Radial length and angle radiation patterns... Long...

[The DB]

DB, GHZ24 is right, but try adjusting the segment numbers and tubing diameters closer to the same values and maybe you can fix the angle error problem without building a hub to connect the radials to the radiator.

Check your Average Gain results too.

What are the dimensions and segments for the radiator and radials for this 5/8 wave? I could fix my model and maybe it will be closer to your results.

They are all using .01 mm diameters. I was using .0001 mm diameters in the past, namely when refering to the Vector antennas as a way to get around the same angle problem mentioned in posts above.

I can get you exact dimensions if you like, however, they are in meters, not feet/inches.

Here is the .nec file for the 15* radial set without the central conductive mast.

GW	1	63	0	0	11	0	0	17.875	.01	'.
GW	2	25	1.7795	0	4.3593	0	0	11	.01
GW	3	25	-1.7795	0	4.3593	0	0	11	.01
GW	4	25	0	1.7795	4.3593	0	0	11	.01
GW	5	25	0	-1.7795	4.3593	0	0	11	.01
GE	1
GN	2	0	0	0	13	0.005
EK
EX	0	1	1	0	1	0	0	'Voltage source (1+j0) at wire 1 segment 1
FR	0	0	0	0	27.185	0
EN

And here is the single 0* radial set...

CM 
CE
GW	1	63	0	0	11	0	0	17.875	.01	'.
GW	2	63	0	0	4.125	0	0	11	.01
GE	-1
GN	2	0	0	0	13	0.005
EK
EX	0	1	1	0	1	0	0	'Voltage source (1+j0) at wire 1 segment 1
FR	0	0	0	0	27.185	0
EN

You will find fairly high segment counts. I tend to use 100 per wavelength and then divide, so 25 for a 1/4 wavelength section, 63 for a 5/8 wavelength section, ect.


The DB

 

[The DB]

I have done some modeling of 1/4 wavelength horizontal radials, single 5/8 wavelength vertical radial, and 4 5/8 wavelength radials at 15* off of vertical. I modeled them at 2, 3, and 4 wavelengths above the average ground used before.

The model with the 1/4 wavelength horizontal radials gain data:
1 wavelength : 3.17 dBi
2 wavelengths: 4.59 dBi
3 wavelengths: 4.61 dBi
4 wavelengths: 3.18 dBi

The model with a single vertical 5/8 wavelength radial:
1 wavelength : 4.77 dBi
2 wavelengths: 7.22 dBi
3 wavelengths: 8.24 dBi
4 wavelengths: 6.87 dBi

The model with four 5/8 wavelength radials 15* off of vertical:
1 wavelength : 6.01 dBi
2 wavelengths: 7.77 dBi
3 wavelengths: 8.82 dBi
4 wavelengths: 7.60 dBi

NOTE: I have the pictures available, and will post them when my web sites DNS issues are resolved...

As I raised the antenna higher the gain figures of a single lower 5/8 wavelength radial model very quickly achieved significant gain over the standard 1/4 wavelength horizontal radial models. At three and four wavelengths above ground the gain difference is beyond 3 dB. While there was gain either way there was simply a lot less of it near the ground, so this antenna design is definitely ground sensitive...

Additionally, at the three and four wavelength heights the 1/4 wavelength model have several secondary lobes that are within 2 dB of the peak lobe. On the 5/8 wavelength vertical radial models at three and four wavelengths high there is in excess of 6 dB difference from the main low angle lobe to the other lobes, in one model this difference is pushed to about 8 dB of difference.

Again, I'll have the plots that show this data when my web site is fixed...


The DB

 

[The DB]

Here are the plots I said I had earlier. They are in groups of three, the first one in each set is the 1/4 wavelength horizontal radial model for comparison. The second is the single 5/8 wavelength vertical lower radial, and the third is the four 5/8 wavelength lower radials at 15* from vertical.

First the one wavelength above earth set.

These are taken from above and included here for reference.

Next the two wavelength above earth set.

You will note the patterns, the middle plot (single 5/8 wavelength vertical) now looks and is radiating more like the antenna with four 5/8 wavelength radials that are 15* off of vertical...

The three wavelength above earth set...

