Topband: Ground mounted 1/2 wave

DAVID CUTHBERT telegrapher9 at gmail.com
Tue Dec 18 12:07:00 EST 2012


Where is the helicopter you insisted we need?
On Dec 18, 2012 10:03 AM, "Carl" <km1h at jeremy.mv.com> wrote:

> 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
>
>
>
>
>
> No virus found in this message.
> Checked by AVG - www.avg.com
> Version: 10.0.1430 / Virus Database: 2637/5468 - Release Date: 12/18/12
>


More information about the Topband mailing list