Topband: Modeling "Ground" and losses

[Richard Fry]

Reply to W8JI post of Sat, 28 Feb 2015 19:14:07 -0500:

>>The source of the r-f current flowing on buried radials is the r-f current 
>>flowing in the earth as a result of radiation from the vertical monopole. 
>>(etc)

>It seems to me that answer ignores other effects.

>1.) If we remove the earth, the radials still have current.

Yes, but then the origin of that current is via a direct, metallic path back 
to the 2nd terminal of the source (transmitter), using either balanced or 
coaxial transmission line.

That operating configuration is different than when the radials are buried.

>2.) If we place a conductor almost anywhere near any antenna, connected or 
>not, it has current. If the wire is long and at 45 degrees or less, it can 
>have very high current.

But if those conductors are not buried, then the source of that current did 
not incur losses by traveling from the monopole to, and through the lossy 
earth around the base of the monopole -- to reach those radials.

>3.) With the same applied power, a single radial in earth, despite being in 
>the same dirt, has more current than the same radial with just one opposing 
>radial. It's collecting from the "same dirt".

A single buried radial may have more current as you suggest (I'd have to 
model this), but that might be expected because a relatively small amount of 
the earth current flowing near the location where an opposing radial might 
have been can then collected by the remaining radial.

No doubt the total current collected using both radials in this scenario is 
greater than when using either one of them, alone.

>4.) Groundplanes still have current in radials

See comment to 1.) above.
________________

Reply to KR9U post of Sat, 28 Feb 2015 21:23:50 -0500:

>... If I add an imperfect ground with the radial buried just below the 
>ground, I would expect that the efficiency of the antenna would drop.  NEC4 
>shows it loses about 10 dB vs. free space, with about 6 dB of directivity 
>in the direction of the radial wire using average ground.  If I use dry 
>sandy ground, then we gain back about 3 dB with a very similar pattern. ...

Wouldn't that tend to show that a monopole system using a very high-loss 
ground plane should have greater gain than when driven against a very 
low-loss ground plane?

Given that your NEC4 model is a 160-meter monopole system and other things 
equal, what does it show when only one 0.5-meter radial wire is used, and it 
is buried several centimeters below the surface of  0.1 mS/m d.c. 5 earth?

>If you are correct, then we should all be using uninsulated wires for 
>radials. ??

EM radiation/current passes through the insulation of buried radial wires as 
easily as it does through the insulation of aerial wires.

R. Fry