna was designed to produce.

On Sun, 14 Nov 2010 05:36:40 -0800 (PST), wrote:

On Nov 13, 10:21*pm, JIMMIE wrote:
On Nov 13, 9:11*pm, "Peter" wrote:



Why do you call it a 1/8 wave loading coil?
{snip}

It's like matching a yagi.. I don't alter the element
lengths of a yagi to get a batter match. I use the
appropriate matching scheme, and leave the elements
the length they were designed to be for the gain/fb
the antenna was designed to produce.






This is a great thread! Cooperative discussions like this are way too
rare!

As a humble student of the Art, I have come to consider each antenna
as belonging to either a Resonant or a Non-Resonant classification.

While there is no "best solution" to most antenna configurations,
understanding the decisions you make and utilizing the available
resources make a big difference in the outcome.

I hope you guys can keep the thread going for a while, you are
answering questions that I have been unable to ask!


John Ferrell W8CCW

On Nov 13, 8:25*pm, Owen Duffy wrote:
If for example, the feedpoint Z of a 0.6 wave vertical over four quarter
wave radials was 150-j500, your tapped coil matching network can be
designed using bulk standard circuit theory to transform 150-j500 to 50
+j0, and nowhere do you use the missing 54° in those calcs.

That's because the lumped-circuit model assumes that all signals
travel instantly at faster than light speeds through the coil. At
instant, faster than light speeds, the coil cannot possibly occupy any
degrees of the antenna. When the real-world speed of light limit is
taken into account by using the distributed network model, the degrees
occupied by the coil falls out as part of those real-world
calculations. The lumped-circuit model is simply flawed for the
purpose of trying to determine the degrees occupied by the coil. I am
finishing up an article on this subject. At 3.5 MHz, the velocity
factor of the 100 turn, 10 inch long coil is 0.04, which makes the
coil occupy 26.4 degrees when used for a 3.5 MHz mobile antenna.

The "Axial Propagation Factor" from the Hamwaves Inductance Calculator
at:

http://hamwaves.com/antennas/inductance.html

can be used to determine the number of degrees occupied by a loading
coil. For the above coil at 3.5 MHz, the axial propagation factor is
1.8118 radians/meter. Multiplying by 1.4554 converts it to degrees/
inch. The coil is 10 inches long so: 1.8118(1.4554)(10) = 26.4 degrees
occupied by that loading coil at 3.5 MHz.

We can model a transmission line as lossless, but none exists in
reality.

We can model a loading coil that occupies zero degrees of the antenna,
but none exists in reality.
--
73, Cecil, w5dxp.com

On Nov 14, 9:36*am, wrote:
On Nov 13, 10:21*pm, JIMMIE wrote:





On Nov 13, 9:11*pm, "Peter" wrote:

Why do you call it a 1/8 wave loading coil? It wouldn't be along the
lines of the flawed "loading coil replaces the missing degrees" concept
would it?

I referred to the 1/8 wave loading coil without really thinking about it. I
was unsure of the loading coil dimensions, so I simple tried a 1/8 wave
length wire formed into a coil. This is for the simple series arrangement
5/8 radiator. This created a load coil that appeared to have a little too
much L so I have removed one turn, seems to load up ok after a little
trimming of the radiator. Keen to hear how too determine the
value/dimensions for the loading coil.

Having said that I'm not sure what so wrong with missing degrees" concept.

A 5/8 monopole's performance is quite senstive to the ground plane
implementation. The behavior of a 5/8 monopole over a perfect ground is
not replicated over real radial systems or car roofs, yet people compare
antennas based on the perfect ground plane environment.

As the length of the radiator is increased beyone a half wave, low angle
gain increaeses until about 0.6 wavelengths when power is shifted into a
developing upper lobe. The optimum length over a perfect ground is
probably just a little less than 5/8, and less still over practical
ground planes.

The other dimension is feedpoint impedance. For a simple series L
matching arrangement, R is a little high and the optimum length is
typically longer than 5/8.

