I have an elevated vertical (GP) on 160. . . it's hung off of the 120'
guy ring of a 130' rotating tower. . . it has about a 35 degree slope to
it. It's fed 10' off the ground and has 3 elevated radials about 10'
off the ground. It's sure not a dummy load. . . from Iowa, I've worked
87 countries on it since I put it up Oct 26.
73. . . Dave
W0FLS
> ----------
> From:
> 10eesfams2mi@mail20.MCIONE.com%INTERNET[SMTP:10eesfams2mi#064#mail20.M
> CIONE.com%INTERNET@email.mot.com]
> Reply To: w8ji.tom@MCIONE.com%INTERNET
> Sent: Thursday, March 05, 1998 12:19 PM
> To: TOPBAND@contesting.com%INTERNET;
> TOWERTALK@contesting.com%INTERNET; DX@VE7TCP.AMPR.ORG%INTERNET;
> n4kg@juno.com%INTERNET
> Subject: Re: TopBand: Elevated GP vs. Vertical Antennas
>
To: <towertalk@contesting.com>
> > Date: Thu, 05 Mar 1998 08:15:23 -0600
> > From: n4kg@juno.com (T A RUSSELL)
>
> Hi Tom,
>
> Gee, this sure spread to lot's of groups!
>
> While that is a novel and simple feed method, and very creative,
> users should be aware of some potential problems (just like many
> antennas--such as slopers or zepps--have).
>
> > I agree that my elevated GP antennas have losses due to the earth
> > connection
> > and low radials, but you make it sound like such antennas are not
> much
> > better than a dummy load and on this point I must STRONGLY
> DISAGREE.
>
> That's true. Even if efficiency is less than 10% it is still much
> better than a dummy load, and the antenna will certainly produce many
> DX contacts. People even work DX with Gaps on 160, and some Hams are
> quite happy with even grossly inefficient antennas.
>
> > (My GUESS at WORST CASE losses compared to a full size ground
> based
> > vertical with lots of radials is 6 dB. My HUNCH is that it is
> actually
> > much LESS.)
>
> On the other hand WR4U picked up about 10 dB (groundwave
> measurement) when he changed over from the system discussed to a
> conventional shunt fed system with only about a dozen ground mounted
> radials.
>
> The main problems in establishing performance are unpredictable
> values of earth-to-tower-base resistance at the bottom, as well as
> not knowing exactly what's above the radial-to-tower feedpoint
> connection or below and around the radials.
>
> All of this has an awful lot to do with the efficiency of the overall
> system.
>
> There are three known but unpredictable losses at work.
>
> One is earth loss because of the poor radial system. Measurements
> show that loss is typically six dB or so with a full size radiator
> (and MORE in a close spaced phased array or with a short radiator)
> when using a small close to ground elevated system, when compared to
> a conventional system. Adding more radials helps this problem by
> reducing current flowing through the lossy soil.
>
> The second is coupling from the radials to anything and everything
> else around the radials. This is caused by the high induction
> (electric and magnetic) fields around the radials. Contrary to rumor
> this source of loss only greatly diminishes in the far field, and is
> helped very little (if at all) by "balancing the current" in the
> radials. Adding more and longer radials DOES help this problem,
> however by reducing the field intensity around each radial.
>
> The third source of loss is the end of the radiator is stuck down in
> the mud, and excited by the feedpoint just as the rest of the tower
> is.
>
> To see interesting and more accurate modeling results, model the
> antenna "correctly" by inserting a resistive load between the bottom
> of the tower and mininec based ground. This resistance partially
> corrects for mininec's incorrect assumption that anything connected
> to the ground is a perfect zero ohm lossless connection.
>
> There have been a lot of incorrect ideas presented that resonant and
> properly tuned radials don't radiate in the near field. My post was
> not intended so much to impugn your feed system as to simply point
> out the user should be aware that his results may not be anywhere
> like other people experience, because elevated radials (and even a
> hot tower stuck in the mud) make for a very unpredictable system.
>
> Predicting or even discussing the results of running a Beverage or
> any other conductor near such a tangled unpredictable mess of
> conducted and radiated fields is a waste of time and bandwidth. It's
> all blind luck.
>
> I hope this clarifies my point.
> 73, Tom W8JI
> w8ji.tom@MCIONE.com
>
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