Topband: Ground mounted 1/2 wave

[Carl]

I guess I wasnt clear enough so lets start again.

We both agree that the .38 db increase is at all elevation angles since the 
increase in efficiency at the feed doesnt change the pattern shape, just 
levels. OK ?

Where the differences are is in the initial far field signal strengths from 
zero to lets say 20 degrees. With a perfect theoretical ground the levels 
are the same. If that held in reality then no matter what the ground losses 
are the BC stations would not be spending the big bucks in radial fields, 
even for 1/2 waves.

The city lot ham would be readily competitive with the antenna farm operator 
or the little guy in a coastal salt water swamp.

My point all along is that ground losses change the shape of the main lobe 
curve at low elevations and reduce signal levels there. Total power doesnt 
change but it is no longer all radiated, some is now dissipated in the lossy 
ground. Basic physics tell us you cant have both at the same time.
BC stations arent allowed to do that since it is the ground wave they are 
required to radiate to their local audience, the sole reason of their 
existence except for the few clear channel flamethrowers. A good ground wave 
signal means a good amount of power in all of that main lobe which results 
in the nightime skywave BCB DXers crave. Hams want some of that low angle 
just above the ground wave to work DX and those that radiate a high 
percentage of the output fed into the antenna to cover all those angles win 
the gold. Other than saltwater there is no magic fix as some want you to 
believe.

Many years ago there was a BC station in Lowell, MA that had a tower on a 
4th story industrial building metal roof, that was the total ground. Im 
about 6 miles LOS from there and the selective fading was intense. Their 
ground wave was minimal but somewhere along the way the FCC allowed them to 
operate. I dont remember the details but there were several "stories" 
floating around about why they kept operating. It all went away during the 
urban renewal of Lowell, establishment of an Urban National Park, and a huge 
city investment in its future.

I suppose hams can use a high end local BCB station to evaluate changes as 
they make them. Find a moderately strong steady station and monitor/chart 
its strength for several days of the same weather. Then by adding radials, 
rods, screens, perimeter wires, etc progress (or lack of) can be tracked.
By doubling radials each time from 4 to 32 or even 64 and having them all 
precut and ready to unroll this can be done in a few hours especially with a 
helper. Next comes the screen.

Carl
KM1H

----- Original Message ----- 
From: DAVID CUTHBERT
To: Carl
Cc: Tom W8JI ; Donald Chester ; topband at contesting.com
Sent: Tuesday, December 18, 2012 8:00 AM
Subject: Re: Topband: Ground mounted 1/2 wave





On Mon, Dec 17, 2012 at 8:41 PM, Carl <km1h at jeremy.mv.com> wrote:


Subject: Re: Topband: Ground mounted 1/2 wave


**  All that means is that the elevation peak of the wave as seen in the 
typical 2D plot increases by .38dB and as expected. It does not say what 
happens from that peak down to zero elevation which is what 160M DXers care 
about.

What is the FS at 5, 10 degrees when going from a ground rod to a full bore 
radial field over a wide range of ground conductivity?


Carl
KM1H

Yes, it does say what happens from that peak down to zero elevation. It says 
that the signal increases by 0.38 dB.

To test this I ran two EZNEC simulations. One is a 90 degree vertical over 
thirty 90 degree radials over medium ground. The antenna is driven with 1 kW 
and the E-field at one mile is recorded from a height of 10' to 1000'. A 
second 90 degree vertical over four 23 degree radials driven with 1 kW and 
the E-field at one mile is recorded from a heights of 10' to 1000'. The 
difference in E-field AT ALL ELEVATIONS is 0.86 dB.

   Dave WX7G




_______________________________________________
It is undesirable to believe a proposition when there is no ground 
whatsoever for supposing it is true. — Bertrand Russell





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