El 03-04-14 20:54, escribió:
wrote:

snip

My results (IE3D, now Mentor Graphics Hyperlynx):
Quarter wave radiator over 4 quarter wave radials, no sloping:
impedance at resonance 23 Ohms, Gain at zero elevation: 1.52 dBi

0.625 wave radiator over 4 quarter wave radials, no sloping:
Gain at zero elevation: 1.52 dBi, 2.29 dBi at 20 degr elevation.

And an impedance in the hundreds of Ohms.

From my memory it was closer to 50 Ohms, but for the gain figures
this isn't important.


0.5 wave radiator over 4 quarter wave radials, no sloping:
Gain at zero elevation: 2.05 dBi.

And an impedance of about 1,000 Ohms.

Depends strongly on thickness/lambda ratio, therefore I didnt mention
the value, and it isn't important for the gain.

Quarter wave radiator over 4 quarter wave radials, 45 degrees sloping:
Impedance at resonance 54 Ohms, gain at zero elevation: 1.97 dBi

Quarter wave radiator over 4 quarter wave radials, 85 degrees sloping:
Impedance at resonance 74 Ohms, gain at zero elevation: 2.14 dBi

All in free space, without a mast.

Again, in free space the maximum is ALWAYS at zero elevation.

Except for the 5/8 lambda, as I mentioned.


Adding a mast, especially for the sloping case can give large
deviation depending on the CM impedance as seen from the floating
ground. I did simulations and current measurements for my own mast,
but the results cannot be applied to other configurations.

As I stated before, the difference between the configurations is
hardly measurable. Nice to see that the over-rated 5/8 lambda antenna
doens't perform better then the quarter wave antenna (at low elevation
angle).

I wouldn't call an impedance range of 20 Ohms to 1000 Ohms "hardly
measurable". In real life you have to feed the thing.

We were discussing gain....


Though the design is more demanding, I prefer the half wave option as
you can use less, sloping, shorter radials without running into common
mode mast current problems.

And requires some sort of feed arrangement to transform 1,000 Ohms into
50 Ohms.

In my opinion, dealing with the added complexity of impedance matching,
which is almost always narrow banded, is not worth a dB or two of gain.

I think I will stick with 5% longer radials at 45 deg and some ferrite at
the feed point.


What someone will use, depends on many factors (not only electrical
ones).

I have some experience with HV, and I know how to design these
circuits without loosing useful bandwidth, so I prefer the half wave.
I like racing and wood pigeons, but not on my antennas! In residential
areas over here, generally people don't like to see lots of aluminum
in the air.

So for my situation it is not the less then 0.5 dB addditional gain
over a classic 4 radial GP, but just the common mode issue together
with visible apearance (I don't want 4 radials). Note that we have
maximum 400WPEP in PA-land, that also makes it easier.



--
Wim
PA3DJS
Please remove abc first in case of PM

On Thursday, April 3, 2014 2:28:40 PM UTC-5, Wimpie wrote:


Again, in free space the maximum is ALWAYS at zero elevation.



Except for the 5/8 lambda, as I mentioned.

That's only because you used 1/4 WL radials, which is a very
perverted design. Try it with 3/4 WL radials. That will give you
close to your textbook gain.
And for an even better pattern use sloping 5/8 WL radials, which
will start approaching the gain of a dual 5/8 WL collinear.

I've compared 1/4 wave GP's, 1/2 wave's with decoupling, and
5/8 GP's with 3/4 and 5/8 radials on 10m to distant local
stations, which is a good test of low angle performance.

The 5/8 was always the best antenna in the real world using
low angle space wave paths 30-40 miles across town.
And the 1/2 wave was better than the 1/4 GP.
The only reason the poor 5/8's get a bad rap is because people
insist on using 1/4 WL radials under them. That's a disaster,
particularly if used on VHF/UHF where the pattern is really
critical.

El 03-04-14 23:29, escribió:
On Thursday, April 3, 2014 2:28:40 PM UTC-5, Wimpie wrote:


Again, in free space the maximum is ALWAYS at zero elevation.



Except for the 5/8 lambda, as I mentioned.

That's only because you used 1/4 WL radials, which is a very
perverted design. Try it with 3/4 WL radials. That will give you
close to your textbook gain.

For zero elevation (relevant for line of sight comms in VHF and up),
the gain will virtually not improve when using horizontal 3/4 WL
radials. The horizontal radials don't contribute to the vertically
polarized wave.

And for an even better pattern use sloping 5/8 WL radials, which
will start approaching the gain of a dual 5/8 WL collinear.

