Radials on .64 wave vertical - Straight or angled?

[HomerBB]

These were done for me by Marconi. We were having a one-on-one discussion about the length and angle of radials. We didn't discuss the lack of them at the time.

 

[M0GVZ]

Yup.
But the poster was referring to CB antennas not ham gear.
You don't talk/listen with the CB any more; do you?

Its not ham gear. An antenna doesn't give a stuff what its connected to. Antennas aren't CB or HAM specific.

 

[The DB]

I thought I remembered more to the .pdf HomerBB was kind enough to link for us so I did some playing with 4nec2...

For reference the bottom of the 5/8 wavelength vertical element is 1 wavelength above average ground. Radials in most models drop below this point as they are angled down. Also the asteric (*) is used in place of a degrees symbol.

First up, the reference 5/8 antenna with four radials at 90*.

Impedance: 71.5 - j259
SWR: 20.9

This looks like a standard 5/8 wavelength antenna pattern to me.

Next up, 5/8 antenna with four radials at 75*.

Impedance: 68.6 - j248
SWR: 20

Comparing the two you will note that impedance, SWR and reactance have all dropped some. Gain has also gone up, but not where we want it to have gone up. The low angle lobe gain is virtually unaffected while the 45 to 50 degree high angle lobe has surpassed the low angle lobe as the dominant lobe.

I've modeled every 15* radial angle down to 0* (or in line with the upper 5/8 vertical section), and the impedance and SWR seems to drop down to 15*, then both jump up at the 0* point. The lowest SWR present is 10.8 at the feedpoint. The desirable low angle lobe drops off and the high angle lobe gets to be more dominant as you lower the radial angle... I have the models and data saved if anyone really wants to see it all...


The DB

 

[W5LZ]

So it appears that there's no particular benefit to the number of radials, their length or their 'angle'. Sure, there are differences, but just how significant are they?
- 'Doc

 

[The DB]

So it appears that there's no particular benefit to the number of radials, their length or their 'angle'. Sure, there are differences, but just how significant are they?
- 'Doc

Here is a plot with the radials at 45* off of vertical...

And further down at 15* off of vertical...

The low angle lobe drops off from the maximum gain (3.17 DBi) with the standard radials at 90* off of vertical to about 0 DBi with the radials at 15* off of vertical. That is a pretty big drop of the low angle lobe, but the drop is mostly consistent as you angle the radials down.

When it comes to radial length, I'll play with that later when I get the chance...


The DB

 

[W5LZ]

... and will still make little to no significant difference in how the thing performs.
- 'Doc

 

[SuperNasty]

Thanks The DB for putting the charts up and the work, interesting stuff. I have the radials now on the Imax 2000, around 8ft horizontally mounted at the bottom U bolt (as Solarcon suggests for their GPK kit), I cant actually angle the radials as each radial is one piece made from sections of a Maco V Quad. The antenna is up about 34ft or so and is not insulated from the mast, I don't use a coax choke. If I do decide to use a choke I might electrically isolate the antenna and radials from the mast and see what happens.

The SWR reading is below 1:5 from 25.2 MHz to 28.2 MHz, there is a slight increase in SWR specifically at 26.9 MHz where it rises from near 1:1 to 1:4 then back down to near 1:1 again, I had not noticed this before without radials and don't know why that is. Not that it matters but interesting never the less.

Anyway I cant say that it's not working, ground wave signals are up a few notches from the CTE Top One I had up previously and DX is still rolling in (as it did anyway). Still a level of noise here (about 3 to 4 on the S meter).