In these you can clearly see that the low angle and vertical 5/8 wavelength radial antennas both have in excess of 3 dB gain over the antenna with 1/4 wavelength horizontal radials at the same height.

The four wavelength above earth set...

All antennas here have lost gain compared to when they were modeled three wavelengths above the earth, but the antenna with four 1/4 wavelength radials still lags the other two by at least 3 dB in gain.

Conclusion at this point, the low angle 5/8 wavelength radial version of the antenna and the antenna with a single vertical radial do have low angle gain over a standard 5/8 wavelength antenna with 1/4 wavelength radials, at least in most situations (I have yet to see a model or plot that shows otherwise). If you get the height of the antenna right the gain is in excess of 3 dB, or effectively double the power at its peak low angle gain.


The DB

 

[Robb]

Perhaps you can model a 5/8 lw isolated mast 1 wl above ground with a coax choke at the 5/8 wl from the feedpoint?

 

[wa1knx]

choked mast

I was looking for an 5/8 design I tripped over a while back that had 1/4 radials
going upward around 45, (but not like the vector). I instead found
an article "double 5/8 flower pot antenna" by vk2zoi. for 2mtrs, its choked off
at the base and the author measured 3db+ over a 1/2 wave. he uses stubs
in this design to broadband the antenna.

 

[W5LZ]

I think 'VK2ZOI' has an interesting approach to antennas. I also think he explained about the so called 'gain' of his antenna project(s), nothing definite by any means.
If you take a look at his 'pot' antennas, they have a marked resemblance to a bazooka and Zepp! Absolutely no reason why either/both wouldn't work just dandy at VHF if scaled properly.
- 'Doc

 

[wa1knx]

scaled antenna

doc, he sure does have interesting antennas. I bet they would scale to 11mtrs.
A pair of 5/8s would be like a 45' long antenna, but choking at the mast
could work. ie using it as a mast and antenna. dean

 

[wa1knx]

5/8 with inverted radials

This is a ham (9w2xan) that has a 5/8 with inverted radials. I have a note out to him with questions..

9W2XAN: Bengkel Antenna 5/8 @ Astra @ Kaki Biawak

scroll down to his bengkel antenna.

I'm not sure of the dimensions, but it would be interesting to see a
model with 1/4 radials angling up 45 degrees DB (or anyone). He has
an interesting site as well.

 

[The DB]

This is a ham (9w2xan) that has a 5/8 with inverted radials. I have a note out to him with questions..

9W2XAN: Bengkel Antenna 5/8 @ Astra @ Kaki Biawak

scroll down to his bengkel antenna.

I'm not sure of the dimensions, but it would be interesting to see a
model with 1/4 radials angling up 45 degrees DB (or anyone). He has
an interesting site as well.

Sure...

This is exactly the same as my models above in the first post of the thread, only the 1/4 wavelength radials are pointed up 45 degrees.

For comparison here is the model with 1/4 wavelength horizontal radials...

There is a 0.25 dB difference in gain between them, you won't notice that difference.


The DB

 

[HomerBB]

This Bengal antenna is a dipole, center fed, with the coax traveling up through the lower tube. It has radials, but it does not appear to be an end fed 5/8 vertical with upward pointing radials at all.

You'll note that the builder points out that the upper and lower tubes are separated by a center insulator, and are each of them made of 1/2" alloy (sic- aloy) or aluminum tube, and are fed at the center point with the coax center and braid to each tube. I have made several of these and recognized the construction immediately. I have not made the radials on them as shown.

 

[HomerBB]

Kayu Penyapu 5 inci
Di Tebuk Lubang
3/4 inci Pernisah Antenna 2 Tiang Aloy

translation:

Wood Sweeper 5 inches
In the perforation hole
3/4 inch splitters Mast Antenna 2 Aloy

 

[The DB]

Ahh, ok, so the feedpoint isn't at the base... Corrected that.

The DB

 

[wa1knx]

upward radials

thanks DB. in the first two models (45up, 90horz) I see the higher angles pushed around a bit,
some down and others up. I did find this looking at 5/8 antennas. but only one
other site some time back, have I seen the upward radials. I havn't heard back from builder so I am still curious as to any advantage of doing this.