Steve Courtis - Starduster Install in Melbourne

[The DB]

Its not a matter of having enough radials or not, I doubt it is possible to have enough 1/4 wavelength radials to simulate a perfect ground in the first place.

Here I have a picture of the graphical layout of the model.

Here we have a single 1/4 wavelength vertical element directly attached to the perfect ground. There are no radials because the perfect ground is the radial system in this case.

Now the main screen view which includes the impedance of the antenna's feedpoint.

The impedance here shows an R = 35.9 when X = -0.02.

A few radials are simply not enough to simulate the perfect ground required to get the 35 to 36 ohm impedance...

When it comes to a 1/4 wavelength antenna with 4 radials, I get very close to the same impedance results as you do, and in that case, I agree that those are the results you should get.

You know its strange, I seem to remember you having a discussion with someone, Captain Kilowatt maybe, where he was able to get you to get very close to simulating a 36 ohm impedance for a 1/4 wavelength groundplane using some large number of radials... Maybe I'm mistaken...


The DB

 

[Captain Kilowatt]

A few radials are simply not enough to simulate the perfect ground required to get the 35 to 36 ohm impedance...

When it comes to a 1/4 wavelength antenna with 4 radials, I get very close to the same impedance results as you do, and in that case, I agree that those are the results you should get.

You know its strange, I seem to remember you having a discussion with someone, Captain Kilowatt maybe, where he was able to get you to get very close to simulating a 36 ohm impedance for a 1/4 wavelength groundplane using some large number of radials... Maybe I'm mistaken...


The DB

Try 120 radials and see what happens. I remember the discussion and I mentioned that we had seen VERY close to 35-36 ohms at an AM broadcast site with 120 radials of 10 gauge solid copper wire buried about six inches deep in prime dyke land which constituted very good agricultural soil. In the immediate area surrounding the tower base there was a ground mat made of 6 gauge wire. This was about 20 feet in diameter and consisted of several concentric rings and radials forming a heavy ground mat directly under the tower. All connections were made with Silfos-15.

http://www.silfos.com/products/catalog/Sil-Fos-15-Silvaloy-15-orderby0-p-1-c-62.html

 

[Marconi]

Thanks DB for showing us this distinction for how theory determines the 36 ohm feed point impedance for a 1/4 wave ground plane...using no radials, and a perfect ground plane instead.

After I got my first analyzer...I still don't recall ever seeing such a resistive match on my 1/4 wave whips. Thanks for showing us the source and results for this issue.

I'm not sure, but I think if such a discussion with CK happened, it was probably concerning broadcast radio's ground mounted verticals in the early days of Public Radio in America. Here the stories go...that the best antenna gains for such tall antennas were at or near 1 dbi...and every little advantage possible was eked-out trying to improve that gain, so they added many radials, among other design ideas.

 

[steviethefireball]

Lovely machined mount, nice install and then he goes f'ks it up by using one of those stupid 6 spoke "ground plane for CB radio" things that doesn't even fit on the ground side of the antenna.

The six spoke radials gave the antenna more bandwidth.

 

[1KT001]

Questa è l'Italia Starduster

STARDUSTER M-400

1/4 λ ground plane, Omnidirezionale, 26.5 ... 30 MHz Tarabile, Sistemi: 10m-HAM

www.sirioantenne.it