So, for optimum pattern, and low VSWR, a better solution is a tapped base
coil with 0.6 wavelength vertical... but that doesn't play well with the
simplest of mobile antenna bases that provide only one connection to the
screw on antenna.

My current 5/8 wave ground plan project is simply to get something on air,
however I plans to construct an improved version with the tapped coil
approach.

I may be looking in the wrong places, but I have been surprised at how
little information there is on the net regarding 5/8 wave ground plan..

Thanks Owen for the above over view of the 5/8 wave ground plan.

Cheers

Peter VK6YSF

http://members.optushome.com.au/vk6y...htm-Hidequoted text -

- Show quoted text -

The way you did it works pretty good. A lot of practical antenna work
is estimate and trim.There is or used to be a site that goes into a
lot of detail on the 5/8ths. I had it in my bookmarks for a long time
but lost it in my last computer crash. Compares 5/8ths with 1/4 wave
radial 5/8 radials *horizontal and drooping radials and much more.
Sorry but I cant remember who had the site bet someone here does.

Jimmie

I modeled a few of the usual versions.http://home.comcast.net/~nm5k/acompari.htm
I had thought I had also modeled a few using resonant
3/4 wave radials, but I guess I had found better modeled
results using the 5/8 radials. *But I know the 3/4 wave
radials give a much better pattern than the 1/4 wave
radials, but maybe a tad less gain than 5/8 radials.
But these show why I don't like 1/4 wave radials for
a 5/8 radiator. And Richard may have a point about it
it being an "OCF" antenna. This is why I consider it
perverted. I don't like horizontal OCF antennas either.. *
Through the years of modeling these, and playing with
them in the real world, I've noticed a few things about
the radials.
I prefer sloping 1/4 wave radials when used with a 1/4
wave radiator. The performance difference between
"straight out" radials is not large, but is about .3 db
or so better with the sloping variety. And you get a
bit better match.
But sloping 1/4 radials with a 5/8 radiator is bad news.
The pattern is even worse than when they are straight out.
So if one were to use 1/4 radials on a 5/8 GP, they should
be straight out for the best results.
But I much prefer using either 3/4 or 5/8 radials with
a 5/8 radiator, and the plots show why.
The pattern is cleaned up, and the high angle lobe
does a vanishing act. *You then start to see the
comparative textbook gains at the horizon when comparing
to shorter antennas.
IE: most books will claim a 5/8 antenna to have appx
3 db gain vs the 1/4 wave.
But you won't see that with the short radial version.
The gain is there, but it's not on the horizon where you
want it.
If you look at the azimuth plot for each, note the 1/4 GP
shows about 1.8 dbi, and the 1/2 about 2.1 dbi.
As they should..
But look at the perverted 5/8 version.. A lowly 1.1 dbi
at the horizon, with most of the real gain shooting off
to venus at about 45 degrees.. The antenna is sad, and
needs therapy.. * *Where is the appx 3 dbi we are
supposed to be seeing?
But if you check the version with sloping 5/8 radials,
we see our expected gain on the horizon. About 3.1
dbi in this plot. That's pretty close to the theoretical
expectations.
But if you make the long radials even steeper to
more closely resemble the collinear, the gain increases
to 4.25 dbi.
You are starting to approach the gain territory of the
dual 5/8 collinear which will show about 5.1 dbi on
the horizon. Assuming good decoupling from the
feed line of course... Decoupling is half the battle,
and if it is ignored, one might as well hang a wet
noodle on the roof, and be done with it.
This explains why I have such a negative view of
1/4 wave radials under a 5/8 whip. It's like using
a band aid to deal with severe chainsaw lacerations.
The blood with still spew, and it will be spewing
up into the air at about 45 degrees from the horizon.
Chortle..
All the speculation about matching seems silly to
me. The matching coil is so simple to apply, it's a
non issue. I've built so many of them, I can tell
you about how many turns to use for any particular
band.. I can usually just guess, and get pretty close.
Maybe tweak a turn or two to get just right..
It's simple, and any matching schemes should
not interfere with the lengths of the elements
if you want the most gain at low angles.
It's like matching a yagi.. I don't alter the element
lengths of a yagi to get a batter match. I use the
appropriate matching scheme, and leave the elements
the length they were designed to be for the gain/fb
the antenna was designed to produce.- Hide quoted text -

- Show quoted text -

Thanks thats the data I was looking for but I dont believe it is the
same site. More than good enough.