Agree, that really helps! You have to take care of mast/feeder
radiation that may distort the pattern (hence gain) significantly.


I've compared 1/4 wave GP's, 1/2 wave's with decoupling, and
5/8 GP's with 3/4 and 5/8 radials on 10m to distant local
stations, which is a good test of low angle performance.

The 5/8 was always the best antenna in the real world using
low angle space wave paths 30-40 miles across town.

Probably this was because of the added heigth for the 5/8 lambda
radiator over a half or quarter wave, or you had (somewhat) sloping
5/8 WL radials.


And the 1/2 wave was better than the 1/4 GP.
The only reason the poor 5/8's get a bad rap is because people
insist on using 1/4 WL radials under them. That's a disaster,
particularly if used on VHF/UHF where the pattern is really
critical.

Agree, this was the reason I mentioned "over-rated" for the
commercially sold 5/8 lambda antennas, they all have 1/4 lambda
radials. If you make them 3/4 WL, the antenna will be significantly
more expensive and the visual appearance becomes massive (and many
people don't like that).

I had long discussions about this, as many people still believe that
there is a big difference between the 5/8 lambda with 1/4 radials and
the "GPA 27" (the half wave end-fed with no or short radials).


--
Wim
PA3DJS
Please remove abc first in case of PM

On Friday, April 4, 2014 8:39:52 AM UTC-5, Wimpie wrote:



For zero elevation (relevant for line of sight comms in VHF and up),

the gain will virtually not improve when using horizontal 3/4 WL

radials. The horizontal radials don't contribute to the vertically

polarized wave.

Horizontal no.. Try them sloping. As far as I know, the only
case where horizontal radials are preferred would be with the
5/8 radiator with 1/4 radials. In that case, they are better
straight out than sloping. But if I remember right, all other
cases will be better with sloping radials.




And for an even better pattern use sloping 5/8 WL radials, which

will start approaching the gain of a dual 5/8 WL collinear.



Agree, that really helps! You have to take care of mast/feeder

radiation that may distort the pattern (hence gain) significantly.

Sure. But one should do that with any elevated vertical for the
best performance.





I've compared 1/4 wave GP's, 1/2 wave's with decoupling, and

5/8 GP's with 3/4 and 5/8 radials on 10m to distant local

stations, which is a good test of low angle performance.



The 5/8 was always the best antenna in the real world using

low angle space wave paths 30-40 miles across town.



Probably this was because of the added heigth for the 5/8 lambda

radiator over a half or quarter wave, or you had (somewhat) sloping

5/8 WL radials.

They were sloping. But... I remember that I started out with
a 5/8 with 1/4 radials. It was also better than the 1/2 wave even
with the theoretical problems.. It could have been due to the higher
radiator, but not sure.. I'm not sure if an extra 5 feet in height
would make that big a difference on a 30 mile local path when the
base was a fixed 36 feet high in all cases. Could be, with the current
distribution of the usual 5/8 wave element.

El 04-04-14 18:25, escribió:
On Friday, April 4, 2014 8:39:52 AM UTC-5, Wimpie wrote:



For zero elevation (relevant for line of sight comms in VHF and up),

the gain will virtually not improve when using horizontal 3/4 WL

radials. The horizontal radials don't contribute to the vertically

polarized wave.

Horizontal no.. Try them sloping. As far as I know, the only
case where horizontal radials are preferred would be with the
5/8 radiator with 1/4 radials. In that case, they are better
straight out than sloping. But if I remember right, all other
cases will be better with sloping radials.

You are right. The feed current for a 5/8 has almost opposite phase
over the current in the upper half of the 5/8 radiator. So when you
slope the quarter wave radials, the radiator current has almost
opposite phase w.r.t. the phase of the radiator, so the field of the
radials is out of phase with the field from the radiator.

When you make the radials also 5/8 lambda long, you have both phase
reversal in the radiator and the radials, and then the radial current
is almost in phase with the radiator current (as in a 1.25 lambda
center fed dipole). You have more gain (as you already mentioned), but
the radial network is no longer a good floating ground, so you need
some CM suppression in the feed line or mast.

With tall masts (especially without metal guys), you can have really
weird results.





And for an even better pattern use sloping 5/8 WL radials, which

will start approaching the gain of a dual 5/8 WL collinear.



Agree, that really helps! You have to take care of mast/feeder

radiation that may distort the pattern (hence gain) significantly.

Sure. But one should do that with any elevated vertical for the
best performance.





