On Fri, 6 Mar 1998 09:00:43 -0600 Dave Raymond-CSUS04
<Dave_Raymond-CSUS04@email.mot.com> writes:
>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
Sounds good Dave.
My wire verticals are full size also and hung from the top guys of a 180'
tower. They are about 50-60' apart total at the top and 130' apart at
20' above ground with 12 or less elevated radials (the less is based upon
what breaks since they are only #16 ). The feed is a basic ON4UN 78
degree hunk of coax switched into 2 noise bridge measured 1/4 wave lines.
I can also feed both in parallel so I wind up with NE or SW cardioid or
NW/SE broadside. Real basic, simple and no funny parts to fail...just 2
cheap DPDT relays and some 75 Ohm freebie drop cable RG-11 for feeds.
Main feed line is 250' of 3/4' CATV hardline...also free.
Pattern varies depending on gnd and band condx but 15-20 dB F/B is
typical.
With a LK500ZC at 1200W and 264 countries I cant complain.
Hearing the DX is usually the primary factor.
73 Carl KM1H
>
>> ----------
>> 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: <topband@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
>>
>> --
>> FAQ on WWW: http://www.contesting.com/topband.html
>> Submissions: topband@contesting.com
>> Administrative requests: topband-REQUEST@contesting.com
>> Problems: owner-topband@contesting.com
>>
>
>--
>FAQ on WWW: http://www.contesting.com/topband.html
>Submissions: topband@contesting.com
>Administrative requests: topband-REQUEST@contesting.com
>Problems: owner-topband@contesting.com
>
_____________________________________________________________________
You don't need to buy Internet access to use free Internet e-mail.
Get completely free e-mail from Juno at http://www.juno.com
Or call Juno at (800) 654-JUNO [654-5866]
--
FAQ on WWW: http://www.contesting.com/topband.html
Submissions: topband@contesting.com
Administrative requests: topband-REQUEST@contesting.com
Problems: owner-topband@contesting.com
|