On Sun, 14 Nov 2010 10:08:24 -0500, John Ferrell
wrote:

While there is no "best solution" to most antenna configurations,
understanding the decisions you make and utilizing the available
resources make a big difference in the outcome.

Hi John,

True, this has everything to do with utility.

I hope you guys can keep the thread going for a while, you are
answering questions that I have been unable to ask!

It's easier to keep the thread going (productively) if you could choke
up a question.

If I were to rummage for key points in the hopes of doing what you
ask, I could as easily bore you (everyone).

Fishing for just such an example, and returning to both drooping
radials on a 5/8ths and how that might cause this design to suffer
equally with the worst of J-Pole performances, let's look at the
silhouette of the 5/8ths with drooping radials:

Overall, it gives us a radiator that starts out 5/8ths tall (radials
out at 90 deg), or gets "taller" as those radials droop. In the
extreme (radials fallen to 0 deg), we now have a 7/8ths tall radiator
(my aforementioned OCF vertical dipole). Neglecting problems of
feedpoint Z, this radiator lobe pattern could be pushed beyond the two
towards developing four lobes. Without checking this in EZNEC (left
for the student to perform), this could result in transforming an
already higher gain antenna into becoming a cloud warmer.

This (the additional, higher lobes) is often the fate of the J-Pole
when the line that feeds it becomes part of the radiator. We get
glowing reports of how well J-Poles have been built and matched, and
sometimes grief over how deaf they are (How could this be?).

73's
Richard Clark, KB7QHC

"JIMMIE" wrote in message
...
On Nov 14, 9:36 am, wrote:
On Nov 13, 10:21 pm, JIMMIE wrote:

Thanks thats the data I was looking for but I dont believe it is the
same site. More than good enough.

That is interesting. Just when I thought I was getting a handle on things
its back to the old drawing board!

Keen to hear comments on the plots presented per the link.

http://home.comcast.net/~nm5k/acompari.htm

--
Peter VK6YSF

http://members.optushome.com.au/vk6ysf/vk6ysf/main.htm

"Ralph Mowery" wrote in message
m...

"David" nospam@nospam wrote in message
...

I would not say any of the simple veticals are better. While I have not
tried them from fixed locations, expirimenting with several differant
mobile antennas over the years it seems that one type is not really that
much beter than another.

Depending on the direction and height of the repeaters almost any antenna
can be better going into one repeater and worse going to another.
Several of us got together and put several antennas (one at a time) on the
same mount of a car. Depending on the particular repeater, there was not
one overall winner. The car also had a 40 meter loaded whip that we tried
and it was actually better into some of the repeaters.

About the only antenna overall not suited was a colinear about 6 feet
long. It worked well enough while parked, but at highway speeds it whipped
around so much the mobile flutter made it almost unusable.

My experience with mobile vertical whips has been similar, I guess at least
in my case the location of the antenna was always a compromise and car
body's are not designed to be ideal ground plans.
I did get quite good at knowing where some of the good lobes were and
positioning the car accordingly.


--
Peter VK6YSF

http://members.optushome.com.au/vk6ysf/vk6ysf/main.htm

On Nov 14, 9:32*am, Cecil Moore wrote:
On Nov 13, 9:35*pm, Richard Clark wrote:

This
equivalence "replacement" is forced further into unresolved exactness
if we move the same coil up into the radiator (without changing the
radiator's length).

From a conceptual standpoint, there is no "unresolved exactness".
Considering a base-loaded antenna vs a center-loaded antenna:

I am writing an article that conceptually explains it all.

The first part of the article has been published:

http://www.eham.net/articles/24940
--
73, Cecil, w5dxp.com