I've compared 1/4 wave GP's, 1/2 wave's with decoupling, and

5/8 GP's with 3/4 and 5/8 radials on 10m to distant local

stations, which is a good test of low angle performance.



The 5/8 was always the best antenna in the real world using

low angle space wave paths 30-40 miles across town.



Probably this was because of the added heigth for the 5/8 lambda

radiator over a half or quarter wave, or you had (somewhat) sloping

5/8 WL radials.

They were sloping. But... I remember that I started out with
a 5/8 with 1/4 radials. It was also better than the 1/2 wave even
with the theoretical problems.. It could have been due to the higher
radiator, but not sure.. I'm not sure if an extra 5 feet in height
would make that big a difference on a 30 mile local path when the
base was a fixed 36 feet high in all cases. Could be, with the current
distribution of the usual 5/8 wave element.

You are right, 5 feet over 36 feet doesn't make a big difference (I
think 1 dB), provided that the 36 feet is in the clear. Maybe you had
possitive contribution from mast current (I am in guessing mode now...).

Other thing with the half wave end-fed can be absorption of the
plastic insulation. To make UV-resistant black they frequently use
carbon black. When the concentration is too high the dissipation
factor of the plastic increases signficantly. Recently I had really
weird results with a half wave monopole design. Everything went wrong.
It was the black UV-stabilized HMPE plastic containing around 2.5%
carbon black. When changing to green HMPE everything was according to
my calculations.


--
Wim
PA3DJS
Please remove abc first in case of PM

On Friday, April 4, 2014 11:58:29 AM UTC-5, Wimpie wrote:

Other thing with the half wave end-fed can be absorption of the

plastic insulation. To make UV-resistant black they frequently use

carbon black. When the concentration is too high the dissipation

factor of the plastic increases signficantly. Recently I had really

weird results with a half wave monopole design. Everything went wrong.

It was the black UV-stabilized HMPE plastic containing around 2.5%

carbon black. When changing to green HMPE everything was according to

my calculations.

All my 1/2 waves have been made from aluminum tubing, and fed with
the gamma loop type matching scheme.
They worked very well, and my final version had a decoupling section
with a lower set of radials.
But all the variations of 5/8 antennas did even better on 10m local paths.

Wimpie wrote:
El 03-04-14 23:29, escribió:
On Thursday, April 3, 2014 2:28:40 PM UTC-5, Wimpie wrote:


Again, in free space the maximum is ALWAYS at zero elevation.



Except for the 5/8 lambda, as I mentioned.

That's only because you used 1/4 WL radials, which is a very
perverted design. Try it with 3/4 WL radials. That will give you
close to your textbook gain.

For zero elevation (relevant for line of sight comms in VHF and up),
the gain will virtually not improve when using horizontal 3/4 WL
radials. The horizontal radials don't contribute to the vertically
polarized wave.

And for an even better pattern use sloping 5/8 WL radials, which
will start approaching the gain of a dual 5/8 WL collinear.

A 5/8 system mounted at 13 feet (top of an average house) will have a
squarish pattern with a maximum of 4.4 dBi and a minimum of 2.2 dBi.

A 1/4 system at the same height has a circular pattern of 4.9 dBi.

In both cases the major elevation lobe is at 20 degrees.

Free space patterns can look wonderfull, but unless you live on the ISS
your antenna is going to be mounted over ground.



--
Jim Pennino

On Friday, April 4, 2014 12:26:30 PM UTC-5, wrote:


A 5/8 system mounted at 13 feet (top of an average house) will have a

squarish pattern with a maximum of 4.4 dBi and a minimum of 2.2 dBi.



A 1/4 system at the same height has a circular pattern of 4.9 dBi.



In both cases the major elevation lobe is at 20 degrees.



Free space patterns can look wonderfull, but unless you live on the ISS

your antenna is going to be mounted over ground.


True, but all mine have been at 36-40 feet up, so the numbers
change a bit.
When I modeled them all, I used a height of 40 ft, and "avg" ground
if I remember right.

At 40 ft, the 1/4 GP with sloping radials gave a max 3.003 dbi at 9 degrees.

The 1/2 wave gave a max 3.831 dbi at 8 degrees.

The 5/8 with straight 1/4 radials, 4.293 dbi at 39 degrees.. Not good.

The 5/8 with 45 degree sloping 5/8 radials, 4.941 dbi at 8 degrees.

