Ground conditions wet vs dry farmland

[RadioDaze]

Hi there I am wondering what good ground is typically and if that changes after heavy rainfall.

As I gather ground affects antennas significantly. I understand it can causes losses and reflections. Losses are... well... negative we can assume as it is the ground absorbing valuable RF energy away from places where it can be better used (or is that just deconstructive phase cancellation from a ground reflection ?) and reflections can be constructive or destructive in phase.

I read something that desert is the worst possible ground and that a salty bog is very good ground.

I am interested to understand more about how the ground effects radio waves from an antenna. I currently exclusively use verticals antennas and as I understand in general terms the ground is best avoided by mounting your antenna 1 wavelength high and above within reason if possible.

That somewhat suggests the ground has a negative influence on the antenna and seems to be lossy.

Is dry farmland after a summer more lossy than wet farmland ?

 

[RadioDaze]

Does anyone know anything about ground conditions? Thanks.

 

[The DB]

Farmland in general is one of the better ground types. For any given ground type, wet is always better than dry.


The DB

 

[RadioDaze]

Thanks The DB. I did go looking myself and found this.

http://www.iw5edi.com/ham-radio/?perfect-ground-vs.-poor-ground.-what-is-the-difference-,143

The guy seems to think there is not immense differences between the ground conditions in the 10-12M bands.

When people speak of ground losses does that mean the signal is literally absorbed by the ground under the antenna instead of being radiated in a useful manner. Or that there is destructive reflection causing a second wave that is a little out of phase causing a signal loss on the horizon.

 

[The DB]

Lower frequencies do tend to penetrate things like the earth much deeper than higher frequencies. I don't know, however, how much of a difference that, say, 30 MHz will have compared to 1 MHz. That is the first such chart I've seen, and I will have to do more such research.

From my modeling experience, I do know that even at 30 MHz that there are differences in a vertical antennas radiation patterns, and I would agree that in most cases, you won't notice that difference in gain by using a radio's s-meter. In some cases, surprisingly, the antenna modeled over "poor" ground actually performed better than antenna modeled over "average" and "good" grounds...

I will have to check out the single source listed on your linked page. Hopefully I can find it as the reference listed on said page is not very descriptive...

Yes, ground losses are from signals being absorbed by an imperfect ground. As lower frequencies tend to penetrate deeper into the earth, they will naturally have more in the way of losses, at least when referring to the frequencies that ham radio operators have access to. Further, mounting an antenna higher above an earth also has the effect of lessening ground losses, at least to a point.


The DB

 

[Road Squawker]

...http://www.iw5edi.com/ham-radio/?perfect-ground-vs.-poor-ground.-what-is-the-difference-,143

The guy seems to think there is not immense differences between the ground conditions in the 10-12M bands....

he seems to contradict himself,....actually he mixes radiation angle and ground loss, and then talks "apples and oranges"......first he says: " The influence of ground conductivity becomes less important at 14MHz and higher (1.2 dB difference or less)."

then he says:"However, in most "real world" cases, the 30m/90ft height is less advantageous than you might think.

Why is this the case?

The angle of radiation can be so low that most of the signal is eaten up by ground loss. For the 21MHz, 24MHz and 28MHz bands, an antenna on a 30m/98ft high tower has a radiation pattern of 5 degrees or less (depending on ground conditions, the electrical height may be even higher and the angle of radiation even lower). At these low radiation angles, the ground tends to absorb a large portion of the signal.


bottom line: get the antenna as high as you can, and turn on da sprinklers

 

[wavrider]

On verticals the ground loss doe snot play much of a factor IF the vert is installed at a decent height above ground.

Decent is dependent on wavelength of the vert.

Horizontal antennas is where the ground loss really comes into play based on the 6db of ground gain that is added to a horizontal antenna.

The more loss in the ground the less gain added to a horizontal antenna.

Sp get that vert up as high as you can within reason, start making contacts and to hell with the ground loss, you basically have no control over the type of ground you are on.

For sprinklers, if you are really wanting to wet the ground do it about 8 wave lengths from the base of the antenna

 

[Captain Kilowatt]

We could notice a definite difference in signal levels at the edges of our service contours of our AM broadcast stations depending on the time of year. In spring when the ground was saturated the signals were noticeably stronger than in the late summer. The higher the frequency the lesser the effect.

 

[RadioDaze]

Great replies thanks people !