I don't really know for sure. But from modeling it and the article, I
suspect not. He only talks about lack of 50 kW capable low Z strapping down
to a radial field. He doesn't specifically say *no* ground screen. I
suspect there is something directly underneath each of the monopoles, but I
don't know that. There should be something in the magnitude of 700
volts/meter RMS field directly underneath and over 25 V/m inside a 50'
radius. Would think that would they would do something right underneath for
to keep from setting stuff on fire. One other antenna I know of that is a
low-end-of-the-BC-band vertical halfwave fed in the center (with the same
issue near the ground) has a heavy screened cage directly underneath.
The modeled field drops very rapidly from the maximum 700 V/m directly
underneath to 250 at 10 feet, 81 at 25 feet, to 28 at 50 feet to reach a
minimum of about 8 V/m out 100 feet then gradually back up to 15 V/m out
around 400 feet and then very gradually drops to 3.88 V/m at one mile. This
is remarkably close to the measured 3.55 quoted in the article. The 400
feet would be the maximum loss pattern intercept of the ground, and getting
beyond typical radial fields for 1/4 wave verticals at this frequency.
Since the model without any screening is slightly better than their
measured, the odds are no screening.
Don't want to get near the base of that thing running with anything metal on
you. Set yourself on fire.
73, Guy.
On Fri, Sep 23, 2011 at 6:45 PM, Milt -- N5IA <n5ia@zia-connection.com>wrote:
> Guy,
>
> Do I read the article correctly that there is little grounding and no
> radial screen under these monsters. Is that correct?
>
> Milt, N5IA
>
>
>
> -----Original Message----- From: Guy Olinger K2AV
> Sent: Friday, September 23, 2011 1:43 PM
> To: herbs@vitelcom.net
> Cc: topband@contesting.com
>
> Subject: Re: Topband: Effect of current max not at base of vertical.
>
> See
> http://www.fybush.com/sites/**2005/site-051028.html<http://www.fybush.com/sites/2005/site-051028.html>
>
> For 1530 kHz, that's a PAIR of two vertical halfwaves in phase. 50 kW
> gives 3545.89 mV/m. Note the relative lack of neighbors, and therefore lack
> of 24 hour miscellaneous diodic signal demodulation, talking window
> screens,
> permanently lit florescent bulbs, etc.
>
> Note that this monster is not too far from 160m. Think big and put an only
> slightly downsized 160 version out in the salt shallows somewhere on the
> western side of Cheasapeake Bay. Without any controversy whatsoever as to
> ground induction losses (zero) EZNEC says this would put 13.6 dbi gain
> toward Europe at 3.1 degree takeoff. Order of magnitude: three element
> yagi.
>
> Just for comparison, if I drain Chesapeake Bay and fill it with concrete
> rubble and other urban debris (can do magical things in EZNEC) I get 5.0
> dbi
> at 12.9 degrees. The full table:
>
> Urban debris: 5.0 @ 12.9d
> Sandy 4.8 @ 10.7d
> Rocky, poor 5.2 @ 10.6d
>
>
>
>
> On Fri, Sep 23, 2011 at 1:21 AM, Herb Schoenbohm <herbs@vitelcom.net>
> wrote:
>
> George, Are you familiar with the Franklyn antenna design?
>> Some broadcasters swear by them and claim a 3 db increase over a 1/4
>> vertical radiator.
>>
>> ______________________________**_________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
>
>
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