The same with even steeper sloping radials, 5.334 dbi at 9 degrees.

wrote:
On Friday, April 4, 2014 12:26:30 PM UTC-5, wrote:


A 5/8 system mounted at 13 feet (top of an average house) will have a

squarish pattern with a maximum of 4.4 dBi and a minimum of 2.2 dBi.



A 1/4 system at the same height has a circular pattern of 4.9 dBi.



In both cases the major elevation lobe is at 20 degrees.



Free space patterns can look wonderfull, but unless you live on the ISS

your antenna is going to be mounted over ground.


True, but all mine have been at 36-40 feet up, so the numbers
change a bit.
When I modeled them all, I used a height of 40 ft, and "avg" ground
if I remember right.

At 40 ft, the 1/4 GP with sloping radials gave a max 3.003 dbi at 9 degrees.

The 1/2 wave gave a max 3.831 dbi at 8 degrees.

The 5/8 with straight 1/4 radials, 4.293 dbi at 39 degrees.. Not good.

The 5/8 with 45 degree sloping 5/8 radials, 4.941 dbi at 8 degrees.

The same with even steeper sloping radials, 5.334 dbi at 9 degrees.

Yes, height makes a HUGE difference which is why when quoting numbers it
is important to state the height.



--
Jim Pennino

Wimpie wrote:
El 03-04-14 20:54, escribió:
wrote:

snip

My results (IE3D, now Mentor Graphics Hyperlynx):
Quarter wave radiator over 4 quarter wave radials, no sloping:
impedance at resonance 23 Ohms, Gain at zero elevation: 1.52 dBi

0.625 wave radiator over 4 quarter wave radials, no sloping:
Gain at zero elevation: 1.52 dBi, 2.29 dBi at 20 degr elevation.

And an impedance in the hundreds of Ohms.

From my memory it was closer to 50 Ohms, but for the gain figures
this isn't important.

But it is if you want to attach the antenna to a real radio.

0.5 wave radiator over 4 quarter wave radials, no sloping:
Gain at zero elevation: 2.05 dBi.

And an impedance of about 1,000 Ohms.

Depends strongly on thickness/lambda ratio, therefore I didnt mention
the value, and it isn't important for the gain.

But again, it is if you want to attach the antenna to a real radio.

Quarter wave radiator over 4 quarter wave radials, 45 degrees sloping:
Impedance at resonance 54 Ohms, gain at zero elevation: 1.97 dBi

Quarter wave radiator over 4 quarter wave radials, 85 degrees sloping:
Impedance at resonance 74 Ohms, gain at zero elevation: 2.14 dBi

All in free space, without a mast.

Again, in free space the maximum is ALWAYS at zero elevation.

Except for the 5/8 lambda, as I mentioned.

Yep, but it isn't a GP antenna which by definition has a radiator about
1/4 lambda.

Adding a mast, especially for the sloping case can give large
deviation depending on the CM impedance as seen from the floating
ground. I did simulations and current measurements for my own mast,
but the results cannot be applied to other configurations.

As I stated before, the difference between the configurations is
hardly measurable. Nice to see that the over-rated 5/8 lambda antenna
doens't perform better then the quarter wave antenna (at low elevation
angle).

I wouldn't call an impedance range of 20 Ohms to 1000 Ohms "hardly
measurable". In real life you have to feed the thing.

We were discussing gain....

You may be discussing gain but I am discussing antenna systems which have
gain, bandwidth and impedance and to be usefull have to be practical to
build.


Though the design is more demanding, I prefer the half wave option as
you can use less, sloping, shorter radials without running into common
mode mast current problems.

And requires some sort of feed arrangement to transform 1,000 Ohms into
50 Ohms.

In my opinion, dealing with the added complexity of impedance matching,
which is almost always narrow banded, is not worth a dB or two of gain.

I think I will stick with 5% longer radials at 45 deg and some ferrite at
the feed point.


What someone will use, depends on many factors (not only electrical
ones).

I have some experience with HV, and I know how to design these
circuits without loosing useful bandwidth, so I prefer the half wave.
I like racing and wood pigeons, but not on my antennas! In residential
areas over here, generally people don't like to see lots of aluminum
in the air.

So for my situation it is not the less then 0.5 dB addditional gain
over a classic 4 radial GP, but just the common mode issue together
with visible apearance (I don't want 4 radials). Note that we have
maximum 400WPEP in PA-land, that also makes it easier.

In practicality, you will see little difference between 2, 3, or 4 radials.

You will have common mode currents of some magnitude with ANY GP type
antenna.

You will be hard pressed to notice 1 dB difference in a typical amateur
system.



--
Jim Pennino