"Peter" wrote in
. au:

....
construct as there is a bit of mucking about with 1/8wave loading coil
on the 5/8 antenna.

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?

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.

Owen

On Nov 9, 3:02*pm, Owen Duffy 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?

Of course, the loading coil doesn't replace all of the missing
degrees, but it does replace some of the missing degrees. The
following inductance calculator will give the Z0 and axial propagation
factor of a coil from which the VF of the coil can be calculated. When
one knows the Z0 and VF of the coil, it can simply be treated as a
transmission line.

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

It is obvious that the loading coil at the bottom of a 5/8WL antenna
somehow causes the antenna to be electrically 3/4WL (270 degrees) long
because that's the only way the reflected wave can arrive back at the
feedpoint in phase with the forward wave in order to give a resistive
feedpoint impedance. So we need to answer the question of exactly
where those delays and phase shifts occur. Here's a conceptual model
of the 5/8WL base-loaded antenna. (The 50 ohm tapped point on the coil
has been ignored to simplify the problem.)

FP-//////////-----------5/8WL-------------------

(1) The coil occupies a certain number of degrees of the antenna. (2)
Since the Z0 of the coil and the Z0 of the whip are different, there
is a phase shift at the junction of the coil and the whip that can be
easily calculated. (3) The 5/8WL whip obviously occupies 225 degrees
of the antenna. All we have to do is figure out what the phase shift
is at the coil/whip junction and how many degrees the coil occupies.

degrees of coil = 270 - 225 - coil/whip phase shift

There's no magical faster-than-light propagation through the coil as
predicted by the lumped-circuit model. Coils are known to cause a
delay and the Hamwaves inductance calculator provides us an easy way
of calculating that delay through the loading coil. I can provide an
example if necessary.
--
73, Cecil, w5dxp.com

On Nov 9, 6:39*pm, Cecil Moore wrote:
... the Hamwaves inductance calculator provides us an easy way
of calculating that delay through the loading coil.

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

Assume a 10" long, 100 turn coil with a diameter of 2" wound with #18
wire. In metric, that's 254 mm long, 50.8 mm diameter, and 1.024 mm
wire. At 4 MHz, the above calculator indicates that the axial
propagation factor is 2.122 rad/m which we can convert to degrees/inch
by multiplying by 1.4554 which yields 3.088 degrees per inch. The coil
is 10 inches long so the number of degrees occupied by the coil at 4
MHz is 30.9 degrees.

If this coil is used as a base loading coil in a 4 MHz mobile antenna,
it occupies ~30.9 degrees of the antenna. A 7 foot whip occupies ~10.2
degrees at 4 MHz. The antenna, at resonance, is known to be 90 degrees
long. So the phase shift at the coil to whip junction has to be ~48.9
degrees assuming resonance at 4 MHz.

For an electrical 1/4WL base-loaded antenna, e.g. an HF mobile
antenna, there exist three phase shifts that add up to 90 degrees. The
phase shift through the coil plus the coil to whip junction phase
shift plus the phase shift through the whip have to add up to 90
degrees. For a center-loaded antenna, there are four phase shifts that
must add up to 90 degrees. The phase shift at the base to bottom of
loading coil junction is negative. That's why we need more inductance,
i.e. more phase shift, in the center-loading coil than we do in the
base loading coil.

If we are dealing with a 5/8WL (225 deg) antenna, the phase shift
through the base coil plus the phase shift at the coil to whip
junction must add up to 45 degrees such that 225 deg + 45 deg = 270
deg = 6/8WL.
--
73, Cecil, w5dxp.com

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

On Nov 13, 7:11*pm, "Peter" wrote:
Having said that I'm not sure what so wrong with missing degrees" concept..

:-) Because there are two sides of the argument each at the two
extremes. The technical truth is that the coil does replace a certain
number of degrees of the missing part of the antenna but not all of
the missing degrees. I am preparing a technical article that explains
the details. Please stand by.
--
73, Cecil, w5dxp.com

On Sun, 14 Nov 2010 09:11:22 +0800, "Peter" wrote:

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

Hi Peter,

Drives some up the wall. Your terming it as a concept is perfect, but
it will still be argued for being a corrupt teaching of a literal
equivalence.

73's
Richard Clark, KB7QHC

"Peter" wrote in
:

....
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.


Hi Peter,

One theoretical method is to model the antenna, and find the feedpoint
impedance. The R component decreases as length increases from a half wave
to three quarter wave, and X increases towards zero.

Best pattern is closer to a half wave, but R is very high. At 0.7
wavelengths, R is low enough for an acceptable match by using a series
inductor, and reactance will be a few hundred ohms give or take depending
on length.

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

For one thing, if a certain inductance is required, the quantity of wire
needed depends on several underlying coil parameters.


....

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.

That lets you shorten it for a bit more gain, and a good match.

If you cut the vertical for 0.6 wavelengths, you should think of starting
with an inductor with reactance towards 1000 ohms.


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.

Probably displaced by OTS 4 band verticals.

Have fun.

Owen

Owen Duffy wrote in
:

"Peter" wrote in
:
....

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.

That lets you shorten it for a bit more gain, and a good match.

If you cut the vertical for 0.6 wavelengths, you should think of
starting with an inductor with reactance towards 1000 ohms.


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 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 might
suggest that the "missing degrees" are some kind of explanatory crutch
(or ham speak) that is not directly related to solving the problem.

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.